Evaluation of Mesoscale Events using dual-Polarization and Doppler Radar Observations

Abstract

Dual-polarization and Doppler radar observations allow for the detailed analysis of microphysical and dynamic processes in clouds and precipitation. The dual-polarization Doppler C-band weather radar POLDIRAD (polarization diversity Doppler radar) was installed at the DLR site Oberpfaffenhofen near Munich in Southern Germany in 1986. It was the first fully C-band polarimetric weather radar in Europe and has been used for various research projects and is operated for research only (Schroth et al., 1988). Meanwhile a number of upgrades of the system have been performed. Research applications and field campaigns showed the value of modern weather radars for the understanding of the microphysics and dynamics of meso-scale systems like thunderstorms and cold-fronts. In the presentation we will first introduce principles of dual-polarization and Doppler techniques and then present some examples of observations from a number of field campaigns performed in Southern Germany. To investigate the influence of the Alps on cold-frontal systems a single-Doppler wind field retrieval system was developed and applied during the German Front Experiment. A cold front with a narrow rain-band was observed in the morning of 19 Dec. 1987. As the front approaches the Alps from the North-West, the narrow rain-bands were deformed and finally the rain-bands were dissolved. With the wind field retrieval technique it was possible to show that the warm conveyor-belt preceding the cold front was degraded when the front reached the Alps and thus preventing the front to cross the Alps (Hagen, 1992). The influence of mountains on the initiation of convection was the focus of the COPS campaign in 2007 (Wulfmeyer et al., 2008). The initiation of convection depends not only on the available convective energy and humidity, but also on the flow over and around a mountain. A study of numerous events in the vicinity of the Vosges Mountains in Eastern France showed that the Froude number of the flow controls whether convection is initiated over the mountain ridge or on the lee side of the mountain (Hagen et al., 2011). During the COPS campaign an outstanding isolated single-cell thunderstorm was observed. This storm developed over the Black-Forest Mountains when a convergence line crossed the mountain ridge. Almost no other convection was observed during that day. With the help of dual-polarization observations and multiple-Doppler analysis the life-cycle was analyzed in detail. Additional observations by satellite and lighting detection system provided further understanding of the initiation and life-cycle of system (Schmidt et al., 2012).