C. Kottmeier

HYMEX , a 10-year Multidisciplinary Program on the mediterranean water cycle.

The Mediterranean countries are experiencing important challenges related to the water cycle, including water shortages and floods, extreme winds, and ice/snow storms, that impact critically the socioeconomic vitality in the area (causing damage to property, threatening lives, affecting the energy and transportation sectors, etc.). There are gaps in our understanding of the Mediterranean water cycle and its dynamics that include the variability of the Mediterranean Sea water budget and its feedback on the variability of the continental precipitation through air–sea interactions, the impact of precipitation variability on aquifer recharge, river discharge, and soil water content and vegetation characteristics specific to the Mediterranean basin and the mechanisms that control the location and intensity of heavy precipitating systems that often produce floods. The Hydrological Cycle in Mediterranean Experiment (HyMeX) program is a 10-yr concerted experimental effort at the international level that aims to advance the scientific knowledge of the water cycle variability in all compartments (land, sea, and atmosphere) and at various time and spatial scales. It also aims to improve the processes-based models needed for forecasting hydrometeorological extremes and the models of the regional climate system for predicting regional climate variability and evolution. Finally, it aims to assess the social and economic vulnerability to hydrometeorological natural hazards in the Mediterranean and the adaptation capacity of the territories and populations therein to provide support to policy makers to cope with water-related problems under the influence of climate change, by linking scientific outcomes with related policy requirements.

The Convective and Orographically Induced Precipitation Study:A Research and Development Project of the World Weather Research Program for Improving Quantitative Precipitation Forecasting in Low-mountain Regions

Abstract The international field campaign called the Convective and Orographically-induced Precipitation Study (COPS) took place from June to August 2007 in southwestern Germany/eastern France. The overarching goal of COPS is to advance the quality of forecasts of orographically-induced convective precipitation by four-dimensional observations and modeling of its life cycle. COPS was endorsed as one of the Research and Development Projects of the World Weather Research Program (WWRP), and combines the efforts of institutions and scientists from eight countries. A strong collaboration between instrument principal investigators and experts on mesoscale modeling has been established within COPS. In order to study the relative importance of large-scale and small-scale forcing leading to convection initiation in low mountains, COPS is coordinated with a one-year General Observations Period in central Europe, the WWRP Forecast Demonstration Project MAP D-PHASE, and the first summertime European THORPEX Regional...

The Convective Storm Initiation Project

The Convective Storm Initiation Project (CSIP) is an international project to understand precisely where, when, and how convective clouds form and develop into showers in the mainly maritime environment of southern England. A major aim of CSIP is to compare the results of the very high resolution Met Office weather forecasting model with detailed observations of the early stages of convective clouds and to use the newly gained understanding to improve the predictions of the model. A large array of ground-based instruments plus two instrumented aircraft, from the U.K. National Centre for Atmospheric Science (NCAS) and the German Institute for Meteorology and Climate Research (IMK), Karlsruhe, were deployed in southern England, over an area centered on the meteorological radars at Chilbolton, during the summers of 2004 and 2005. In addition to a variety ofground-based remote-sensing instruments, numerous rawinsondes were released at one- to two-hourly intervals from six closely spaced sites. The Met Office weather radar network and Meteosat satellite imagery were used to provide context for the observations made by the instruments deployed during CSIP. This article presents an overview of the CSIP field campaign and examples from CSIP of the types of convective initiation phenomena that are typical in the United Kingdom. It shows the way in which certain kinds of observational data are able to reveal these phenomena and gives an explanation of how the analyses of data from the field campaign will be used in the development of an improved very high resolution NWP model for operational use.

Roll Vortices and Boundary-Layer Development during a Cold Air Outbreak

The development of the boundary layer during a cold air outbreak in the FramStrait is documented by aircraft measurements. The convection was organisedinto roll vortices with aspect ratios increasing from 2.9 near the ice edgeto more than 6 at 100 km further downstream. This increase coincides with anincrease of the latent heat release in the cloud layer. The stability parameter-zi/L varies from about zero at the ice edge to 30 at a distance of 200 kmdownstream over open water where the satellite picture still shows cloudstreets. The increase is mainly due to the deepening of the boundary layer.The turbulent vertical sensible and latent heat fluxes near the surface amountto 400 W m-2 within a 300 km off-ice zone. 25% of the upward heat fluxin the subcloud layer is carried out by organised roll motions. Experimentswith a 2-dimensional non-hydrostatic model show a similar roll aspect ratio inthe first 50 km, but further downstream where condensational heating is moreimportant the modelled roll wavelengths are distinctly smaller than the observedones.

Regional transport and dilution during high-pollution episodes in southern France: Summary of findings from the Field Experiment to Constraint Models of Atmospheric Pollution and Emissions Transport (ESCOMPTE)

In the French Mediterranean basin the large city of Marseille and its industrialized suburbs (oil plants in the Fos-Berre area) are major pollutant sources that cause frequent and hazardous pollution episodes, especially in summer when intense solar heating enhances the photochemical activity and when the sea breeze circulation redistributes pollutants farther north in the countryside. This paper summarizes the findings of 5 years of research on the sea breeze in southern France and related mesoscale transport and dilution of pollutants within the Field Experiment to Constraint Models of Atmospheric Pollution and Emissions Transport (ESCOMPTE) program held in June and July 2001. This paper provides an overview of the experimental and numerical challenges identified before the ESCOMPTE field experiment and summarizes the key findings made in observation, simulation, and theory. We specifically address the role of large-scale atmospheric circulation to local ozone vertical distribution and the mesoscale processes driving horizontal advection of pollutants and vertical transport and mixing via entrainment at the top of the sea breeze or at the front and venting along the sloped terrain. The crucial importance of the interactions between processes of various spatial and temporal scales is thus highlighted. The advances in numerical modeling and forecasting of sea breeze events and ozone pollution episodes in southern France are also underlined. Finally, we conclude and point out some open research questions needing further investigation.In the French Mediterranean basin the large city of Marseille and its industrialized suburbs (oil plants in the Fos-Berre area) are major pollutant sources that cause frequent and hazardous pollution episodes, especially in summer when intense solar heating enhances the photochemical activity and when the sea breeze circulation redistributes pollutants farther north in the countryside. This paper summarizes the findings of 5 years of research on the sea breeze in southern France and related mesoscale transport and dilution of pollutants within the Field Experiment to Constraint Models of Atmospheric Pollution and Emissions Transport (ESCOMPTE) program held in June and July 2001. This paper provides an overview of the experimental and numerical challenges identified before the ESCOMPTE field experiment and summarizes the key findings made in observation, simulation, and theory. We specifically address the role of large-scale atmospheric circulation to local ozone vertical distribution and the mesoscale processes driving horizontal advection of pollutants and vertical transport and mixing via entrainment at the top of the sea breeze or at the front and venting along the sloped terrain. The crucial importance of the interactions between processes of various spatial and temporal scales is thus highlighted. The advances in numerical modeling and forecasting of sea breeze events and ozone pollution episodes in southern France are also underlined. Finally, we conclude and point out some open research questions needing further investigation.

A model of dust transport applied to the Dead Sea Area

We applied a parameterization for the emission of mineral dust particles which takes into account the relevant processes such as saltation and combines previous, physically based parameterizations. The size distribution of the soil particles is taken into account to describe the saltation. The emitted particles are described by three log-normal distributions with fixed standard deviations. A comparison of the results of a stand alone version of our parameterization with observations shows that despite tuning of model parameters there are still differences. Finally, we included the parameterization within our three-dimensional mesoscale model system for the area of the Dead Sea. The channelling effect of the Jordan Valley and stable stratification during the day modifies the horizontal distribution of the dust particles. At greater distances the size and the mass distributions of the particles is shifted towards smaller diameters due to sedimentation which is important for radiative feedback mechanisms. Sensitivity runs show the advantage of the parameterization which allows a time dependent ratio of the saltation and the emission flux at each grid point.

The convective and orographically-induced precipitation study

Abstract The international field campaign called the Convective and Orographically-induced Precipitation Study (COPS) took place from June to August 2007 in southwestern Germany/eastern France. The overarching goal of COPS is to advance the quality of forecasts of orographically-induced convective precipitation by four-dimensional observations and modeling of its life cycle. COPS was endorsed as one of the Research and Development Projects of the World Weather Research Program (WWRP), and combines the efforts of institutions and scientists from eight countries. A strong collaboration between instrument principal investigators and experts on mesoscale modeling has been established within COPS. In order to study the relative importance of large-scale and small-scale forcing leading to convection initiation in low mountains, COPS is coordinated with a one-year General Observations Period in central Europe, the WWRP Forecast Demonstration Project MAP D-PHASE, and the first summertime European THORPEX Regional...

Wind forcing and ice motion in the Weddell Sea region

The wind forcing on the ocean surface and temporal and spatial characteristics of ice motion are analyzed from data of automatic buoy stations, drifting for 14 months on ice floes in the Weddell Sea. Generally fluctuations with periods from 2 to 5 days, which are caused by synoptic scale atmospheric wind fields, primarily contribute to the variance of ice drift. Peaks in the spectra of ice motion are also found at 12 hours due to inertial motion and weak tidal effects, which are nearly coincident in this geographical region. Inertial motion is only missing in winter, when the ice concentration is high in the western branch of the Weddell Gyre, Semidiurnal peaks are stronger over the continental shelf than over the deep ocean. Diurnal peaks are weaker than semidiurnal peaks. They are found over the continental shelf and are missing over the deep ocean at the same time. The tidal motion reflects non-wind-related coupling between water and ice motion for periods of 1/2 to 1 day. The integral length scales of ice motion are between 550 and 680 km (longitudinal correlation) and between 360 and 540 km (lateral correlation), respectively, when the ice concentration exceeds eight tenths. In the marginal ice zone, the lateral length scale of ice motion is reduced to 270 km. The integral length scales of air pressure fields exceed the length scales of ice motion by a factor of at least 1.5. Longitudinal and lateral length scales of ice motion in the Weddell Sea are slightly smaller than those published for the Beaufort Sea, where the ice moves within a basin of similar diameter of approximately 1500 km. The smaller scales in the Weddell Sea presumably are due to differences of the forcing fields. About 70% to 95% of the variance of 12-hourly averaged drift velocities can be linearly related to the wind velocity, except when the mean wind speed drops below 3.5 m/s. The correlation with geostrophic winds is close to that with locally measured winds. The twelve-hourly averaged ice drift amounts to about 3.5% of the actual surface wind velocity at a height of 3 m or to about 1.6% of the geostrophic wind velocity, derived from surface pressure analyses. The drift/geostrophic wind ratio is 30% smaller in central winter with ice concentrations above nine tenths in the central Weddell Sea than during summer periods, when the buoys are closer to the coast, in the periphery of the gyre and in the marginal ice zone. The drift/local wind ratio scatters more than the drift/geostrophic wind ratio. The ice drift in winter for ice concentrations above eight tenths, on an average, is deflected by 20 degrees to the left of the surface wind direction and is parallel to the isobars. In summer under reduced ice concentrations, it deviates by 40 degrees to the left of the surface wind and by 10 to 15 degrees to the left of the geostrophic wind. For periods of 1 month, the ice drift is also linearly well correlated to geostrophic wind velocity. Winds in the Weddell Sea usually do not average out over longer time scales. Ocean currents are too weak to dominate mean ice motion.

On the importance of leads in sea ice to the energy balance and ice formation in the Weddell Sea

For a considerable coverage the energy balance of and ice formation by leads in sea ice in the Weddell Sea are evaluated on the basis of data obtained from drifting buoys for the winter periods from 1986 to 1994 and by using a kinematic-thermodynamic sea ice model.The net heat flux is defined as the sum total of radiative and turbulent fluxes.For thin ice the net turbulent flux is 3--4 times the net radiative flux.The contribution of the net heat flux through open and refrozen leads to the total net heat flux through sea ice is twice as large as the area contribution of open and refrozen leads to the total area covered with sea ice.In the eastern and central parts of the Weddell Sea, leads contribute some 30\% to the total energy flux from the ocean to the atmosphere.This flux increases from 10--15

Orographic Enhancement of Precipitation over Low Mountain Ranges. Part I: Model Formulation and Idealized Simulations

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