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ICAM 2011 poster Abstracts


Session Number: P1a
Presenting Author: Ian Renfrew
Author Email: i.renfrew@uea.ac.uk
Author Affiliation: School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
Co-Author: Stephen Outten, Nina Petersen
Co-Author Affiliation: UEA
Abstract Title:
An easterly tip jet off Cape Farewell, Greenland
Abstract:
The coastal seas around Greenland are the windiest in the world ocean. Greenland is located close to the primary North Atlantic stormtrack, and the impact of Greenland’s high and steep topography on the passing synoptic-scale storms results in a plethora of low-level jets around the coast. Off the southernmost point, Cape Farewell, low-level “tip jets” are common in both westerly and easterly directions.
An easterly tip jet event off Cape Farewell, Greenland, will be described and analysed through both aircraft-based observations and numerical simulations from the Greenland Flow Distortion experiment. In situ observations reveal a jet core at the coast with peak winds of almost 50 m/s, about 600-800 m above the sea surface, and of 30 m/s at 10 m. The jet accelerated and curved anticyclonically as it reached Cape Farewell and the end of the barrier. The very high wind speeds generated a highly turbulent atmospheric boundary layer and resulted in some of the highest surface wind stresses ever observed over the ocean.
The simulations make use of a limited-area 12-km-resolution configuration of the Met Office’s Unified Model. A momentum budget analysis along a curved locus through the core of the jet has been derived. Off southeast Greenland, the easterly tip jet was in cross-jet geostrophic balance, but was being accelerated downstream by an along-jet pressure gradient. Over the curved part of the locus, as the jet rounded Cape Farewell, a cross-jet turbulent flux-divergence suggests that the jet was unbalanced at the height of the jet core. This flux-divergence decreases in magnitude with height so that an approximate gradient wind balance applies in the upper part of the jet. The anticyclonic curvature, characteristic of easterly tip jets, was caused by a dramatic decrease in the cross-jet pressure-gradient force at the end of the barrier, after which the jet aligned with the synoptic-scale isobars and returned to approximate geostrophic balance.

Session Number: P1b
Presenting Author: Haraldur Ólafsson
Author Email: haraldur68@gmail.com
Author Affiliation: University of Iceland, Icelandic Meteorological Office and Institute for Meteorological Research
Co-Author: Hálfdán Ágústsson & Ólafur Rögnvaldsson
Co-Author Affiliation: University of Iceland, Icelandic Meteorological Office and Institute for Meteorological Research
Abstract Title:
Elements of orographic flow disturbances that dominate the long-term mean flows over Iceland
Abstract:
The wind climate of Iceland has been reconstructed by downscaling the ECMWF analysis on a grid of 3 km horizontal resolution. The persistence of gravity waves over the ice caps is clear in the simulations. There is also a more clear sheltering effect near coastal mountains in the summer, than in the winter. This can be attributed to a low Nh/U in the summer. There are however exceptions to the above summer sheltering, and these exceptions can be attributed to the sea breeze being accelerated in the vicinity of mountains.

Session Number: P1c
Presenting Author: Hálfdán Ágústsson
Author Email: halfdana@hi.is
Author Affiliation: University of Iceland, Icelandic Meteorological Office and Institute for Meteorological Research
Abstract Title:
Lee-side vortices over Reykjavík
Abstract:
Satellite images, an atmospheric sounding, surface based observations of weather as well as high-resolution simulations of weather are used to explore the asymmetric shedding of lee-side vortices from Mt. Snæfellsjökull on the Snæfellsnes peninsula in West-Iceland. The vortices were advected with the ambient flow to the southeast across the Faxaflói bay and over Reykjavík 3-4 hours after their generation. Further downstream and inland, the vortices were presumably disrupted and dissipated in the convective boundary layer. The observed winds aloft were approx. 8 m/s from the northwest in a well mixed boundary layer, capped by a sharp inversion at 900 hPa, well below the top of Mt. Snæfellsjökull. A thin layer of stratus clouds topped the boundary layer, above which the air was dry and stably stratified. The satellite images show the the generation and advection of the vortices while automatic observations of wind and solar radiation in Reykjavík document the passage of a vortex aloft and its progression inland. At the surface, the passing of the vortex is associated with a short and local clearing in the cloud cover as well as transient changes in the wind speed and direction. The mesoscale model reproduces the shedding of the vortices and their passage towards Reykjavík while some of the details are however incorrect.

Session Number: P1d
Presenting Author: Wolfgang Langhans
Author Email: wolfgang.langhans@env.ethz.ch
Author Affiliation: Institute for Atmospheric and Climate Science, ETH Zurich
Co-Author: Jürg Schmidli, Christoph Schär
Co-Author Affiliation: Institute for Atmospheric and Climate Science, ETH Zurich
Abstract Title:
Bulk convergence of kilometer-scale simulations of moist convection over complex terrain
Abstract:
The explicit treatment of deep convection at kilometer-scale resolutions has lead to improved quantitative precipitation forecasts over the last years. Still, simulations at “convection-permitting” resolutions are insufficient to fully resolve the complete spectrum of energy-containing motions of convection and thus rely on parameterizations to account for the sub-grid part of this spectrum. The benefits from a refinement of the resolution are unclear, since the convergence behavior of real-case simulations at kilometer-scales has not yet been studied in detail.
In this paper we are interested in bulk flow properties such as the Alpine-scale heat and moisture exchange between the PBL and the free troposphere during a nine-day summer period characterized by pronounced thermally-driven Alpine circulations and deep convection. To this end, real-case simulations are conducted over a large Alpine region using the COSMO-CLM model at grid-spacings of 4.4, 2.2, 1.1, and 0.55 km. To achieve consistency of the governing equations across the different scales, we begin our considerations with a set of simulations having constant turbulent length scales and use a grid-independent resolution of the underlying topography. Results are then compared against further sets, which differ only in their parameterization of turbulent processes (e.g. 1D vs. 3D LES formulation). Those additional sets allow for higher Reynolds number flows at higher resolutions.
We find that heat and moisture budgets of a large Alpine control volume (top at 4 km) are convergent at order one, while deep-convective heat and vapor fluxes are convergent at order two. These findings are similar to convergence properties found for the same numerical schemes, but from idealized simulations of 2D dry and linear flow over a bell-shaped hill.
Our results show that the effects of smaller viscosities at higher numerical resolutions enhance the convective overturning within the PBL. However, the impact of resolution on net advection of heat and moisture within the large control volume remains small, since vertical and horizontal advection partly compensate each other. Still, both the vertical exchange between PBL and free troposphere and deep-convective vertical fluxes of heat and vapor are sensitive to both resolution and the applied turbulence model. The relative difference between simulations using dx=1.1 and 0.55 km grid-spacings, respectively, is found to be smaller than 10 % for a 1D TKE-based scheme combined with a 2D Smagorinsky scheme for lateral diffusion.

Session Number: P1e
Presenting Author: Marius Opsanger Jonassen
Author Email: Marius.Jonassen@gfi.uib.no
Author Affiliation: Geophysical Institute, University of Bergen Allegaten 70 5007 Bergen
Co-Author: Hálfdán Ágústsson, Haraldur Ólafsson and Joachim Reuder
Co-Author Affiliation:
Abstract Title:
Persistency of mountain waves over glaciers in Iceland
Abstract:
Downscaling of the wind climate over Iceland along with observations from the FLOHOF field campaign, indicate a persistent downstream shift in the wind speed maximum over the main glaciers in Iceland. This suggests that gravity waves are an integral part of the surface wind climate in Iceland, the probable cause being the reduced friction associated with Iceland’s glaciated and sparsely vegetated mountains. A series of numerical sensitivity tests with the WRF atmospheric model suggest indeed that surface friction plays an imperative role in determining the presence of the downstream wind maximum and thus the gravity waves.

Session Number: P1f
Presenting Author: Guðrún Nína Petersen
Author Email: gnp@vedur.is
Author Affiliation: Icelandic Meteorological Office
Co-Author: Haraldur Ólafsson
Co-Author Affiliation:
Abstract Title:
More on the warming of the föhn
Abstract:
Numerical simulations and observations from Iceland are explored to shed a light on the heat source of the föhn. The data do not indicate a connection between the amount of precipitation on the upstream side and the downlope heating. However, a numerical simulation of a typical föhn case shows that precipitation may play a role in the downstream heating, but not through heating of the airmass, but by cooling of the low level flow, leading to enhanced blocking effect and stronger downdrafts on the lee side.

Session Number: P1g
Presenting Author: Željko Večenaj
Author Email: zvecenaj@gfz.hr
Author Affiliation: Faculty of Science, Department of Geophysics, University of Zagreb, Zagreb Horvatovac 95, Croatia
Co-Author: Danijel Belušić, Branko Grisogono
Co-Author Affiliation: Unive. of Zagreb, Faculty of Science, Department of Geophysics, Zagreb Horvatovac 95, Croatia
Abstract Title:
A case study of severe bora event at Vratnik Pass and Senj, NE Adriatic coast
Abstract:
Bora is a downslope windstorm that blows at the eastern Adriatic coast from the northeast quadrant, most often during winter seasons. It possesses a wide spectrum of average wind speeds, and due to its gustiness the speed maxima may surpass 60 m/s. During a bora event, the turbulence is strongly developed in the lee of the mountain.
Horizontal and vertical wind is measured at Vratnik Pass (44.98°N, 14.98°E, 600 m above MSL) at a height of 10 m above the ground, and down the slope, in the town of Senj (44.99°N, 14.90°E, 2 m above MSL) at a height of 13 m above the ground with the WindMaster ultrasonic anemometer (Gill Instruments). The anemometers simultaneously record the data in the period between October 2004 and September 2005 with a sampling frequency of 4 Hz. A case study is presented when bora occurred both at Vratnik Pass and Senj, former being the upwind elevated site for the later and well-known bora place. We address onset, evolution and cessation of bora at these two closely related places.
Besides a dynamical background, certain turbulence features of this bora event are assessed as well. Intriguing bora-flow related subtleties between the two representative sites are revealed. Regarding the both sites, different sub-regimes are indicated.

Session Number: P1h
Presenting Author: Kristian Horvath
Author Email: kristian.horvath@cirus.dhz.hr
Author Affiliation: Meteorological and Hydrological Service, Gric 3, 10000 Zagreb, Croatia
Co-Author: Zeljko Vecenaj, Branko Grisogono
Co-Author Affiliation: University of Zagreb, Faculty of Science, Department of Geophysics, Horvatovac 95, 10000 Zagreb, Croatia
Abstract Title:
Analysis of a strong mid-Adriatic bora event: the role of complex orography
Abstract:
While extreme bora winds in the northern Adriatic were since long in the focus of the relevant research, strong bora winds in the hinterland of Dalmatian coast are much less studied, yet frequent phenomenon in the region. The predictability of these events is considerably lower than for its northern counterpart due to the flow complexity induced by the chain of secondary orographic mountain sub-ranges and deep valleys.
A late winter case of a strong bora event in the mid-Adriatic was analyzed with the use of measurements and numerical experiments carried out with the WRF model. The analysis utilized three ultrasonic anemometers at 10 m, 22 m and 40 m levels and two additional classic cup and vane anemometers at 30 m and 60 m levels. The event was simulated with a number of numerical sensitivity experiments with modified orography.
The results assessing the observed and modeled properties of the selected bora event are presented. It is shown that the orographic complexity considerably modulates the bora flow. The observed and modeled turbulent properties, such as momentum fluxes and turbulent kinetic energy enabled the evaluation of the model performance as well as the assessment of the validity of similarity theory in the surface layer during the event. Certain differences in the bora subtle structure there and over the northern areas, the latter pertaining to more known bora cases, are pointed out.

Session Number: P1i
Presenting Author: P.W. Chan
Author Email: pwchan@hko.gov.hk
Author Affiliation: Hong Kong Observatory
Abstract Title:
A Significant Windshear Event Leading to Aircraft Diversion at the Hong Kong International Airport
Abstract:
A significant windshear event occurred in the early morning of 27 December 2009 at the Hong Kong International Airport (HKIA), leading to the diversion of three aircraft to the airport of Shenzhen (about 39 km to the north-northwest of HKIA). This paper documents the meteorological observations and predictions for the event. The significant windshear arose from disruption of the prevailing easterly to southeasterly flow by the complex terrain to the south of the airport. It was well captured by the Doppler Light Detection And Ranging (LIDAR) systems at HKIA, and as such the aircraft were given sufficient warning about the occurrence of significant windshear. The headwind changes along the glide paths as measured by the LIDAR were consistent with the aircraft measurements. The observations of the remote-sensing instruments during the event, including the LIDAR, are described in the paper. Moreover, this paper discusses the possibility of including windshear forecast information for flight planning purpose for this particular case. The forecast wind field near HKIA based on a high-resolution numerical weather prediction (NWP) model is described. For the present windshear event, it appears that the occurrence of terrain-disrupted airflow near HKIA may be forecast about 6 hours ahead. The timing of significant windshear is however not reproduced well in the NWP forecast.


Presentation Number: 19
Session Number: P1j
Presenting Author: Kayla Harrison
Author Email: kcharrison@alaska.edu
Author Affiliation: Arctic Region Supercomputing Center, University of Alaska Fairbanks, Fairbanks, Alaska, USA
Co-Author: Delia Arnold (2)(3), Irene Schicker (2), Don Morton (1)(4), Carl Dierking (5)
Co-Author Affiliation: (1) Arctic Region Supercomputing Center, University of Alaska Fairbanks, Fairbanks, Alaska USA (2) Institute of Meteorology, University of Natural Resources and Life Sciences, Vienna, Austria (3) Institute of Energy Technologies, Technical University of nces, Vienna, Austria (3) Institute of Energy Technologies, Technical University of Catalonia, Barcelona, Spain (4) Developmental Testbed Center (Visiting Scientist), National Center for Atmospheric Research, Boulder, Colorado, USA (5) Juneau Weather Forecast Office, National Oceanic and Atmospheric Administration / National Weather Service, Juneau, Alaska, USA
Abstract Title:
A high-resolution WRF simulation of a post-frontal topographically enhanced wind shear event at Juneau International Airport
Abstract:
Juneau International Airport in Alaska is surrounded by steep terrain, often presenting challenging conditions to departing aircraft. With the large majority of Instrument Flight Rules (IFR) departures occurring to the southeast, general aviation departure procedures for Runway 08 include a 180-degree right turn as soon as practical in order to avoid steeply rising terrain. Under strong wind conditions characterized by post-frontal topographically enhanced wind shear aircraft following these procedures may encounter turbulence or wind shear classified as severe. In January 1993 a Boeing 727 aircraft at a 30-degree bank encountered extreme crosswinds resulting in departure from controlled flight with successful recovery occurring within 50 meters of the ground. Carl Dierking (Dierking et al. 2011) has performed initial high-resolution WRF simulations of the January 1993 case as well as other events. In this work we focus on a similar post-frontal wind shear event at Juneau from December 2009. Dierking\'s simulation of this event is reviewed in the context of providing a basis for enhanced modeling with new initial and boundary conditions model parameterisations and higher resolution. The various modeling runs will be compared amongst themselves and with local observations - including those from the Juneau Airport Wind System (JAWS) - in order to determine which set-up (especially regarding horizontal resolution of the domains) performs better and would have potential to be used in the early warning systems of airports similarly located in complex terrain like the Juneau area.

Session Number: P1k
Presenting Author: Gunnar Livik
Author Email: gunnar.livik@student.uib.no
Author Affiliation: Geophysical Institute, University of Bergen Allegaten 70 5007 Bergen
Co-Author: Haraldur Ólafsson and Marius Opsanger Jonassen
Co-Author Affiliation:
Abstract Title:
Flow regimes and the quality of wind simulations in Spitzbergen
Abstract:
In the period 18 April - 1 May, 2010, automatic weather stations were placed at several location along Kongsfjorden, Spitsbergen. The atmospheric flow during the period is simulated with the Weather Research and Forecasting (WRF) mesoscale model with a horizontal resolution of 1 km and the observations are used to evaluate the performance of the model. The observations are also used to assess the katabatic flow coming from the glaciers Kronebreen and Kongsvegen. A strong impact of topography on the surface winds is conrmed by the numerical simulation and the observations, and the quality of the numerical simulations, both in wind speed and wind direction, is found to depend highly on the large scale wind direction. The largest errors in the model results for surface winds is found during northerly large scale flow, while the smallest errors is found when the large scale flow is in the same direction as the orientation of Kongsfjorden. The study supports the concept that the persistent ows out Kongsfjorden are of katabatic nature.

Session Number: P1l
Presenting Author: Tiina Kilpeläinen
Author Email: tiina.kilpelainen@unis.no
Author Affiliation: The University Centre in Svalbard
Co-Author: Timo Vihma and Haraldur Ólafsson
Co-Author Affiliation:
Abstract Title:
Modelling of spatial variability and topographic effects over Arctic fjords in Svalbard
Abstract:
The spatial variability of near-surface variables and turbulent surface fluxes was investigated in three Arctic fjords in Svalbard applying the mesoscale model weather research and forecasting (WRF). Ten real cases from winter and spring 2008, representing the most common large-scale flow directions, were simulated at 9, 3 and 1 km resolutions for 36 h each. Validation against tower observations and radiosoundings showed fairly good agreement, although a systematic warm and moist bias and slightly overestimated wind speeds were found close to the surface. The spatial variability within a fjord was large and it often reached levels comparable to the temporal variability. The spatial variability of the surface fluxes of sensible and latent heat was mostly controlled by the air and sea surface temperatures instead of wind speed. The same cases were also simulated without any topography over Svalbard. The topography increased the spatial variability but the influence on the mean values was not systematic, except that a clear warming effect was seen in all the fjords studied. The role of surface type increased with increasing air–sea temperature difference and was dominating over topographic effects for the air temperature, specific humidity and turbulent heat fluxes.

Session Number: P1m
Presenting Author: Haraldur Ólafsson
Author Email: haraldur68@gmail.com
Author Affiliation: University of Iceland, Icelandic Meteorological Office and Institute for Meteorological Research
Co-Author: Ole Edvard Grov, Jan Asle Olseth, Øystein Berentsen, Ólafur Rögnvaldsson, Hálfdán Ágústsson and Joachim Reuder
Co-Author Affiliation:
Abstract Title:
Fine-scale Observations and Simulations of the Atmosphere over Bergen, W-Norway
Abstract:
With increasing computing power, new opportunities emerge to reproduce and forecast weather and climate at fine spatial scales. This is particularly important in the vicinity of complex terrain, where the spatial variability of the state of the atmosphere close to the ground can be large. A new project within the framework of the Bergen School of Meteorology is emerging. This project includes the mounting of one lidar and 55 automatic weather stations in the Bergen (Bjørgvin) region at the west coast of Norway. The weather stations will serve to map the spatial variability of the atmosphere, not only for research and forecasting, but for education at all levels, and the data will be available online in real time. At the same time, high-resolution numerical simulations of the atmosphere over Bergen and its surroundings are performed in real time and the output is made available on the web. The data from the automatic weather stations and the numerical simulations is expected to be of great value for research of fine-scale features of the atmosphere in the future.

Session Number: P1n
Presenting Author: Marius Opsanger Jonassen
Author Email: Marius.Jonassen@gfi.uib.no
Author Affiliation: Geophysical Institute, University of Bergen Allegaten 70 5007 Bergen
Co-Author: Haraldur Ólafsson and Joachim Reuder
Co-Author Affiliation:
Abstract Title:
Simulations of the Bergen Orographic Shelter
Abstract:
The coast of W-Norway is very windy, yet the city of Bergen is relatively calm. Numerical simulations removing stepwise the mountains surrounding the city have been carried out to shed a light on the Bergen shelter. The simulations indicate that the Bergen shelter is a combination of a blocking effect and a wake effect from the mountains to the south and to the north of the city. The blocking effect is somewhat stronger than the wake effect, while the combined blocking and wake effects are less pronounced than the sum of the two.

Session Number: P1o
Presenting Author: Marius Opsanger Jonassen
Author Email: Marius.Jonassen@gfi.uib.no
Author Affiliation: Geophysical Institute, University of Bergen Allegaten 70 5007 Bergen
Co-Author: Joan Cuxart, Maria Antonia Jimenez, Haraldur Ólafsson, and Joachim Reuder
Co-Author Affiliation:
Abstract Title:
Thermally driven orographic winds over Southern France, simulated with MesoNH and WRF
Abstract:
Numerical simulations have been carried out using the weather prediction models MesoNH and the Weather Research and Forecasting model (WRF) for the field campaign Boundary-Layer Late Afternoon and Sunset Turbulence), to be performed during summer 2011 at Lannemezan, at the northern foothills of the Pyrenees. The chosen case study, 30 June -01 July, 2010, was dominated by a high pressure situation with weak pressure gradients thought to be climatologically typical for the period of the year and which fits with the focus of the BLLAST campaign. Under such conditions, thermally driven flow dominates in the form of upslope flows in a weakly stratified boundary layer during daytime and katabatic flows during a stably stratified boundary layer during nighttime. In the latter case, turbulence is typically very weak and the models’ forecast skills close to the ground level rely critically on surface parameterization schemes, which typically differ from model to model. The aim of this study is twofold. On one hand we seek to establish knowledge on typical flow patterns for the area of Lannemezan and the greater plain in the north under the described weather conditions. The results show interesting flow patterns in night time, set up by the two dominating mountainous structures in the area, the Pyrenees and Massif Central. Recommendations based on these results are also made for positioning of ground-based and airborne instrumentation in and near Lannemezan during BLLAST. Secondly, we compare the two models’ ability to accurately resolve observed temperature and humidity fields and the associated flow patterns against surface observations and satellite data.

Session Number: P1p
Presenting Author: Lorenzo Giovannini
Author Email: lorenzo.giovannini@ing.unitn.it
Author Affiliation: Atmospheric Physics Group, Department of Civil and Environmental Engineering, University of Trento. Via Mesiano 77, 38123 Trento, Italy.
Co-Author: Fei CHEN(1), Dino ZARDI(2), Massimiliano DE FRANCESCHI(3)
Co-Author Affiliation: (1) National Center for Atmospheric Research, Boulder, CO 80301, USA; (2) Atmospheric Physics Group, Department of Civil and Environmental Engineering, University of Trento. Via Mesiano 77, 38123 Trento, Italy.; (3) Atmospheric Physics Group, Department o
Abstract Title:
High-resolution numerical simulations of daily-periodic local circulations in Alpine valleys including urban environments
Abstract:
Daily-periodic local circulation systems in the Alpine Adige and Lakes valleys are investigated by means of high-resolution numerical simulations with the WRF model. A series of five nested domains is used, the inner one covering an area of about 100 x 100 km2 with a spatial resolution of 500 m.
In order to perform realistic simulations in complex terrain, a high resolution (30 m) topography dataset is utilized, while land use data are taken from the Corine Land Cover dataset, which has a spatial resolution of 100 m.
Simulations focus on summer fair weather days, when daily-periodic local circulation systems are well developed. The model output captures well the diurnal cycle of thermally driven circulations, as well as the interaction between the up-valley wind flowing in the Adige valley and the so-called Ora del Garda, a lake breeze originating on lake Garda shore, and reaching the Adige Valley through an elevated saddle north of Trento, after flowing along the Lakes Valley nearby. Results are compared with measurements from surface weather stations, whose data are analyzed in a companion work at this conference (Giovannini et al.).
The interactions between daily-periodic local circulation systems and the urban area of the city of Trento are also investigated. In particular the multi-layer Building Environment Parameterisation (BEP) scheme is utilized to evaluate the effects of the urban environment on temperature and wind fields. The parameters needed by the urban scheme were obtained from high resolution datasets of urban morphology, urban land cover and anthropogenic heat emissions, so as to represent the urban area thoroughly inside the model.

Session Number: P1q
Presenting Author: Jürg Schmidli
Author Email: jschmidli@env.ethz.ch
Author Affiliation: Institute for Atmospheric and Climate Science, ETH, Zurich
Abstract Title:
Large-eddy simulation of the daytime boundary layer evolution over an idealized valley
Abstract:
Thermally induced wind systems are ubiquitous over complex terrain and hence strongly influence the weather and climate in mountain regions. A recent valley wind model intercomparison study found large differences among nine mesoscale models in the local evolution of the valley wind system and in the vertical structure of the associated convective boundary layers. The different turbulence schemes employed by the nine models are thought to constitute one of the major sources of uncertainty. The turbulence schemes affect not only the temperature structure and heating in and above the valley, but also the evolution of the thermally induced winds and hence the mass exchange between the valley and the free atmosphere. Here we conduct large-eddy simulations of the daytime boundary layer over idealized valleys and compare them with corresponding coarse-resolution simulations in order to assess the impact of the representation of turbulent processes on the thermally induced winds, local boundary layers and on the heating of the valley atmosphere.

Session Number: P1r
Presenting Author: Bogdan Rosa
Author Email: bogdan.rosa@imgw.pl
Author Affiliation: Institute of Meteorology and Water Management
61 Podlesna St, Warsaw 01-673, Poland
Co-Author: Marcin Kurowski, Michał Ziemiański
Co-Author Affiliation: Institute of Meteorology and Water Management
Abstract Title:
High-resolution anelastic modeling of Alpine flows: a case study for a summer convection
Abstract:
Horizontal grid size of contemporary numerical weather prediction (NWP) models is systematically increasing and is currently approaching 1km. The higher resolution allows for a better representation of simulated flows, including specifically mountain effects. Additionally, such a grid resolution allows the NWP models to enter the regime of explicit representation of moist convective processes. All these, in turn, require more sophisticated numerical techniques for reliable and robust modeling of such flows over more and more complex terrain, as well as appropriate coupling between the dynamical core and the physical parameterizations. In this context, it is interesting to explore the models capability for representing convective processes influenced by complicated Alpine orography.
The presentation shows the results of numerical simulations of a summer Alpine convection in the regime of weak external forcing. The experiments were performed using the anelastic nonhydrostatic EULAG model, developed in the National Center for Atmospheric Research (NCAR), a prospective candidate for the dynamical core of a future operational weather prediction model. The simulations employ different simplified representations of the boundary layer physics, including the boundary layer attenuation, Fickian diffusion and turbulent kinetic energy (TKE) parameterization, as well as simple parameterizations of moist processes. The study is focused especially on exploring the influence of horizontal grid resolution on the simulated convective processes.

Session Number: P1s
Presenting Author: Wolfgang Langhans
Author Email: wolfgang.langhans@env.ethz.ch
Author Affiliation: Institute for Atmospheric and Climate Science, ETH Zurich
Co-Author: Susanne Bieri, Jürg Schmidli, Christoph Schär
Co-Author Affiliation: Institute for Atmospheric and Climate Science, ETH Zurich
Abstract Title:
Observations and numerical simulations of Alpine pumping and its interaction with moist convection
Abstract:
Differential heating between Alpine valleys and the adjacent foreland induces a complex and multi-scale system of mass, heat, and moisture transport. The formation of up-valley (daytime) and down-valley (nighttime) wind-systems is frequently observed during flat-pressure distributions in summer and commonly referred to as Alpine pumping. This plain-to-mountain circulation induces horizontal convergence within the PBL which needs to be compensated by vertical motion. Still, the link to the formation of deep convection is less obvious and remains a controversial issue. Recent studies have been suggesting that an initiation of deep orographic convection might not directly be related to mountain-scale convergence, and the associated cold-air advection might even reduce the local potential for convective initiation.
The aim of this study is to quantify Alpine pumping and its interaction with convection for one particular summer-month characterized by pronounced thermally-driven Alpine circulations and deep convection. For this purpose, surface-based and remote-sensing observational data are studied together with convection-permitting numerical simulations covering the whole Alpine arc. The latter are conducted using the COSMO-CLM model at convection-permitting resolutions (2.2 an 1.1 km). The numerical results have been validated against the observations in a first part of this study. The physics of the interaction will be studied in a second part.
We find that COSMO-CLM is capable of representing the overall diurnal evolution of surface radiation, horizontal pressure gradient, anabatic wind, cloud development and convective precipitation. The grid-spacing reveals to have little impact on the overall evolution of Alpine pumping and the formation of precipitation. Compared to a convection-parameterizing simulation (6.6 km), both convection-permitting simulations realize a more accurate onset of deep convection. Still, the evaluation of COSMO-CLM at kilometer-scales reveals deficits in modeling the transition between shallow and deep convection and nighttime cloudiness.
Concerning the second part, first results of an Alpine-scale analysis indicate a peak of mass convergence slightly before deep convection is strongest. Divergence starts soon after the diurnal precipitation maximum has been reached. This might suggest the favoring of orographic convection due to the prevailing convergence and could explain the transition to divergent flow as a consequence of cold-air pooling. Enhancement of our understanding of this interaction is expected from studying its day-to-day variability and from numerical experiments specifically addressing the importance/existence of this link.

Session Number: P1t
Presenting Author: Alexandre Paci
Author Email: alexandre.paci@meteo.fr
Author Affiliation: CNRM-GAME, URA1357 Meteo-France/CNRS, Toulouse, France
Co-Author: E.R. (Ted) Johnson, J.G. (Gavin) Esler, L. Lacaze, N. Boulanger, O.Eiff
Co-Author Affiliation: Department of Mathematics, University College London, London, U.K.,IMFT, CNRM-GAME, Institut de Mécanique des Fluides de Toulouse, CNRS INPT and Université de Toulouse III, Toulouse, France
Abstract Title:
Orographic drag and lee wave breaking: two recent experiments carried in the CNRM-GAME stratified water tank
Abstract:
The geophysical fluid dynamics laboratory of the French meteorological service research center ( CNRM-GAME, URA1357 Meteo-France and CNRS ) provides unique facilities for fundamental and applied study of homogeneous, stratified and/or rotating flows. The research activities of the team focus on atmospheric boundary layers and internal gravity waves. Two recent experiments related to topographic internal waves are presented here. The CNRM-GAME stratified water flume is a unique facility to study neutral or stratified flows ( e.g. [1] and [2] ). It has been specially designed to generate accurate and exhaustive datasets on flows similar to the atmospheric or oceanic ones under perfectly controlled conditions. It is thus a good extension of field experiments limited by the fact that data are scattered and conditions are not well controlled. This 30 m long, 3 m wide and 1.6 m deep density-stratified water flume can also be operated as a towing tank filled with water or with density-stratified brines. Experiments have been recently carried out in order to investigate two inter-related aspects of flow over orography: the structure of the flow-field and the pressure drag exerted on the oncoming flow ( see [3] and [4] ). The later is of particular importance to oceanographers, climate modelers and researchers involved in the development of numerical weather prediction models, because of the need to parameterize the drag exerted by orography with spatial scales below the model grid scale. Results are expected to validate experimentally a theoretical model which predicts the structure
of internal waves and the drag exerted by a mountain on the atmosphere from a small set of parameters. Another recent set of experiments extends previous laboratory work ( e.g. [5] ) on lee wave breaking. Progress in measurement techniques allowed to study in the laboratory for the first time the development of toroidal structures. These structures result from instabilities of the initial quasi-2D vortex parallel to the mountain axis. [1] Steeneveld G.-J., D. Dobrovolschi, A. Paci, O. Eiff, L. Lacaze and A.A.M. Holtslag

(2010) : Sensing the stable boundary layer in a towing tank, 19th Symposium on Boundary Layers and Turbulence, Keystone CO (USA), August 2-6,
2010 ( available at http://ams.confex.com/ams/pdfpapers/172503.pdf ). [2] Knigge C., D. Etling, A. Paci and O. Eiff (2010): Laboratory experiments on mountain-induced rotors. Q. J. R. Meteorol. Soc. 136: 442–450. ( available at
http://dx.doi.org/10.1002/qj.564 ) [3] Johnson E.R., J.G. Esler, A. Paci, S. Cazin, E. Cid, O. Eiff and L. Lacaze (2010): Near-critical orographic forcing of stratified flow. In Proceedings of the HYDRALAB III Joint Transnational Access User Meeting (editors Joachim Gruene and Mark Klein Breteler), Hannover, 2nd-4th February 2010, pp. 207-210, ISBN- 987-3-00-030141-4 ( available at http://www.hydralab.eu/proceedings/CNRS- 21_Johnson.pdf ).
[4] Cid E., L. Lacaze, S. Cazin, A. Paci and O.Eiff (2010) : Mesure d'ondes à l'interface d'un bi-couche par stereo correlation d'images, Congres Francophone de Techniques Laser, CFTL 2010, Vandoeuvre-les-Nancy, 14-17 septembre 2010 ( available at https://roquefort.nancy -universite.fr/CONGRES/DVDCFTL/PAP/PAP_CID15-06_005.pdf ). [5] Eiff O., F. Huteau and J. Tolu (2005): High-Reynolds-number orographic wave-breaking experiments. Dyn. Atmos. Oceans 40: 71–89 ( available at http://dx.doi.org/10.1016/j.dynatmoce.2004.10.016 ).

Session Number: P1u
Presenting Author: Uros Strajnar
Author Email: uros.strajnar@gov.si
Author Affiliation: Environmental Agency of the Republic of Slovenia, Vojkova, 1/b, 1000 Ljubljana, Slovenia
Abstract Title:
Forecasting Extreme Precipitation : Northwestern Slovenia Event from 21 to 26/12/2009
Abstract:
December 2009 was marked with extreme variations in weather and highest ever measured 5 days differences of maximum temperatures. It started with maximum temperature not higher than -5 deg C on 20/12/2009 and more than 15 cm of snow in the valleys and finished with unseasonably warm and humid period with maximum temperature more than 15 deg C. From 21 to 26/12/2009 the main cause of precipitation was strong southwesterly wind producing orographicaly induced precipitations. In many locations historical extremes of precipitation accumulations were measured. Comparing to many other extreme events in this region producing flash floods in just several hours of rainfall with maximum measured precipitation rates up to 70 mm per hour (e.g.18/9/2007, Zelezniki case), this time the hourly precipitation rates were much lower reaching not more than 15 mm per hour. This is due to the fact that the air mass was less potentially unstable because the event happened at the end of December and the Adriatic Sea sea surface temperature was not more than 11 deg C.
The selected case is important as one of the reference ones because the state of the atmosphere was well predictable. Almost all operationally available medium range (ECMWF, DWD, NCEP) and meso-models (ALADIN) gave reliable forecasts regarding the timing and extent of precipitation. Even in the ECMWF ensemble forecast from 16/12/2009 0 UTC run a significantly number of members forecasted extreme precipitation episode with very pronounced advection of warm and humid air. In the subsequent forecasts the signal remained.
Because the signal of extreme weather was still present and persistent on 23/12/2009 National Meteorological Service of Slovenia issued red alert for the area according the MeteoAlarm scale for the extreme precipitation from 150 mm to 300 mm during the next 3 days. On 25th of December the maximum 24h amount of 247 mm was measured in Kobarid, and the biggest 5 days accumulation of 611 mm at Vogel. Extreme precipitation accumulation together with fast snow melting resulted in 2200 m3/s vs 100 m3/s which is some of highest discharge values of Soča River in 65 years of measurements. This caused extensive floods and major land-slides.
The selected case shows the potential of in medium range synoptic forecasting extreme situations. Because of consistent and timely precise forecast 5 days in advance and given the fact that this convective precipitation were not so intense there was no casualties and the damage cost was also reduced.

Session Number: P1v
Presenting Author: Balram Ambade
Author Email: bambade@gmail.com
Author Affiliation: School of Studies in Chemistry, Pt Ravishankar Shukla University Raipur CG, 492010, India
Co-Author: Litrupa Ambade
Co-Author Affiliation: Govt. Girls College Durg, CG, India
Abstract Title:
Studies of acid rain pollution and their harmful consequence on livelihood
Abstract:
Acid rain is a rain or any other form of precipitation that is unusually acidic, i.e. elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals, and infrastructure through the process of wet deposition. Acid rain is caused by emissions of sulfur dioxide and nitrogen oxides which react with the water molecules in the atmosphere to produce acids. The chemical composition of rainwater precipitated at two industrialized locations of central India i.e. Raipur and Korba during monsoon period of year, 2008 is described. The physico-chemical characteristics i.e. pH, conductivity, TDS, Cl-, NO3-, SO42-, NH4+, Na+, K+, Mg2+, Ca2+, Fe, Mn, Cu, Zn, Pb and Hg of the rainwater was reported. The volume weighted mean (VWM) pH value at Raipur (n = 31) and Korba (n = 11) was 6.4 and 4.9, respectively. The sum of total VWM value of 14 species (i.e. Cl-, NO3-, SO42-, NH4+, Na+, K+, Mg2+, Ca2+, Fe, Mn, Cu, Zn, Pb and Hg) in the rainwater of Raipur and Korba was 20.0 and 24.1 mg l-1, respectively. The VWM value for Cl-, NO3-, SO42-, NH4+, Na+, K+, Mg2+, Ca2+, Fe, Mn, Cu, Zn, Pb and Hg at Raipur was 3.50, 2.71, 7.95, 0.73, 1.00, 0.92, 1.1, 2.53, 0.13, 0.29, 0.12, 0.16, 0.17 and 0.004 mg l-1, respectively. The variations, scavenging and enrichment, correlation and source of the chemical species in the rainwater are discussed.
Keywords: The physico-chemical characteristics, variations, enrichment, correlation

Session Number: P2a
Presenting Author: Ivana Stiperski
Author Email: stiperski@cirus.dhz.hr
Author Affiliation: Meteorological and Hydrological Service of Croatia,
Zagreb, Croatia
Co-Author: Vanda Grubišić
Co-Author Affiliation: University of Vienna, Austria
Abstract Title:
Aircraft observations of complete destructive interference during T-REX
Abstract:
Lee wave resonance is expected for trapped lee waves over double ridges. Depending on the ratio of ridge separation distance to the horizontal trapped lee wave wavelength, constructive or destructive interference develops, leading to the enhancement or reduction of wave amplitude in the lee of a double obstacle. Numerical simulations show that complete destructive interference, for which waves in the lee of a double ridge nearly completely cancel out, is possible for a downstream ridge lower than the upstream one. This terrain configuration is characteristic of Owens Valley, California, where the downstream Inyo range is lower than the upstream Sierra Nevada. Owens Valley, a site famous for its large amplitude trapped lee waves and rotors, was the location of the Terrain-induced Rotor Experiment (T-REX). According to the idealized two-dimensional numerical simulations with upstream conditions and orography characteristic of the T-REX environment, complete destructive interference develops under specific conditions resulting in amplitudes of waves and rotors over Owens Valley being significantly larger than those in the lee of the Inyo range. The numerical results also show that, irrespective of flow nonlinearity and surface friction, the ratio of wave amplitudes in the lee of two ridges is approximately constant.
In this study we examine in situ data collected by research aircraft during T-REX for evidence of complete destructive interference in the lee of the Inyo range. Wave amplitudes and horizontal wavelengths of the lower tropospheric waves are determined using data collected by the University of Wyoming King Air and the FAAM BAe-146 aircraft from a number of T-REX missions, This data is compared to the numerical results obtained for complete destructive interference, in particular as it pertains to the amplitude ratio and wave phase characteristics that are responsible for the occurence of complete destructive interference. Preliminary results show wave cancellation in the lee of the Inyo range during several T-REX research flights, in accordance with the numerical modeling results.

Session Number: P2b
Presenting Author: Guðrún Nína Petersen
Author Email: gnp@vedur.is
Author Affiliation: Icelandic Meteorological Office, Reykjavík, Iceland
Co-Author: Ian A. RENFREW (1), G. W. K. MOORE (2)
Co-Author Affiliation: (1) School of Environmental Sciences, University of East Anglia, Norwich, UK, (2)Department of Physics, University of Toronto, Toronto, Ontario, Canada
Abstract Title:
Cold barrier winds off southeastern Greenland during the Greenland Flow Distortion experiment
Abstract:
During the Greenland Flow Distortion experiment, barrier flow was observed by an instrumented aircraft on 1, 2, 5 and 6 March 2007 off southeastern Greenland. During this time period the barrier flow increased from a narrow jet, ∼15 m/s, to a jet filling almost the whole of the Denmark Strait with maximum wind speed exceeding 40 m/s. Dropsonde observations show that the barrier flow was capped by a sharp temperature inversion below mountain height. Below the inversion was a cold and dry jet, with a larger northerly wind component than that of the flow above, which was also warmer and more moist. Thus, the observations indicate two air masses below mountain height: a cold and dry barrier jet of northern origin and, above this, a warmer and moister air mass that was of cyclonic origin.
Numerical simulations emphasize the non-stationarity of the Greenland barrier flow and its dependence on the synoptic situation in the Greenland–Iceland region. They show that the cold barrier jet originated north of the Denmark Strait and was drawn southward by a synoptic-scale cyclone, with the strength and location of the maximum winds highly dependent on the location of the cyclone relative to the orography of Greenland. Experiments without Greenland\'s orography suggest a 20 m/s enhancement of the low-level peak wind speeds due to the presence of the barrier.
These cases indicate that the Greenland barrier flows are not classic geostrophically balanced barrier flows but have a significant ageostrophic component and are precisely controlled by synoptic-scale systems.

Session Number: P2c
Presenting Author: Alexander Gohm
Author Email: alexander.gohm@uibk.ac.at
Author Affiliation: Institute of Meteorology and Geophysics, University of Innsbruck, Innrain 52, A-6020 Innsbruck, Austria
Co-Author: Veronika Schreiner *, Martin Hagen **
Co-Author Affiliation: *) Meteomedia, Switzerland; **) DLR Oberpfaffenhofen, Germany
Abstract Title:
What caused the change in the convection regime on two consecutive COPS days?
Abstract:
During the IOP 15 of the Convective and Orographically induced Precipitation Study (COPS) a change in the convection regime was observed from 12 to 13 August 2007. On the first day, convective cells formed above the Vosges mountains and remained stationary, whereas on the second day, cells where triggered to the lee of the ridge in the adjacent Rhine Valley and traveled further downstream. In a previous study it was hypothesized that this regime change was associated with an increase in the dry Froude number from below to above unity that caused a shift in the convergence zone from above the crest to the lee.
Using high-resolution numerical simulations with the Weather Research and Forecasting (WRF) model we confirm previous findings that on the first day convection was initiated by thermally induced upslope flows as a result of surface layer heating above the elevated terrain. Background winds were not strong enough to significantly displace the convective cells. With the increase in background wind speed from the first to the second day, the locations of convective initiation shifted to the lee. The numerical model simulates cells to be dynamically triggered by forced lifting due to a hydraulic-jump like feature that forms to the lee at the air mass boundary between the descending and potentially warmer downslope flow and the nearly stagnant and potentially cooler air in the Rhine valley.
A closer inspection of the model results indicates that convective initiation on the second day did not occur downstream of mountain gaps, as hypothesized in a previous study, but rather to the lee of individual mountain peaks. It appears that the highest peaks deflected the impinging flow in a way to promote convergence to their lee. This convergence was enhanced by the above mentioned hydraulic jump.

Session Number: P2d
Presenting Author: Lukas Tüchler
Author Email: lukas.tuechler@univie.ac.at
Author Affiliation: University of Vienna, Department of Meteorology and Geophysics, Althanstraße 14/UZA II, 1090 Vienna, Austria
Co-Author: Niko Filipović, Reinhold Steinacker
Co-Author Affiliation: University of Vienna, Department of Meteorology and
Abstract Title:
Comparison between gauge and radar precipitation measurements in high spatial and temporal resolution during COPS
Abstract:
During the field phase of the COPS campaign (Convective and Orographically induced Precipitation Study) from June to August 2007, the Department of Meteorology and Geophysics of the University of Vienna operated a network of one hundred automatic weather stations (AWS) of the type HOBO. The stations were arranged in a nearly regular grid with an average spacing of one kilometre. The network was located in the southwest of Germany in an area of complex topography (Black Forest), in the eastern part of the COPS domain. The AWS were equipped with sensors for measuring temperature, humidity, pressure and wind with a temporal resolution of one minute as well as a tipping bucket rain gauge to measure precipitation. Precipitation measurements were logged event-based with a resolution of 0.2mm and accumulated to one minute data. This ground-based data with high spatial and temporal resolution is supplemented with measurements of two C-band weather radars: operational radar of the German weather service (DWD) and the research radar of the Karlsruhe Institute of technology (KIT) situated in Türkheim and near Karlsruhe respectively. The radar precipitation product has a temporal resolution of five minutes and a spatial resolution of 500 meters. These two weather radars are located about 70km southeast (Türkheim) and 60km northwest (Karlsruhe) of the AWS-network.
Due to the location of the AWS-network between the two radars, the overlapping scanning allows to detect the precipitation over the moderate complex topography of the AWS network very well. For selected dates (COPS IOPs) with different types of precipitation (stratiform, convective), comparisons between radar and gauge measurements as well as comparisons between precipitation measurements of the two radars were conducted. Correlation between the precipitation measurements of the two radars and between radar and gauge measurements is calculated to investigate the spatial and temporal agreement of the different measuring devices. Beam shielding of the lowest two elevations occurs for one of the radars over the AWS network area – using gauges and the second radar the effect of the beam shielding on precipitation estimation is investigated.

Session Number: P2e
Presenting Author: Fumiko Aoshima
Author Email: Fumiko.Aoshima@uni-hohenheim.de
Author Affiliation: University of Hohenheim, Institute of Physics and Meteorology
Co-Author: Hans-Stefan Bauer, Andreas Behrendt, Volker Wulfmeyer
Co-Author Affiliation: University of Hohenheim, Institute of Physics and Meteorology
Abstract Title:
Characteristics of precipitation and wind fields within the COPS domain depending on different forcing conditions
Abstract:
The COPS (Convective and Orographically-induced Precipitation Study) field campaign was performed from June 1 to August 31, 2007, in south-western Germany and eastern France covering the Vosges mountains, Rhine valley, and the Black Forest mountains. We categorised each day according to one of the following three forcing conditions: strongly forced, weakly forced, and air mass convection. For the categorisation, we used Meteosat-8 satellite images (combination of visible and IR channels) and weather charts (analysis of Deutscher Wetterdienst, DWD). The VERA (Vienna Enhanced Resolution Analysis) provides precipitation and wind fields with 8 km and 1 hour resolution for all COPS days. In addition to these data, we used the radar precipitation composite of DWD which has a resolution of 2.8 km and 5 minutes. For all 92 COPS days depending on the forcing category, we analysed the precipitation and wind data within 4 areas, namely, the Vosges mountain area, the Rhine valley area, the Black Forest area, and the full COPS region. At the conference, we will present the results of this analysis. For example, the diurnal cycle of precipitation showed different features in the different months of the COPS campaign. While in July there was a clear maximum shortly after local noon (1130 UTC) for precipitation related to air mass convection, there was no clear diurnal cycle for June and August. Most precipitation was found in the analysis for strongly forced conditions, less for weakly forced conditions and air mass convection; there was most precipitation in the Black Forest area for all three forcing conditions during the COPS period, and more in the Vosges than in the Rhine valley.

Session Number: P2f
Presenting Author: Jeremy Price
Author Email: jeremy.price@metoffice.gov.uk

Author Affiliation: UK Met Office, Met Office Research Unit, Cardington Airfield
Shortstown, Bedfordshire, MK42 0SY
Co-Author: Volker Horlacher, Fay Davies
Co-Author Affiliation: UK Met Office, University of Leeds, UK
Abstract Title:
The Structure of Cold Pools in the Presence of Partial Cloudiness
Abstract:
Data are presented from a recent field campaign conducted in 2009-10 to examine cold-pooling of air in a region of small hills, Shropshire UK (COLPEX). Hill to valley heights are typically 50-150m and valley widths 1-3km in this region. Data collected from instrumented masts, radiosondes and a Doppler lidar have been used to examine the evolution and structure of cold air pooling in the valley bottoms in conditions of partial cloudiness. Assessing the sensitivity of cold-pool structure to these conditions will help inform requirements for their successful prediction in computer models.
It is found that when cold pools form under clear skies, they can quickly erode/ disappear within 1-2 hours when low cloud advects over the region. Furthermore, it is found that a cold pool can quickly re-form if the cloud subsequently clears or thins sufficiently. Data are presented to show a case where this occurred when two different cold pools formed during one night, separated by a cloudy period. Geographical variations in cloud amount at different locations in the region are examined, and the effect on cold-pools discussed.

Session Number: P2g
Presenting Author: Bradley Jemmett-Smith
Author Email: b.jemmett-smith@see.leeds.ac.uk

Author Affiliation: University of Leeds
Co-Author: Dr Andrew Ross
Co-Author Affiliation: University of Leeds
Abstract Title:
Flow characteristics in moderate terrain; results from the COLPEX field campaign
Abstract:
Cold air pooling over complex terrain are a well documented meteorological phenomenon, characterised by a temperature inversion, forming soon after sunset during clear calm conditions and decaying soon after sunrise. The temperature differences can be very large over relatively small scales. Associated with this phenomenon are a number of hazards, including fog, frost and pollution episodes. Currently there are a number of uncertainties associated with the occurrence of these cold air pooling events and as such there are particular problems related to forecasting their occurrence, strength and location. Some emphasis of the results shown here will be on discovering whether cold air pool formation in moderate terrain is dominated by one of two mechanisms; katabatic flows (cold drainage flows) or in-situ cooling, both of which are products of radiative cooling at the surface following sunset.

Session Number: P2h
Presenting Author: Vanda Grubišić
Author Email: Vanda.Grubisic@univie.ac.at
Author Affiliation: University of Vienna, Department of Meteorology and Geophysics
Co-Author: Johannes Sachsperger; Rui Caldeira
Co-Author Affiliation: University of Vienna, Austria; Center of Marine and Environmental Research, Portugal
Abstract Title:
The atmospheric wake of Madeira Island: i-WAKE Campaign
Abstract:
The 57 km long and 22 km wide NW-SE oriented island of Madeira lies in the western Atlantic, 950 km SW from the southern tip of Portugal. The highest island peak, Pico Ruivo, reaches 1862 m above sea level (ASL). Due to its size, atmospheric stability structure and winds upstream, wake formation in the downstream region of this mountainous island is expected, in particular in summer when the most sustained winds below the trade wind inversion come from NE, the direction perpendicular to the island orientation.
In situ and remote sensing measurements were obtained during the i-WAKE airborne campaign (Aug-Sep 2010) in Madeira. SAFIRE’s ATR 42 research aircraft collected data both upstream and downstream of the island. Presented herein will be the first documented data analysis of the Madeira’s atmospheric wake from a number of i-WAKE missions, combining meteorological in situ data, remote sensing data and attendant WRF simulations. The i-WAKE results will be discussed in relation to previous laboratory and numerical experiments as well as theoretical characterizations of the atmospheric wake phenomena.

Session Number: P2i
Presenting Author: Amélie Kirchgaessner
Author Email: amelie.kirchgaessner@bas.ac.uk
Author Affiliation: British Antarctic Survey, High Cross, Madingley Road
Cambridge, CB30ET
Co-Author: Dr John King (1), Dr Tom Lachlan-Cope (1), Dr Phil Anderson (1), Dr Victoria Smith (2), Andrew Elvidge (3)
Co-Author Affiliation: (1)British Antarctic Survey, (2) University Leeds, (3) University of East Anglia
Abstract Title:
Orographic Flow across the Antarctic Peninsula - a case study
Abstract:
The project OFCAP investigates how the circumpolar westerly winds around Antarctica interact with the orographic barrier formed by the mountains of the Antarctic Peninsula, and how this interaction influences the regional climate.
It has been shown that circumpolar Westerlies have increased in strength and frequency over the past decades. This increases in turn the occurrence of Föhn events on the lee (eastern) side of the Peninsula, leading to the extreme warming that has been observed over the last 30 or so years. This warming is thought to have contributed to the collapse of parts of the Larsen Ice Shelf in 1995 and 2002.
During the Antarctic season 2010/11 a comprehensive field campaign took place comprising of measurements from specifically deployed weather stations on a transect along 67°S, measurements using the MASIN aircraft operated by the British Antarctic Survey, radiosonde launches at research station Rothera and from a camp on the Larsen Ice Shelf, and surface energy balance measurements on the Larsen Ice Shelf. Thus OFCAP has produced a valuable data set of meteorological parameters from the surface up to ~3000m between approximately 66°S and 68°S and from 70°W to 61°W.
The presentation will describe in detail one event of westerly flow across the Peninsula captured during this field campaign. The presentation will briefly show its synoptic development, and then characterise the Föhn event using data from radiosonde ascents, weather stations and aircraft measurements made on either side of and over the Antarctic Peninsula. The data illustrates the strong effect such Föhn events show over the Larsen Ice Shelf and thus may have on its stability.

Session Number: P2j
Presenting Author: Victoria Smith
Author Email: v.smith@see.leeds.ac.uk
Author Affiliation: Institute for Climate and Atmospheric Science, University of Leeds, Leeds, UK
Co-Author: Alan Gadian; Stephen Mobbs; Tom Lachlan-Cope; Russell Ladkin; Andrew Elvidge
Co-Author Affiliation: National Centre for Atmospheric Science; National Centre for Atmospheric Science; British Antarctic Survey; British Antarctic Survey; University of East Anglia
Abstract Title:
Preliminary analysis and observations of gravity wave development above the Antarctic Peninsula during the Orographic Flows and the Climate of the Antarctic Peninsula (OFCAP) field project
Abstract:
Circumpolar westerly winds that dominate the flow around Antarctica are known to provide favourable conditions for orographically-generated gravity waves when they encounter the high mountains of the Antarctic Peninsula. Downslope winds associated with these gravity waves are thought to impact the climate of the ice shelves east of the Peninsula, through the removal of low level clouds and very cold continental air masses. As part of the Orographic flows and the Climate of the Antarctic Peninsula (OFCAP) field project, observations of gravity waves have been made in cross-peninsula flow at 67 degrees south, using an instrumented Twin Otter aircraft. Preliminary analysis of two case studies will be presented. One case where a critical level was observed and one where the wave propagated above the altitude to which the plane could ascend. Both aircraft and radiosonde profiles will be used in addition to high resolution (1.5 km) simulations using the Weather Research and Forecasting (WRF) numerical model to investigate the development of the two wave regimes.

Session Number: P2k
Presenting Author: Haraldur Ólafsson
Author Email: haraldur68@gmail.com
Author Affiliation: University of Iceland, Icelandic Meteorological Office and Institute for Meteorological Research
Co-Author: Marius Opsanger Jonassen, Hálfdán Ágústsson, Ólafur Rögnvaldsson, Dubravka Rasol, Joachim Reuder, Sigurður Jónsson and Bjarni G. P. Hjarðar
Co-Author Affiliation:
Abstract Title:
The MOSO experiment
Abstract:
During the summer of 2009, fine-scale observations of the atmosphere were carried out in the vicinity of the complex terrain at the coast of SW-Iceland. The observations were made with the aid of 6 mobile and 15 more permanent automatic weather stations, unmanned model aircrafts (SUMO), making profiles of the lower troposphere and 9 microbarographs. In addition, radiosoundings from Keflavik (WMO 04018) are available every 12 hours. The MOSO dataset includes detailed observations of the sea breeze, downslope flow, blockings and wakes in four dimensions. Examples are given of observations of the onset of the sea breeze in the mountain-surrounded basin of SW-Iceland and a weak downslope windstorm.

Session Number: P2l
Presenting Author: Hálfdán Ágústsson
Author Email: halfdana@hi.is
Author Affiliation: University of Iceland, Icelandic Meteorological Office and Institute for Meteorological Research
Abstract Title:
Simulations and measurements of atmospheric icing in mountains
Abstract:
This study compares observed icing in a test span in complex orography at Hallormsstaðaháls (575 m) in East-Iceland with parameterized icing based on an icing model and dynamically downscaled weather at high horizontal resolution. Four icing events have been selected from an extensive dataset of observed atmospheric icing in Iceland. A total of 86 test-spans have been erected since 1972 at 56 locations in complex terrain with more than 1000 icing events documented. The events used here have peak observed ice load between 4 and 36 kg/m. Most of the ice accretion is in-cloud icing but it may partly be mixed with freezing drizzle and wet snow icing. The calculation of atmospheric icing is made in two steps. First the atmospheric data is created by dynamically downscaling the ECMWF-analysis to high resolution using the non-hydrostatic mesoscale Advanced Research WRF-model. The horizontal resolution of 9, 3, 1 and 0.33 km is necessary to allow the atmospheric model to reproduce correctly local weather in the complex terrain of Iceland. Secondly, the Makkonen-model is used to calculate the ice accretion rate on the conductors based on the simulated temperature, wind, cloud and precipitation variables from the atmospheric data. In general, the atmospheric model correctly simulates the atmospheric variables and icing calculations based on the atmospheric variables correctly identify the observed icing events, but underestimate the load due to too slow ice accretion. This is most obvious when the temperature is slightly below 0°C and the observed icing is most intense. The model results improve significantly when additional observations of weather from an upstream weather station are used to nudge the atmospheric model. However, the large variability in the simulated atmospheric variables results in high temporal and spatial variability in the calculated ice accretion. Furthermore, there is high sensitivity of the icing model to the droplet size and the possibility that some of the icing may be due to freezing drizzle or wet snow instead of in-cloud icing of super-cooled droplets. In addition, the icing model (Makkonen) may not be accurate for the highest icing loads observed.

Session Number: P2m
Presenting Author: Christof Gromke
Author Email: gromke@slf.ch
Author Affiliation: WSL Institute for Snow and Avalanche Research SLF,
Flueelastr. 11, 7260 Davos Dorf, Switzerland
Co-Author: Michael Lehning
Co-Author Affiliation: WSL Institute for Snow and Avalanche Research SLF, Flueelastr. 11, 7260 Davos Dorf, Switzerland
Abstract Title:
Eddy covariance measurements at a snow covered alpine site in Davos/Switzerland
Abstract:
An eddy covariance (EC) system for measuring vertical fluxes of sensible and latent heat over snow was set up in summer 2011 at the Weissfluhjoch field site (2450 m a.s.l.) close to Davos/Switzerland for continuous operation. The EC system consists of an open path infrared gas analyzer (model LI-7500A) and a 3D ultrasonic anemometer (model Kaijo Denki DAT-310 with probe TR-61C). The final objective is to study the air-surface exchange of sensible and latent heat and relate it to near surface layer snow pack properties (e.g. grain form, grain size) and to the snow pack mass balance. The particular interest will be in gathering information on foot-print and atmospheric stability influences on flux measurements and model formulations for surface exchange in complex terrain over snow.
Here we present a primarily methodological study analysing the effect of different measurement data processing methods and flux calculation approaches on the sensible and latent heat flux estimates. The analysis is based on the EC data collected within approximately 5 months of the winter season 2010/2011. In particular, we investigate the effect of (i) criteria for well developed turbulence and steady state conditions, (ii) despiking, detrending and spectral correction algorithms, (iii) the length of the averaging period, (iv) the tilt correction method, i.e. double rotation or planar fit method and (v) the WPL correction on the resulting flux estimates at our specific alpine site.
The motivation for the methodological study comes from the fact that most studies of this type have been performed for bare or vegetated soil surfaces in homogeneous terrain at low altitude sites in moderate and warm climates rather than for snow covered surfaces in cold alpine terrain. However, due to considerable differences in ambient conditions between these types of sites, it appears advisable to pursue a critical analysis of the effect of different data processing and calculation approaches on flux estimates and to establish specific rules for such sites. The findings of this analysis are moreover considered to be particularly beneficial and generally applicable to EC measurements and flux estimates over snow covered surfaces in cold climates at high altitude sites or in polar terrain. The complication of the complex terrain will also be addressed, although generalization may be much more difficult in this case.

Session Number: P2n
Presenting Author: Christine Groot Zwaaftink
Author Email: groot@slf.ch
Author Affiliation: WSL Institute for Snow and Avalanche Research SLF
Davos, Switzerland
Co-Author: K.C. Leonard, R. Meister, D. Lussi, M. Lehning
Co-Author Affiliation: WSL Institute for Snow and Avalanche Research SLF
Abstract Title:
High frequency measurements of intermittent drifting snow mass flux under gusty conditions
Abstract:
Drifting snow has long been known to significantly influence snow distribution in the Alpine region. A variety of model formulations exist, some of which can replicate the spatial distribution of snow on the scale of a few meters. However, to understand and predict finer scales of snow distribution, the drifting snow process must be better understood, requiring measurements of drifting snow mass flux profiles.
We present results from a winter 2011 experiment comparing drifting snow measurement devices and their resulting mass flux profiles at the Weissfluhjoch Versuchsfeld (2540 m.a.s.l., near Davos, Switzerland). The experiment took place on a gentle ridge slightly downwind from the Versuchsfeld flat field and included several masts on which we obtained mass flux profiles over 2 meters height with a) 4 photoelectric particle counters, b) 2 FlowCapt impact sensors, and c) 4 Mellor or “rocket” traps, which were sampled at irregular intervals. In addition to these snow transport profiles, we measured 2 meter profiles of the wind speed, air temperature and humidity.
We report here on two drifting snow events lasting 2 hours each. Both were preceded by a snowfall period. Analysis of both events shows a similarly rapid increase in mass flux with increasing wind speed in the saltation layer. Interestingly, mass fluxes averaged over 15 minutes are up to 12 times larger than predicted by existing saltation models. Possible causes of this include speed-up effects over the gentle ridge and a non-equilibrium transport situation. Another explanation may be the highly intermittent character of the observed drifting snow, which is poorly represented by continuum models. When calculating transport rates using peak gust speeds rather than mean wind speeds over 2 minutes intervals, our results were in better agreement with model predictions. The intermittent nature of the observed drift is also demonstrated by results from the particle counters: we record the total number of particles over 10 seconds as well as the maximum number of particles during 1 second within this 10 second period. During drift events, the ratio between the maximum number of particles during 1 second to the total number of particles in 10 seconds has a mean value of 37% but can be up to 100%. This shows that extremely short gusts of wind can be responsible for a substantial fraction of the total snow transport during longer intervals in the storm period.

Session Number: P2o
Presenting Author: Sigurður Jónsson
Author Email: sj@vedur.is
Author Affiliation: University of Iceland and the Icelandic Meteorological Office
Co-Author: Haraldur Ólafsson
Co-Author Affiliation:
Abstract Title:
Large resuspension of volcanic ash at Eyjafjallajökull, due to a local orographic windstorm
Abstract:
Following the Eyjafjallajökull volcanic eruption, large quantities of ash was deposited in the vicinity of the volcano. A few times, this ash was resuspended into the air and carried long distances. An investigation of one of these cases that produced extremely high levels of ash in Reykjavík city reveals that the resuspension of ash was a consequence of small-scale acceleration of the wind field at the edge of the volcano, giving a new dimension of the concept of the upscaling effect of mountain-induced winds for atmospheric forecasting.

Session Number: P2p
Presenting Author: P.W. Chan
Author Email: pwchan@hko.gov.hk
Author Affiliation: Hong Kong Observatory
Co-Author: Y.F. Lee
Co-Author Affiliation: Hong Kong Observatory
Abstract Title:
Application of brightness temperature data from a ground-based microwave radiometer in the alerting of low-level windshear
Abstract:
The brightness temperature measurements from a ground-based microwave radiometer are primarily used for retrieving temperature and humidity profiles of the troposphere. However, in terrain-disrupted airflow, the temperature and/or humidity of the boundary layer of the atmosphere may fluctuate as a result of the corresponding changes in the wind. As such, the degree of fluctuations of the brightness temperatures, e.g. as represented by their standard deviations, may be useful in detecting and alerting the occurrence of low-level windshear to be encountered by the aircraft for terrain-induced windshear. This approach is studied in the present paper by considering the pilot windshear reports of the spring in two years at the Hong Kong International Airport (HKIA). Spring season is chosen because terrain-induced windshear is the major type of windshear at this time of the year at HKIA when the prevailing airflow is disrupted by the complex terrain around the airport in the stable boundary layer. It turns out that the standard deviations of the brightness temperatures for those oxygen microwave channels with effective ranges within the atmospheric boundary layer show skills in capturing the pilot windshear reports. On the other hand, the water vapour microwave channels do not show skills in detecting the windshear. It is suggested that, for terrain-induced windshear situation at HKIA, the low-level temperatures fluctuate coherently with the winds, but not so for the water vapour content as may be expected in Foehn wind situation.

Session Number: P2q
Presenting Author: P.W. Chan
Author Email: pwchan@hko.gov.hk
Author Affiliation: Hong Kong Observatory
Abstract Title:
An event of tail strike of an aircraft due to terrain-induced windshear at the Hong Kong International Airport
Abstract:
In the morning of 5 March 2010, an aircraft experienced tail strike when it departed from the south runway of the Hong Kong International Airport to the west. This paper documents the meteorological conditions in the tail strike event, and discusses the alerting and the forecasting aspects of the event. Based on the analysis of the aircraft manufacturer, the tail strike is believed to arise from significant windshear (headwind loss) experienced by the aircraft. By analyzing the surface and the LIDAR observations, it appears that the significant windshear is related to disruption of the background southwesterly flow by the complex terrain near the airport. From the surface observations, there is a microscale cyclone at the western part of the south runway. The radial velocity image of the LIDAR also depicts an area of reverse flow in that region against the background southerly flow. The alerting of the windshear based on the two windshear alerting algorithms developed by the Hong Kong Observatory is discussed, and it turns out that the anemometer-based windshear algorithm could successfully capture this windshear occurring close to the ground. On the other hand, due to geometrical constraint, the LIDAR does not pick up the headwind loss experienced by the aircraft. The forecasting of this windshear event is considered by performing high resolution (down to a horizontal resolution of 50 m) using a mesoscale numerical weather prediction model. The simulated headwind profile at the event time is generally consistent with the aircraft data, though the headwind loss in the simulation is smaller than the reality. Together with the forecast wind gusts, it may be possible to alert the aviation weather forecaster at an earlier time about the occurrence of terrain-induced windshear over the south runway in this particular event.

Session Number: P2r
Presenting Author: Irene Schicker
Author Email: irene.schicker@boku.ac.at
Author Affiliation: Institute of Meteorology, University of Natural Resources and Life Sciences
Co-Author: Delia Arnold, Petra Seibert
Co-Author Affiliation: Institute of Meteorology, University of Natural Resources and Life Sciences
Abstract Title:
Updating the currently available landuse data in WRF: impacts on simulations for the Austrian Inn Valley
Abstract:
Currently available landuse data in the WRF model, the so-called USGS landuse data, are based on the Global Land Cover Characteristics Data Base Version 2.0 compiled from AVHRR satellite data of April 1992 - March 1993 with a resolution of 1 km. A global standardised landuse data set is useful especially when simulating in remote regions but in many areas, especially in the Alps, one can find pixels with inappropriate landuse. In the USGS landuse data Alpine glaciers are surrounded by the class “wooded tundra” whereas the class “barely vegetated” would be more suitable. In addition, landuse may change significantly even within a few years.
In Europe there have been efforts to generate a European landuse data base since the early 1990ies. Meanwhile, three different versions of the CORINE landuse data, consisting of 44 different classes, are available: CLC1990, CLC2000, and CLC2006 (not completely finished yet). These data are available for two different horizontal resolutions, 100 m and 250 m.
Following Pineda et al. (2004), the CLC2000 and CLC2006 have been remapped on the 24 USGS categories. This allows, on one hand to be able evaluate changes of using better resolved data, and, on the other, it allows us using the default surface parameters such as roughness length or albedo which at the moment are not available for the 44 CORINE landuse classes. It needs to be pointed out too, that for some European countries like Switzerland (CLC2000) or Greece (CLC2006) no landuse
data are available at the moment. Therefore, in areas of missing CORINE data the USSG data was taken.
For the innermost 0.8 km grid size modeling domain used in this study, covering the Austrian part of the Inn Valley, 74 % of the grid points differ between USGS landuse data and the remapped CLC2000.
To evaluate the effects of using different sets of landuse data on the meteorological simulations a comparison between old and new landuse data for a summer case in the
Austrian Inn Valley and surroundings will be shown.
In addition, we believe that some of the parameters used in the LSM part of the WRF model, erg. roughness length and albedo, should be revised and changed accordingly if needed.
Pineda, N., Jorba, O., Jorge, J., Baldasano, J.M. (2004). Using NOAA-AVHRR and SPOT-VGT data to estimate surface parameters: application to a mesoscale meteorological model. Int. J. Remote Sens., 25, 129-143.

Session Number: P2s
Presenting Author: Alan Gadian
Author Email: alan@env.leeds.ac.uk
Author Affiliation: National Centre for Atmospheric Science, UK
Co-Author: Sarah-Jane Lock, Stephen Mobbs
Co-Author Affiliation: National Centre for Atmospheric Science, UK
Abstract Title:
Demonstration of a cut-cell representation of orography for modelling atmospheric flow over 3D very steep hills
Abstract:
Advances in computing are enabling atmospheric models to operate at increasingly high-resolution, giving rise to more variations in the underlying orography Consequently, high-resolution models must overcome instabilities associated with terrain-following approaches. This work further explores the capabilities of being captured by the model grid. Comparison with a benchmark orographic test case demonstrates good results. Further tests show the potential for the cut-cell approach for a 3D case and for stably resolving flows over very steep orography.

Session Number: P3a
Presenting Author: Željko Večenaj
Author Email: zvecenaj@gfz.hr
Author Affiliation: Faculty of Science, Department of Geophysics, University of Zagreb, Zagreb Horvatovac 95, Croatia
Co-Author: Danijel Belušić, Branko Grisogono
Co-Author Affiliation: Univ. of Zagreb, Faculty of Science, Department of Geophysics, Zagreb Horvatovac 95, Croatia
Abstract Title:
On the turbulence integral length scale at the NE Adriatic coast
Abstract:
During past few decades, a number of international campaigns (e.g. MAP 1999) and local field experiments (e.g. measurements in the town of Senj and Vratinik Pass) were conducted at the north-eastern (NE) Adriatic coast, within which high frequency measurements of wind were performed. While measurements during MAP were strictly focused on the certain bora events, instruments in Senj and Vratnik Pass were continuously operative for more than two years and almost a year, respectively, recording all kinds of airflows. Using these data sets, we have a great opportunity to investigate turbulence characteristics of the local winds in this region.
In this study we deploy two kinds of measurements. The first kind is single point horizontal and vertical wind measurements at Senj (44.99°N, 14.90°E, 2 m above MSL, 13 m above the ground, March 2004 – June 2006) and Vratnik Pass (44.98°N, 14.98°E, 600 m above MSL, 10 m above the ground, Oct. 2004 – Sep. 2005) with the WindMaster ultrasonic anemometers (Gill Instruments). They recorded the data with a sampling frequency of 4 Hz. The second kind are MAP IOP 15 (07 Nov. 1999) aircraft measurements (NCAR Electra), taken offshore, above the Adriatic Sea (370 and 680 m above MSL), perpendicular to the actual bora wind. The sampling frequency of the 3D wind speed was 25 Hz, which, with a mean aircraft wind speed of 100 m s-1, gives the data spatial resolution of ≈ 4m.
We estimated turbulent kinetic energy, its dissipation rate and integral turbulence length scale (Λ) for bora events using all three data sets, and for the events of wind which has the opposite direction of bora, but only for Vratnik Pass data. We have noticed atypical behavior of Λ with the mean wind speed which shares some similarities and differences with respect to different locations and type of the data used, as well as the wind direction. The question that arises is what is the cause of this behavior?

Session Number: P3b
Presenting Author: Željko Večenaj
Author Email: zvecenaj@gfz.hr
Author Affiliation: Faculty of Science, Department of Geophysics, University of Zagreb, Zagreb Horvatovac 95, Croatia
Co-Author: Vjeran Mađarević, Kristian Horvath, Branko Grisogono
Co-Author Affiliation: Unive. of Zagreb, Faculty of Science, Department of Geophysics, Zagreb Horvatovac 95, Croatia; Met. and Hyd. Service, Zagreb Grič 3, Croatia
Abstract Title:
Turbulence averaging interval for summer bora flows at the middle of the NE Adriatic coast
Abstract:
At the Eastern Adriatic coast often blows a downslope windstorm called bora. It flows from the north-eastern (NE) quadrant, and it occurs most frequently during winter seasons. Bora mean wind speed can surpass 20 m s-1 and due to its gustiness it reaches speeds greater than 60 m s-1. During such events, the turbulence is strongly developed in the lee of the mountains; moreover, sub-mesocale and turbulent structures are additionally complicated at the middle of the NE Adriatic coast due to the surrounding mountains.
Bora is investigated at the NE Adriatic coast more intensively and systematically than at the middle-eastern, not to mention the southern Adriatic part, mainly because it occurs more often at the NE Adriatic and is stronger there. Nevertheless, severe bora at the middle-eastern and southern Adriatic coast is not a rarity at all. Partially inspired by this fact, we have installed three levels of horizontal and vertical wind and sonic temperature sensors at the middle-eastern Adriatic coast: on the hill of Pometeno Brdo (43.62°N, 16.47°E, 600 m above MSL), inland from the city of Split, at heights of 10, 20 and 40 m above the ground. Measurements are performed with WindMaster ultrasonic anemometers (Gill Instruments) with a sampling frequency of 5 Hz.
In order to investigate turbulence, a suitable time/space averaging interval has to be used in order to define turbulent perturbations; these quantities later on define turbulent kinetic energy, gustiness, etc. This study addresses the turbulence averaging interval for bora events on the hill of Pometeno Brdo (”Swept-Away Hill”) during three months of the last summer. The instruments remain there over a whole year. There are indications that the appropriate averaging interval for bora turbulence at the more studied NE Adriatic coast is not the same as that for the middle-eastern Adriatic coast studied here.

Session Number: P3c
Presenting Author: Sébastien Blein
Author Email: sebastien.blein@hmg.inpg.fr
Author Affiliation: LEGI, Laboratoire des Écoulements Géophysiques et industriels, (Grenoble France)
Co-Author: Christophe Brun
Co-Author Affiliation: LEGI
Abstract Title:
Atmospheric turbulence high resolution in mountain region
Abstract:
The Atmospheric Boundary Layer (ABL) in mountain region is still a complex topic from the point of view of turbulent flows numerical simulation and modeling. There is no model able to describe accurately the boundary layer at the ground surface in the sense of fluid mechanics e.g. less than the first meter in the vertical direction. In the present study, the MesoNH model (Météo France and Laboratoire d\'Aerologie, Toulouse) is used down to the two first meters above the ground in a complex topography. A real mountain slope overlooking Grenoble in the Alps is reproduced in the simulation. Idris french calculators (IBM SP6 512 nodes) are used to run a grid of about 10 million points, 2 meters vertical and 10 meters horizontal at the lowest atmospheric layer. A realistic meteorological situation is selected from a panel of stable stratified events to initialize the calculation. From the meteorological condition of the winter day selected (thanks to ECMWF archives), the calculation is governed by the diurnal cycle from midday (12h00 L.T.) to after the sunset (19h00 L.T.). The establishing of a wall jet (few tens of meters thick and 1 m/s of maximum speed) descending slopes is observed when radiative cooling at the ground is sufficient. Even if stable stratified atmospheric condition is present, strong turbulence could be observed in the vicinity of the ground surface when radiative cooling is present. Katabatic flows could create turbulent structures and contribute to scalar transport and mixing. Although results have shown interesting behavior of the ABL, it is shown that finer description or specific surface boundary layer model is necessary to get better results.

Session Number: P3d
Presenting Author: Branko Grisogono
Author Email: all4omis@gmail.com
Author Affiliation: Department of Geophysics, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia
Co-Author: Josipa MILOVAC, Maja T. PRTENJAK, Tomislav BAŠIĆ
Co-Author Affiliation:
Abstract Title:
An airflow over the Dinaric Alps simulated with a modified mixing-length formulation in WRF model
Abstract:
Numerical meteorological forecasting models still do not possess a sufficient accuracy to perform hour-to-hour and site-to-site reliable weather prognosis, say, within a standard deviation of a forecasted and later on possibly observed parameter at a given site. One of the reasons that the models miss certain parts of airflow evolution is in inadequate model parameterizations of subgrid scale processes, such as mixing due to turbulence. This parameterization issue is even more present in cases of coastal mountain stratified airflows where various air masses interact over different underlying complex surfaces. A generalized so-called ‘z-less‘‘ mixing length-scale is deployed in WRF simulating the airflow over the western Croatia and the NE Adriatic coast for a few days of late June 2008. This length-scale is uniformly valid for stably-stratified airflows while taking an explicit care of existing local turbulence, mean wind-shear, buoyancy and turbulent Prandtl number; i.e., the length-scale formulation is valid and monotonic for all positive gradient Richardson numbers, Ri, Ri ≥ 0 while also including local values of Prandtl number. The related simulation is compared to its counterpart using a standard WRF parameterization suite and to the regular near-surface and air-sounding data observed in the area. The airflow studied pertains to a moderate bora flow that is locally and occasionally interrupted or overtaken by diurnal circulations.The preliminary results show that the simulation with the new generalized mixing length-scale provides a wider range of variability for the important meteorological variables, such as the near-surface wind direction and better agremeement with the importanat observed data, such as the near-surface wind speed. Almost needless to say, sufficient spatio-temporal variability of the modeled fields has been often missing in outputs from majority of numerical meteorological models. Hence, this case study contributes to modeling sub-mesoscale details of airflow over complex terrain.

Session Number: P3e
Presenting Author: Lorenzo Giovannini
Author Email: Lorenzo.Giovannini@ing.unitn.it
Author Affiliation: Atmospheric Physics Group, Department of Civil and Environmental Engineering, University of Trento. Via Mesiano 77, 38123 Trento, Italy.
Co-Author: Dino Zardi (1), Elena Bee (1), Massimiliano de Franceschi (2), Lavinia Laiti (1), Roberto Santin (1), Stefano Serafin (3)
Co-Author Affiliation: (1) Atmospheric Physics Group, Department of Civil and Environmental Engineering, University of Trento, (2) Major Seminary, Dioecese of Bolzano-Bressanone, Italy; (3) Institute of Meteorology and Geophysics, University of Vienna
Abstract Title:
Characterization of daily-periodic valley winds in the valleys around Trento
Abstract:
The city of Trento lies in the Adige Valley in the Alps, at a point where various narrow tributary valleys or gullies join the valley, among which in particular the Lakes Valley, ending in the Adige Valley north-west of Trento through an elevated saddle. Daily-periodic winds, regularly occurring in the above valleys, are investigated on the basis of a dataset from surface stations.
The dataset covers the period 2004-2009 and includes data of radiation, pressure, air temperature and relative humidity, as well as wind speed and direction.
A suitable subset of clear-sky days, free from synoptic scale upper winds, are selected on the basis of radiation data and of a preliminary inspection of daily wind cycles. Monthly mean values of daily cycles of air temperature, pressure, wind speed and direction allow an overview of the development of an organised circulation along the valley under clear sky fair weather conditions. Along-valley pressure gradients are clearly detected along with their diurnal reversal driving the valley winds. Wind roses and hodographs show how local topography close to the station may strongly affect the local features of the wind. The confluence of the two main streams north of Trento is also explored.

Session Number: P3f
Presenting Author: Stefano Serafin
Author Email: stefano.serafin@univie.ac.at
Author Affiliation: University of Vienna, Department of Meteorology and Geophysics
Co-Author: Dino ZARDI
Co-Author Affiliation: University of Trento, Department of Civil and Environmental Engineering, Atmospheric Physics Group
Abstract Title:
Daytime heat transfer processes related to slope flows and turbulent convection in an idealized mountain valley
Abstract:
The mechanisms governing the daytime development of thermally driven circulations in idealized two-dimensional valleys are investigated by means of large eddy simulations. In particular, the impact of slope winds and turbulent convection on the heat transfer from the vicinity of the ground surface to the core of the valley atmosphere is examined.
Subsidence in the valley core, arising to compensate the upward mass flux related to upslope flows, generates a top-down warming mechanism, as opposed to the bottom-up warming resulting from turbulent convection at the valley floor. Advective top-down warming and convective bottom-up warming are shown to antagonize each other, the former prevailing in the morning and the latter in the afternoon.
An evaluation of the depth of the atmospheric layer affected by the slope wind system is also provided. The free atmosphere descent mechanism first described by Whiteman and McKee (1982) appears to be limited to the depth below the level of neutral buoyancy of air parcels in the thermal plumes devoloping on mountain tops.
Due to the occurrence of slope circulations, the boundary layer appears to have peculiar features in mountainous regions: the mountain boundary layer (MBL) may include a CBL, but is not limited to it. Elevated layers, where the atmosphere is warmed and becomes weakly turbulent due to advection of heat and TKE, are also included in it. A non-turbulent stable region where air subsides towards the valley floor to compensate upward motion along the slopes is also embedded in the MBL, at least in the early stages of its development. As the daily heating cycle progresses, the CBL and elevated stable layers may merge into a unique mixed layer. These features are consistent with previous findings from airborne measurements.

Session Number: P3g
Presenting Author: Rosey Grant
Author Email: r.grant@see.leeds.ac.uk
Author Affiliation: Institute for Climate and Atmospheric Science, University of Leeds
Co-Author: Barry Gardiner, Stephen Mobbs, Andrew Ross
Co-Author Affiliation: Forest Research, Northern Research Station, Forestry Commission; Institute for Climate and Atmospheric Science, University of Leeds; National Centre for Atmospheric Science, University of Leeds
Abstract Title:
An observational dataset of canopy air flows over complex terrain
Abstract:
The investigation of forest air flows over complex terrain has been, until recently, limited to a handful of modelling and laboratory studies yet the ability to understand, model and predict canopy flows over complex terrain will benefit many applications; improving the prediction of the yield of wind turbines, understanding the exchange of carbon dioxide with the atmosphere, minimizing wind damage to managed forests and improving the skill of numerical weather prediction models. It has been noted that progress on this subject has been limited by a lack of field measurements to validate recent model developments. A unique observational dataset of air flow measurements from within and above a forest situated on a ridge is presented.
Vertical velocity profiles within and just above the canopy were measured on the windward slope, the summit and the lee slope of the ridge. The summit profile resembled that of a profile within and above a canopy on flat terrain with little variation in wind speed below the canopy and an inflection point at the canopy top. On the windward slope significant amounts of –(u\'w\') ̅ at the canopy top indicated that turbulent mixing was acting strongly to transport higher momentum air down into the canopy. The velocity profile on the lee slope depended on the size of a separation region that, under certain conditions, was found to develop.
The direction of the mean wind within the canopy on the lee slope is the dependent on the hill-induced pressure gradient (which tends to drive a reversed flow up the lee slope), and on turbulent mixing (which tends to drive the flow down-slope through the mixing of higher momentum air from above the canopy). If the hill slope is sufficiently large or the canopy sufficiently deep then flow separation can occur. A region of flow separation was observed to extend beyond the top of the canopy. Within the separation region, there was little variation in wind speed or momentum flux with height.
Preliminary comparisons between observed case studies and model simulations are presented. The model is found to successfully capture the main features of these flows. Areas where the model was less successful are attributed to the inhomogeneous nature of the canopy and the terrain at the field site, and to the low resolution of the model.

Session Number: P3h
Presenting Author: Temple R. Lee
Author Email: trl2y@virginia.edu
Author Affiliation: University of Virginia
Co-Author: Stephan F. J. De Wekker
Co-Author Affiliation: University of Virginia
Abstract Title:
Carbon dioxide variability and frontal passages at a forested mountaintop in the Blue Ridge Mountains
Abstract:
Continental mountaintop locations are increasingly being used for CO2 monitoring, and investigations are needed to better understand measurements made at these locations. In this presentation, we discuss CO2 variability at Pinnacles (38° 37’ N, 78°21’W), a new mountaintop site in the central Appalachian Mountains 1017 m above mean sea level, and contrast the diurnal and subdiurnal variability on days with cold front passages with clear, fair weather days. We also explore the use of CO2 variations to better determine the timing of frontal passages in mountainous terrain. This determination is often difficult from meteorological data alone because terrain-induced frontal deformation obfuscates the frontal zone.
Variability in CO2 mixing ratios at Pinnacles is largest during cold front passages outside the growing season and on clear, fair weather days during the growing season. 67% (60%) of the frontal passages during the non-growing (growing) season have larger mean postfrontal CO2 mixing ratios. We observe a short-lived increase in CO2 mixing ratio during eastward-moving cold fronts due to the accumulation of trace gases along frontal boundaries. CO2 mixing ratios do not return to their prefrontal levels until 1-2 days following southward-moving cold fronts, which is consistent with the postfrontal advection of air from the Northeastern United States and corroborated with in situ carbon monoxide observations.
We find that CO2 mixing ratio shows more consistent variations during fronts than other trace gases. We therefore conclude that changes in CO2 mixing ratio during cold fronts can be used to determine accurately the timing of frontal passages in complex terrain.

Session Number: P3i
Presenting Author: N.Vijaya Saradhi
Author Email: nvijaysaradhi@yahoo.com
Author Affiliation: Department of Meteorology & Oceanography, Andhra University
Co-Author: S.S.V.S.Ramakrishna
Co-Author Affiliation: Department of Meteorology & Oceanography Andhra University
Abstract Title:
Numerical Simulation of Mala cyclone with different boundary layer schemes
Abstract:
Tropical cyclones are magnificent atmospheric vortices that inhabit the tropical region. In recent years North Indian Ocean cyclones are increasing and also becoming more intense. This seems to be due to climate change. Several attempts to associate tropical cyclone trends with climate change resulting from many factors that have led to concentrate on tropical cyclone prediction (Emanuel 1987; Evans 1992; Lighthill et al. 1994). In the present study we made an attempt to simulate a category 4, Mala cyclone in all its various phases of its life cycle giving emphasis to the Dynamics of cyclone development over this region. In this study emphasis has been given to delineate the planetary boundary layer (PBL) processes using different PBL schemes such as Blackadar, Burk-Thompson, Eta Mellor-Yamada, MRF and Gayno-Seaman. The MM5 model is modified to have a two way nested domain of 90 km and 30 km resolution in the Horizontal.
From the results of the simulation, it is found that the Maximum intensity is reproduced with the ETA Mellor-Yamada PBL scheme at 1800 UTC of 26 April 2006 in terms of minimum Sea level pressure of 946 hPa at the mature stage with 30 km horizontal resolution. At this stage the India Meteorological Department (IMD) reported a minimum sea level pressure of 922 hPa observed at 1200 UTC of 28 April 2006 with 90km resolution. The simulated maximum precipitation is noted in the Southeastern quadrant of the cyclone with a maximum precipitation of 45 cm/day occurred on 28 April 2006 and 29 April 2006 before crossing the Arabian coast. This agrees very well with the Tropical Rainfall Measuring Mission (TRMM) satellite estimate of 45 cm/day on 29 April 2006. The estimated rainfall with 30 km resolution was higher compared to the TRMM resolution. The experiment shows that the model predicted movement of the cyclone with the MRF Mellor-Yamada PBL scheme compared well with the IMD track at the landfall position but the tracks derived with the other PBL schemes deviated from observed track. The Blackadar, ETA Mellor-Yamada PBL schemes simulated the intensification well with 30 km horizontal resolution although it overestimated the rainfall rates as mentioned earlier. Thus NCAR/MM5 is able to simulate the essential features associated with the evolution of the Mala cyclone that struck the Myanmar coast on 29 April 2006 at 1800 hrs.

Session Number: P3j
Presenting Author: Dino Zardi
Author Email: Dino.Zardi@ing.unitn.it
Author Affiliation: Atmospheric Physics Group, Department of Civil and Environmental Engineering, University of Trento
Co-Author: Richard Rotunno
Co-Author Affiliation: National Center for Atmospheric Research, Boulder, CO, USA
Abstract Title:
A simple model for the convective boundary layer development in a mountain valley
Abstract:
A simplified model of CBL growth is proposed, extending previously introduced concepts, to cover processes specifically occurring in mountain valleys. Assuming a simple trapezoidal valley cross-section, a first order mixed layer scheme is adopted to reproduce the thermal structure of the atmosphere above the valley floor. The up-slope mass and heat flux produced by sidewall heating is estimated by means of the Schumann (1990) extension of the classic Prandtl (1942) model. The effect of subsidence warming, implied by the upslope flow, is evaluated by estimating the compensating downward motion from mass conservation and assuming a linearly stratified free atmosphere. By combining all the governing equations and related constraints, arising from continuity and consistency conditions, an evolution equation for the mixed layer height is obtained, which incorporates all the effects and the physical and geometrical parameters cooperating in the control of the diurnal evolution of the layer. As a result, the model allows one to evaluate how the air in the valley mixed-layer warms with respect to the air over an adjacent plain (where the warming is estimated by a classical CBL model) and how the various factors interact to determine this enhanced heating. Results from a large-eddy simulation (LES) of the daily evolution of the CBL in a similar idealised valley are shown to compare reasonably well with the predictions of the present simplified model.

Session Number: P3k
Presenting Author: Hálfdán Ágústsson
Author Email: halfdana@hi.is
Author Affiliation: University of Iceland, Icelandic Meteorological Office and Institute for Meteorological Research
Co-Author: Haraldur Ólafsson
Co-Author Affiliation:
Abstract Title:
Katabatic winds and land breeze
Abstract:
During the summer, winds in Iceland and Norway often blow downslope and towards the sea during nighttime. These winds are sometimes referred to as land breeze and sometimes as katabatic winds. Idealized simulations reveal that the winds are almost of pure katabatic nature and that there is hardly any land breeze. In the winter, there is however both land breeze and katabatic flow. Steep mountains close to the coast hamper the land breeze, while winds generated by gently sloping topography further away from the coast add to the land breeze.

Session Number: P3l
Presenting Author: Susan Lee
Author Email: s.e.lee@leeds.ac.uk
Author Affiliation: National Centre for Atmospheric Science, University of Leeds, Leeds LS2 9JT, United Kingdom
Co-Author: Ralph Burton, Stephen Mobbs, Mark Bart, James Groves and Dan Walker
Co-Author Affiliation: University of Leeds
Abstract Title:
Applying the WRF model at a regional scale to quantify orographic effects on two bio-crop sites in Yorkshire
Abstract:
The Microclimates Consortium consists of four research groups from the universities of Leeds, Lancaster, Glasgow and Stirling as well as Rothampstead Research. This consortium is developing new downscaling methodology to apply to three diverse demonstration applications (micro-climate prediction, wind farm impacts on peatland carbon balance and the application of the micro-climate model to biorenewables) in the land-based renewables field.
The WRF (Weather Research and Forecasting) model was used to simulate the local meteorological conditions at two sites (having differing orography) in Yorkshire, where AWS instruments have also been installed. Two approaches were used. In the first simulation, a 3-day high-resolution run was performed. This simulation used three nested domains with 5, 1, and 0.2 km horizontal grid resolutions, with the inner domain covering a region of approximately 48 x 48 km and centred over Leeds. In the second simulation, a larger-scale, month-long simulation was performed, with nested domains at 36, 12 and 4km resolution, and the inner domain covering the north of England and south of Scotland. NCEP GFS 0.5 degree analyses were used to initialize both simulations. The representation of the underlying orography is, of course, somewhat smoothed in the lower-resolution run.
Meteorological data for December 2010 and January 2011 were extracted for the two AWS sites. These data are compared with the model results from the two different types of simulation, and the effect of orography upon several parameters (such as surface wind speed and temperature) is assessed.

Session Number: P3m
Presenting Author: Olivier Caumont
Author Email: olivier.caumont@meteo.fr
Author Affiliation: CNRM-GAME (Météo-France, CNRS), Toulouse, France
Co-Author: Claude Cayol (1), Béatrice Fradon (2)
Co-Author Affiliation: (1) Central France Interregional Division (Météo-France), Paris, France, (2) Weather Radar Centre (Météo-France), Toulouse, France
Abstract Title:
Initialization of a non-hydrostatic high-resolution model with weather radar dual-polarization data for deep convection forecasting in a mountainous area
Abstract:
Since a few years, some national weather services have begun (or planned) to upgrade their weather radar networks to dual-polarization capabilities. For instance, France is now equipped with 10 polarimetric radars (out of 24) and the whole network will be upgraded in the near future. This choice is primarily motivated by the need to improve the overall quality of existing radar products such as quantitative precipitation estimation.
Besides their role in data quality controls, dual-polarization observations also provide additional information with respect to conventional reflectivity about hydrometeors, such as size, shape, etc. It is thus of great interest to use these data to initialize high-resolution atmospheric models in order to improve their initial states and subsequent forecasts.
In this study, the operational limited-area French model Arome is used to investigate the potential benefit of the assimilation of polarimetric observations. The Arome assimilation system is of three-dimensional variational (3DVar) type, with a typical refresh cycle of 3 hours. Though hydrometeor contents are predicted by the forecast model, they have not been included in its assimilation system control variable, and they are currently simply passed on from the background state to the analysis without being altered.
In the last decades, a significant effort has been put on the use of dual-polarization measurements to identify hydrometeors, and current research also addresses the derivation of quantitative information, e.g., hydrometeor contents, from these measurements. All this work paves the way for a direct assimilation of hydrometeor contents retrievals. This is done in this study in a simple way: hydrometeor contents are directly modified after the 3DVar analysis step according to polarimetric observations, and the resulting model state is used as initial conditions for the following forecast. This technique will be illustrated for deep convection occurring in a mountainous area located in southeastern France.

Session Number: P3n
Presenting Author: Simon Vosper
Author Email: simon.vosper@metoffice.gov.uk
Author Affiliation: Met Office, UK
Co-Author: Helen Wells, Mark Weeks, Stuart Webster
Co-Author Affiliation: Met Office, UK
Abstract Title:
Assessment of orographic drag parametrization schemes in simulations of flow across the Antarctic Peninsula
Abstract:
Orographic drag parametrization schemes are a necessary component of weather forecast and climate models. The representation of drag due to flows over unresolved (sub-grid-scale) orography in numerical models is required in order for them to correctly represent the large-scale atmospheric circulation. Typically, the parametrization schemes are tuned in order to improve the
representation of synoptic-scale weather patterns, without considering their impacts on the mesoscale. For example, the representation of drag
due to the flow-blocking effects of sub-grid mountains may improve the performance of a model globally, but this may be at the expense of the more local aspects of the modelled flow, immediately downwind of a mountain range.
A series of numerical simulations of flow across the Antarctic Peninsula have been conducted using the Met Office Unified Model. Cases of cross-barrier flow were selected from the recent Orographic Flow and the Climate of the Antarctic Peninsula (OFCAP) field campaign and simulations performed at a range of resolutions in order to assess the impact of drag parametrization schemes on the local flow. It is shown how simulations such as these can be used to evaluate the performance of drag parametrization schemes and determine the extent to which they correctly represent the decelerating effect of the sub-grid orography.

Session Number: P3o
Presenting Author: Marius Opsanger Jonassen
Author Email: Marius.Jonassen@gfi.uib.no
Author Affiliation: Geophysical Institute, University of Bergen Allegaten 70 5007 Bergen
Co-Author: Hálfdán Ágústsson, Haraldur Ólafsson, Joachim Reuder, Ólafur Rögnvaldsson & Dubravka Rasol
Co-Author Affiliation:
Abstract Title:
Assimilating data from an unmanned aircraft to improve a forecast of orographic winds
Abstract:
Numerical simulations with the WRF atmospheric model have been improved by assimilating data obtained with the Unmanned Aerial System (UAS), SUMO. The UASs are at the forefront of present day instrumental platform technology and provide with their unique coverage in both space and time a highly flexible tool for the described purpose. The method is demonstrated for two cases of terrain induced meso-scale flow in the summer of 2009 during the MOSO field campaign in Iceland. The first case is a sea-breeze event that took place at the southwest coast of Iceland and the second is a light gravity wave induced downslope windstorm that was observed in the lee of Mount Esja.

Session Number: P3p
Presenting Author: Jan Kysely
Author Email: kysely@ufa.cas.cz
Author Affiliation: Institute of Atmospheric Physics, Prague, Czech Republic
Co-Author: Ladislav Gaal, Romana Beranova
Co-Author Affiliation: Institute of Atmospheric Physics, Prague, Czech Republic
Abstract Title:
Climate change scenarios of heavy precipitation events in mountainous regions of Europe
Abstract:
Heavy precipitation events are associated with large negative impacts on human society, mainly as they may trigger floods and landslides. There is also concern that climate change may increase severity of precipitation extremes in many parts of Europe, even in areas and seasons in which mean precipitation is projected to decline. Mountainous regions and areas with complex orography are particularly prone to heavy precipitation and floods, and uncertainty in possible changes associated with climate change may be enhanced due to complexity of interactions between orography, atmospheric circulation, and local processes.
The study examines possible changes in high quantiles of precipitation amounts in scenarios of the late 21st century climate (2070-2099) against the recent climate in an ensemble of regional climate model (RCM) simulations over Europe from the EU-FP6 ENSEMBLES project. The RCMs have a resolution around 25 km and are driven by several global climate models. The projected changes are evaluated in winter and summer seasons, and on a wide range of time scales from hourly to multi-day amounts. The region-of-influence method is applied as a pooling scheme when estimating distributions of seasonal maxima of precipitation, which leads to spatial patterns of high quantiles that are smoothed compared to local analysis.
We focus on a comparison of results (scenarios) for selected mountainous and lowland regions of Europe, and evaluate altitudinal dependence of the projected changes of heavy precipitation and their possible links to changes in atmospheric circulation. Specific attention is paid to the performance of the pooling scheme, particularly how the regional homogeneity criterion is met in areas with complex topography. Uncertainty of the projected changes due to inter-model variability is also assessed and compared for selected regions.

Session Number: P3q
Presenting Author: Vanda Grubišić
Author Email: vanda.grubisic@univie.ac.at
Author Affiliation: University of Vienna, Austria, Department of Meteorology and Geophysics
Co-Author: Rita Nogherotto; Roy Rasmussen et al.
Co-Author Affiliation: University of Vienna, Austria; NCAR, Boulder, CO, USA
Abstract Title: Drying Ratio of the Colorado Mountains under Climate Change Conditions
Abstract:
Results of high-resolution simulations of seasonal snowfall over the Colorado Headwaters region (Rasmussen et al. 2010) under the current and future warmed climate conditions show that global warming is expected to accelerate the hydrological cycle, increasing the precipitation over the Colorado Headwaters region by 10-25%, with the enhancement being less in the high-elevation parts of the region. Global models predict a 4-7% increase over the same region. It is therefore critical to examine climate change impacts in this region using higher resolution models in order to more realistically simulate orographic precipitation and evaporation processes.
In this study we examine the efficiency of mountains in the Colorado Headwaters region in producing orographic precipitation. Drying ratio, defined as the ratio of total precipitation to the incoming water vapor flux, is used as the measure of efficiency. As an integral quantity, the water vapor flux reflects the effects of both the water vapor availability and the vertical profile of the horizontal wind. The sensitivity of the drying ratio to the model horizontal resolution (2-36 km) is explored with a series of current climate simulations; its sensitivity to climate change is explored under a future warmed climate scenario. The analysis is based on high-resolution climate-runoff WRF simulations for the Colorado Headwaters region for the current and future warmed climate for four water years, one dry (2001/2002), two average (2003/2004 and 2005/2006) and one wet year (2007/2008), exploiting the Pseudo-Global-Warming (PGW) approach for the future climate simulations.

Session Number: P3r
Presenting Author: Željko Večenaj
Author Email: zvecenaj@gfz.h
Author Affiliation: Department of Geophysics Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia
Co-Author: Danijel Belušić, Branko Grisogono
Co-Author Affiliation: Univ. of Zagreb, Department of Geophysics, Faculty of Science, 10000 Zagreb, Croatia
Abstract Title:
Climatology of the Adriatic winds in the town of Senj and Vratnik Pass
Abstract:
The eastern Adriatic coast is famous for the occurrence of strong winds, mostly bora and sirocco, which, due to the frequent severity, represent a great threat to traffic, infrastructure, tourism and agriculture, as well as great potential in wind energy resources. Therefore, there is a great and continuous interest in the meteorological community for airflow studies in this region.
This study is focused on the data collected in the town of Senj and Vratnik Pass at the north-eastern Adriatic coast. Senj is settled literally at the coast (44.99°N, 14.90°E) while Vratnik Pass (44.98°N, 14.98°E) is ~ 10 km east of Senj in the lee of Dinaric Alps, 600 m ASL. Single point measurements of horizontal and vertical wind sampled at 4 Hz with the WindMaster ultrasonic anemometers (Gill Instruments) were performed 13 m and 10 m above the ground in Senj and Vratnik Pass, respectively. The anemometer in Senj was operative from March 2004 to June 2006, and the one in Vratnik Pass from Oct. 2004 to Sept. 2005.
We analyzed the data-sets in the period when both anemometers were operational. Due to various technical difficulties, this pertains to almost a nine month period between Oct. 2004 and Sept. 2005. For this period, we calculate and compare 1-h mean horizontal winds on both sites, classified with respect to the mean horizontal wind speed and mean direction. The most prominent features observed from this comparison are:
a) In ≈ 90 % of cases, strong bora in Vratnik Pass implies strong bora in Senj.
b) In ≈ 50 % of cases, strong SW wind in Vratnik Pass implies moderate sirocco in Senj.
c) In ≈ 50 % of cases, weak bora in Vratnik Pass implies weak sirocco in Senj.
A future work includes a quest on dynamical background of these features.

Session Number: P3s
Presenting Author: Guðrún Nína Petersen
Author Email: gnp@vedur.is
Author Affiliation: Icelandic Meteorological Office, Reykjavik, Iceland
Co-Author: Halldór Björnsson (1), Kristján Jónasson (2), Teitur Birgisson (2), Jón Blöndal (2), Nikolai Nawri (1,2)
Co-Author Affiliation: (1) Icelandic Meteorological Office, Reykjavik, Iceland, (2) Department of Computer Sciences, University of Iceland, Reykjavik, Iceland
Abstract Title:
Preliminary study of the wind resource in Iceland
Abstract:
Iceland has considerable renewable energy resources. While hydro power and geothermal power have been exploited on a significant scale, less attention has been paid to wind power.
In preparation for the Nordic ICEWIND project, this study aims to build up a quality controlled data base of wind observations, and make a preliminary map of the wind resource. The data used come from 160 automatic weather stations distributed around Iceland, and consists of wind measurements every ten minutes. The operational period for the stations varies from 4 to 12 years, and in total there were 55 million observations to quality check (QC). In 81 stations more than 99% of the data passed QC, and in 131 stations more than 90% of the data passed QC. Most problems occurred during winter, especially in harsh climate mountain stations. The wind speeds were calculated up to 90m using a standard power law profile. The resulting data was then averaged for a cold season (Sep‐Apr) and warm season(May – Aug) and mapped. Furthermore, an idealized production curve for wind turbines was used to estimate the proportion of maximum production capacity for each season at each station. These results were then interpolated to a map which will aid in site selection.
Although the data base has been completed, the analysis of of the data and production of a wind atlas is ongoing. The inclusion of topographic effects, wind profile measurements and more detailed power production modelling will be further studied within the ICEWIND project, as well as the incorporation of wind from a reanalysis downscaled with a numerical weather prediction model (NWP) and using the RISOE Wind Atlas Analysis and Application Program (WASP) where applicable.

Session Number: P3t
Presenting Author: Marius Opsanger Jonassen
Author Email: Marius.Jonassen@gfi.uib.no
Author Affiliation: Geophysical Institute, University of Bergen Allegaten 70 5007 Bergen
Co-Author: Haraldur Ólafsson, Joachim Reuder and Jan Asle Olseth
Co-Author Affiliation:
Abstract Title:
Spatial variability of winds at the mountainous west coast of Norway
Abstract:
Multi-scale variability of winds in the complex terrain of Southwestern Norway is investigated using 20 years of observations from 9 automatic weather stations and reanalysis data. Significant differences between the large- and local-scale winds are found. These differences are mainly governed by the topography of Southern Norway. Winds from the northwest and southeast are found to be significantly reduced at the ground level due to larger-scale blocking and wake effects. Southwesterly and northeasterly winds are found to be orographically enhanced. At a local scale, there are differences in the wind speed distributions among the surface stations, both in space and time. It is shown that these differences can to a large extent be quantified in terms of the Weibull distribution function and associated with the respective geographical locations as discretized in four characteristic surface categories; offshore, inland, coast and mountain. The inland category is found to be associated with relatively low, but variable wind speeds whereas the coastal and offshore locations are dominated by more steady and stronger winds. The mountain wind speed distribution is fundamentally different from the others, it shares the variability of the inland locations but the higher average wind speed with the other categories.

Session Number: P3u
Presenting Author: Fiorella Acquaotta
Author Email: fiorella.acquaotta@unito.it
Author Affiliation: Dipartimento di Scienze della Terra, Università degli Studi di Torino, Via Valperga Caluso – 10125, Torino, Italia
Co-Author: Simona Fratianni
Co-Author Affiliation: Dipartimento di Scienze della Terra Università degli Studi di Torino Via Valperga Caluso – 10125, Torino, Italia
Abstract Title:
Temperature and precipitation in Bra. 149 years of meteorological observations (1862-2009)
Abstract:
Measurements of climatic parameters registered over periods longer than a century constitute a unique and outstanding heritage, a quantitative memory for the territory that is a rare fortune to possess. The analysis of historical data provides important information in various fields like agriculture, industrial and tourism planning. The study of long series also takes on particular significance in relation to the analysis of possible climate change caused by man.
Bra, city of Piedmont (NW Italy), has this wealth of information thanks to the naturalist Federico Craveri (1815-1890) who started in 1862 the meteorological measurements continued after by the Directors that have occurred at Craveri Museum.
In this work the analysis of daily series of maximum and minimum temperature and precipitation from 1862 to 2009 starts with quality control of the series (Zhang et al., 2004). The quality control highlights some wrong values (minimum temperature higher than maximum temperature or negative precipitation) due to incorrect transcription of data.
Later we have applied the homogeneity test SPLIDHOM (SPLIne Daily HOMogenization, Gruber et al., 2008) based on cubic regression that has allowed us to identify and correct the inhomogeneities in the daily series. The availability of daily homogeneous series has allowed us to begin a detailed climatic analysis aiming at identifying the climate change occurred in the territory over the past 149 years.
The climatic analysis has been carried out through the study of climate indices developed by the Expert Team for Climate Change Detection Monitoring and Indices (ETCCDMI). The use of climate indices has allowed us to assess not only the variations on the average values of the meteorological variables but also the changes of the extremes values that, in most cases, have a profound impact on the society and the economy (Morberg et al., 2005 e Tank et al., 2003).
For each series and each index, trends over different time scales (seasonal and annual) were calculated in order to identify the variations of the variables. The parametric Mann-Kendall test was applied to assess the statistical significance of the trends (Sneyers, 1990).

Session Number: P3v
Presenting Author: Thomas Gutermann
Author Email: t.gutermann@bluewin.ch
Author Affiliation: Former Director MeteoSwiss, Zurich
Co-Author: Hans Richner
Co-Author Affiliation: Institute for Atmospheric and Climate Science, ETH Zurich
Abstract Title:
Reconstruction of foehn durations from 1864 to 2008 from three daily climate observations
Abstract:
For the foehn station Altdorf, a long time series with three daily observations (fohn/no foehn) is available since 1864. Starting in 1984, hourly observations of foehn based on the automatic network became available, while the three classical observations were continued.
An attempt was made to reconstruct the actual duration of foehn (i.e. the number of foehn hours) for the time prior to 1984. In order to improve the quality of a reconstruction, hourly foehn occurrences were manually extracted form recordings for the period 1955 to 1983, hence parallel observations are now available from 1955 to 2008.
First, the correlation function between the number of foehn hours with the foehn observations was calculated using the 53 years of parallel observations. The correlation coefficient for yearly sums is very high (>0.95). Subsequently, using this function, the number of foehn hours for each year since 1864 was calculated. As could be expected, the year-to-year variation of the time series of the classical foehn observations and the upscaled high-resolution time series with foehn duration are very similar.
Due to the high variability of foehn occurrence from year to year, no trend can be observed as of now. Manual observations are gradually disappearing, and the three foehn observations per day have already been terminated. They are being replaced by automatically retrieved, hourly occurrences. With the results presented, it will be possible to reliably construct a continuous time series of foehn occurrence also in the future.

Session Number: P3w
Presenting Author: Wolfgang Loibl
Author Email: wolfgang.loibl@ait.ac.at
Author Affiliation: AIT, Austrian Institute of Technology
Co-Author: I. Anders(2), H. Formayer(3), A. Gobiet(4), P. Haas(3), Ch. Matulla(2), I. Nadeem(3), I. Schicker(3), W. Schöner(2), M. Suklitsch(4) and J. Züger(1)
Co-Author Affiliation: (1) AIT, (2) ZAMG, (3) BOKU, (4) WegCenter
Abstract Title:
Evaluation of regional climate simulations using COSMO-CLM and MM5 for Austria and the Alpine Region
Abstract:
Austrian policy makers, as well as the climate change impact research community and the society as a whole request information on changes in the climate during the last years and especially in the near and distant future. Estimation and quantification of changes in climate parameters and indices are a necessary precondition for adaptation and mitigation measures. Information on changes in the past of a wide range of relevant meteorological parameters where no long time series of observation sites are available, but also the estimation on future changes can only be provided by climate modeling.
Most regional climate model simulations covering the Alps are either of a coarse resolution or the simulated area does not contain the region of interest in a higher resolution.
Within the national project reclip:century we try to address this topic to regional climate simulations for the time frame of 1961 to 2000 and 2000 to 2050 covering the Greater Alpine Region (GAR) with a horizontal resolution of 10 km. The lateral boundary conditions for the control runs and the scenario runs are provided by two global climate models (ECHAM5 and HadCM3). Furthermore, ERA40 reanalysis data is used for the hindcast simulations.
The model results of both RCMs will be evaluated against gridded observation data provided in the ENSEMBLES project (Haylock et al., 2008) and to other gridded observation data sets (e.g., the Frei and Schaer, 1998, precipitation dataset). The analysis was carried out for the GAR subdivided into four climatic regions (HISTALP, Efthymiadis et al, 2006), for whole Austria and for seven Austrian subregions.
Beside common skill measures such as relative bias, temporal and spatial correlations on seasonal base, the BIAS skill-score and the Fischer skill-score are used to evaluate the overall performance of the models.

Session Number: P3x
Presenting Author: Imran Nadeem
Author Email: imran.nadeem@boku.ac.at
Author Affiliation: Institute of Meteorology, University of Natural Resources and Life Sciences (BOKU), Vienna,Austria
Co-Author: Irene Shicker, Herbert Formayer
Co-Author Affiliation: Institute of Meteorology, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria
Abstract Title:
Evaluation of Solar Radiation from RCMs within the Alpine Region based on station observations: Intercomparison of Reclip:century and ENSEMBLES simulations
Abstract:
The Radiative fluxes at the land surface are affecting many important physical processes. The net radiation is the primary source of energy for the land surface, and it directly affects surface temperatures and surface energy fluxes. In snow-covered areas, incoming radiation partially determines snowmelt, and the timing and magnitude of snowmelt has a significant effect on water balance. One of the aims of the climate group at our institute is to define and implement various evaluation techniques for assessment of RCM performance over the Alpine region. The evaluation of solar radiation simulated by two models used in the reclip:century project, the mesoscale model MM5 and COSMO CLM model, and their comparison with observed station radiation data from World Radiation Data Center (WRDC, http://wrdc.mgo.rssi.ru/) will be presented. The analysis will focus on the inner domain of the models which has horizontal resolution of 10 km and covers the Greater Alpine region (GAR). Furthurmore, comparison of radiation fluxes from these two models and different models from EU-project ENSEMBLES (www.ensembles-eu.org) will also be carried out.
The WRDC station data contains daily downward shortwave radiation measurements for varying record lengths between 1964 and 2010. For a majority of the stations in the GAR, the observations have at least 30 years of data. In addition, for some Austrian stations data from the Central Institute for Meteorology and Geodynamics (ZAMG) will be used. The analysis will be done on daily and seasonal bases. The monthly climatology of 30 years for the observed radiation as well as model simulated radiation will be compared. The frequency distribution of daily radiation for various stations will be shown.
Acknowledgment: reclip:century is funded by the Austrian Climate Research Programme (ACRP) of the Klima- and Energiefonds (Klie.En) of the Austrian Government.