U. Corsmeier

HyMeX-SOP1: The Field Campaign Dedicated to Heavy Precipitation and Flash Flooding in the Northwestern Mediterranean

The Mediterranean region is frequently affected by heavy precipitation events associated with flash floods, landslides, and mudslides that cause hundreds of millions of euros in damages per year and often, casualties. A major field campaign was devoted to heavy precipitation and flash floods from 5 September to 6 November 2012 within the framework of the 10-year international HyMeX (Hydrological cycle in the Mediterranean Experiment) dedicated to the hydrological cycle and related high-impact events. The 2- month field campaign took place over the Northwestern Mediterranean Sea and its surrounding coastal regions in France, Italy, and Spain. The observation strategy of the field experiment was devised to improve our knowledge on the following key components leading to heavy precipitation and flash flooding in the region: i) the marine atmospheric flows that transport moist and conditionally unstable air towards the coasts; ii) the Mediterranean Sea acting as a moisture and energy source; iii) the dynamics and microphysics of the convective systems producing heavy precipitation; iv) the hydrological processes during flash floods. This article provides the rationale for developing this first HyMeX field experiment and an overview of its design and execution. Highlights of some Intense Observation Periods illustrate the potential of the unique datasets collected for process understanding, model improvement and data assimilation.

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.

Ozone concentration jump in the stable nocturnal boundary layer during a LLJ-event

Abstract During the field campaign performed within the SANA-project (readjustment of the atmosphere in the five new federal states of the Federal Republic of Germany) at a flat, rural site in eastern Germany, several cases of a jumplike increase of ozone at the surface under stable conditions during the nights have been observed. The concentration jumps of ozone are on the order of 1 2 to 2 3 of the days maximum and the level is significantly higher than under normal conditions with stable stratification. The cases are correlated with an increase in wind speed, wind shear and a downward flux of ozone. Inthe case selected here, the increase in turbulence is caused by the evolution of a low-level jet (LLJ) with the core just above the top of surface inversion. The analysis of wind profile measurements at the aerological stations in north-eastern Germany reveals a spatial extension of the low-level jet of up to 600 km in lenght and 200 km in width. Thus the significance of the LLJ on the transport capability of the atmosphere is twofold: due to the large spatial extent of the LLJ and the high wind speed at the jet core level air pollutants are transported over hundreds of kilometers during one night. Secondly, due to the strong wind shear between the jet core and the ground pollutants can be mixed to the ground far away from the release area.

Aspects of the convective boundary layer structure over complex terrain

Abstract Measurements are presented of the development of the convective boundary layer in the transition zone from the Upper Rhine valley to the Northern Black Forest during one special observation period of the TRACT campaign conducted in September 1992. The data used in this study were obtained from airborne instruments as well as from ground-based stations. The analysed boundary layer structure shows a strong influence of the underlying terrain. Until noon, a nearly terrain following capping inversion developed. However, advective processes proved to play an important role in the boundary layer structure over the hilly terrain. So, the large-scale air flow caused suppression of the convective boundary layer growth at the mountain ridge by forcing the capping inversion towards the elevation of the terrain. A mountain induced secondary circulation system was observed on the western facing slopes of the Black Forest. This secondary circulation system affected the heat budget and therefore the growth of the convective boundary layer over the mountain slopes. The advection of cold air by up-slope winds lowered the heating rate near the ground and was able to generate an inversion above the up-slope wind layer. In the late afternoon, the terrain following structure of the capping inversion diminished and the capping inversion tended to form a horizontal plane. Prognostic formulae for boundary layer growth are discussed for different sites of the terrain. While in the valley good agreement is found between calculated and observed boundary layer depths, the calculations for the mountain ridge overestimate the obserations by up to a factor of 5 if a boundary layer growth equation derived for homogeneous terrain is used.

Temporal evolution and spatial variation of the boundary layer over complex terrain

Abstract The temporal and spatial evolution of the convective boundary-layer has a strong effect on air pollutant dispersion, especially under inhomogeneous conditions with varying orography and/or land use. During the TRACT experiment the evolution of boundary-layer height in space and time was measured by radiosondes and aircraft during three special observation periods (SOPs). The observations show that (a) The boundary-layer height follows the height of the underlying orography. The correlation between boundary-layer height and orography holds best in the morning hours, but decreases slightly during the afternoon. This result confirms with previous observations on a smaller scale, which show that the PBL top confirms to the underlying orography until the boundary-layer depth exceeds the characteristic scale of the obstacle. (b) Coincident with the spatial variation of the boundary-layer height, a strong spatial variation of air pollutants can be observed. (c) On two of the three SOPs surface fog-covered parts of the TRACT area (the upper Rhine valley) until noon. Due to the reduced surface heating the boundary-layer height in the foggy areas was much lower than in the clear areas.

Influence of valley winds on transport and dispersion of airborne pollutants in the Freiburg‐Schauinsland area

The change of the concentration of trace gases in a natural environment depends on both chemical and meteorological conditions. To quantify the contribution of meteorological processes, such as transport and dispersion, chemical and meteorological processes must be assessed separately. In June 1996 the Schauinsland Ozone Precursor Experiment (SLOPE) was carried out to investigate the behavior of ozone and its precursors as a function of time in a valley between Freiburg in the Rhine Valley and Schauinsland in the Black Forest [Volz-Thomas et al., this issue]. The main purpose of this contribution is to calculate the influence of transport and dispersion on the change of the concentration of airborne pollutants in a propagating air mass. Therefore (1) an inert tracer, SF 6 , was released, and (2) meteorological measurements were performed to investigate the valley wind regimes and the evolution of the mixed layer. Here are the main results of the experiment: Clear-sky conditions caused upvalley winds to be generated in the various valleys in the morning. These upvalley winds led to the transport of polluted air and SF 6 from Freiburg through the Zarten Basin and the side valley (Grosses Tal) up to the Schauinsland hill. The propagation through the Grosses Tal took 90 ± 5 min, which gives a propagation rate of approximately 1.3 m s -1 . The dilution factor for SF 6 between the entrance and the outlet of the valley was approximately 9. This dilution factor could not only be explained by the continuous growth of the boundary layer during the propagation time of the tracer from the entrance to the outlet of the valley, but additionally by flow splitting and mountain venting [Fiedler et al., this issue].

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.

Comparison of measured and calculated motorway emission data

Abstract A comprehensive field campaign was carried out to check the quality of modelled on-road emissions of NOx and CO by comparing them with real-world emissions on a motorway in the southwestern part of Germany. Three different sets of emission data were determined for a section of the motorway A 656 that connects Mannheim and Heidelberg. First, emission data were pre-calculated, that means before the field campaign took place, using literature data for traffic volume, types of vehicles and driving speeds. Second, detailed traffic measurements during two intensive measurement phases were used to calculate improved emission data based on the actual traffic situation. Third, real-world emission data were determined by meteorological and chemical measurements. It shows that the differences of the pre-calculated emission data and the emission data improved by the traffic measurements differ by less than 15% in case of CO and approx. by 35% in case of NOx. A comparison of the observed emissions with the calculated ones gives an agreement for NOx within the error bars. For CO, however, a discrepancy by a factor of two was found. The real-world emissions were much higher than calculated.

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...