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Universität Hohenheim
Institut für Physik und Meteorologie (IPM) 

Project team: Volker Wulfmeyer, Marcus Radlach, Andreas Behrendt, Hans-Stephan Bauer

Activities within

Development and application of a new generation of ground-based, 3-d scanning, mobile remote sensing systems

A 3-d scanning water vapour differential absorption lidar (DIAL) system is under development. This system will be able to measure 2-d fields of water vapour with a range resolution of 100-1000m and a time resolution of 1 min within a range of +/- 20 km. Also wind fields can be measured using autocorrelation analyses of aerosol fields. Profiles of turbulent water vapour transport and turbulence statistics up to the fourth-order can be obtained. Water vapour profiles up to the lower stratosphere can be observed. Water vapour DIAL measurements shall be combined with high-resolution temperature measurements using a Raman lidar, so that 3-d measurements of relative humidity as well as atmospheric stability become possible.

Innovative and synergetic use of active remote sensing systems within field campaigns

The potential of scanning and mobile active instruments for water vapour, temperature and wind shall be explored in order to find optimal operation strategies. The goal is to close the gaps in knowledge about the initial fields determining the convective environment. This shall be achieved by application of several end-to-end performance models which have been developed in connection with the design of ground-based, airborne and space-borne lidar systems. It will be investigated how clear-air lidar systems should be combined with cloud radar and precipitation radar systems in order to get the maximum amount of information concerning the variables controlling the initiation and the development of convective systems. The measurement of the clear-air environment using lidar shall be extended in clouds and rain using radar wavelengths.

Impact studies using mesoscale models

The impact of remote sensing systems on model performance (LM, MM5) shall be assessed. Operators for using their data will be developed and data collected during field campaigns will be assimilated in the models. The impact of active remote sensing systems on the model performance will also be investigated by Observing System Simulation Experiments (OSSEs) using synthetic data. This will allow to study different strategies for deploying networks of active remote sensing systems most effectively.

High-resolution modeling studies at UHOH using the mesoscale numerical weather prediction model MM5

To prepare the use of the MM5 modelling system for real-time forecasting during the field campaign COPS in summer 2007, first high-resolution simulations has been performed in the COPS region. As the first (of several) case studies, the development of convection on June 19th 2002 in south-western Germany was investigated.

The situation was characterized by a slow-moving trough-ridge system in the middle troposphere. The trough is located over the eastern Atlantic with a corresponding low pressure system at the surface north of the British Isles, whereas the ridge is located over the Eastern Alps. In the lower troposphere only weak pressure gradients occur whereas in the middle troposphere strong pressure gradients and correspondingly strong south-westerly winds appeared. During the day of June, 19th the trough system slowly approaches from the west paving the way for the classical situation in which severe pre-frontal convection occurs in south-western Germany.
For the simulations a triple-nested MM5 Version 3.7 configuration with horizontal resolutions of 9, 3, and 1 km was used. Initialization and boundary forcing are provided by ECMWF analysis, available every 6 hours. Nesting of the three model domains is done in a 2-way-interactive configuration, proposed to be the best set-up in orographically structured terrain. The model forecast was started at 00 UTC, 19th of June 2002 and runs for 18 hours. A most sophisticated set of parameterizations was used to allow an as realistic as possible simulation of the convective event.
Two types of experiments were carried out. First data from drop sondes are assimilated into the MM5 FDDA system to investigate the influence of observations on the forecast as compared to the forecast only driven by the ECMWF analysis. Here, a clear impact was seen. However, since only the data of 12 soundings were used, the changes are small. Further experiments using the more sophisticated 3DVAR and 4DVAR schemes MM5 provides are planned for the future.
A second set of experiments investigated the influence of the choice of the initial time on the forecast results. This is interesting since a different amount of observations is used at different initial times in the ECMWF analysis. Here, clearly larger differences between the two forecasts exist. The convective activity simulated in the forecast started earlier is shifted to the east and stronger than in the forecast started 6 hours later. Furthermore, a larger region is affected by the convection. This suggests that the timing of the development is different using different initial times.

3-D visualization of the development of convection over the Black Forest in an
MM5 forecast using 1-km horizontal resolution. The coloured layer shows the
height of the topography with the Vosges Mountains in the foreground and the
Black Forest in the background. The 3-D surfaces surround regions in which
different hydrometeor classes appear (white = cloud liquid water; blue = rain;
yellow = cloud ice, and green = snow).