Characteristics of radar observed rain cells in Germany

The German Weather Service (DWD) recently upgraded the radar network of 12 C-band radars to dual polarization. In this study, the data from the DWD network is processed into a 3D composite, that includes the following parameters: horizontal reflectivity (Zh), differential reflectivity (Zdr), specific differential phase (Kdp), correlation coefficient (Rhohv), 2D rain rates, number of lightning strikes, and some 2D cloud parameters from MSG-SEVIRI . A 3D tracking algorithm (Meanie3D) is applied to the reflectivity field to follow rain cells over their lifetime. The distribution of number of cells in classes of lifetimes shows sharp decrease in number with increase in cell duration, meaning that short-lived cells are more prevalent. However, we will show that even though their number is small, long lived cells have a major impact, accounting for a big portion of total rain and rain areal coverage. The duration of cells also seems to be related to intensity; for instance, the longer duration cells present higher values of maximum reflectivity, maximum rain rate and maximum altitude. Whether they live longer because of intensity or vice-versa is a question we will try to answer. In addition, we analyze Zdr columns (size and altitude) and possible link to enhancements in surface rainfall. We do this by means of time lagged correlations. Long lived or large clusters show a maximum correlation at about 5 to 10 minutes lag, while cells with short lifetimes and small sizes do not show a particular pattern. This short time lag (compared to previous studies) appears to be due to weaker updrafts that are in general present in this region. The weaker updraft should explain the smaller time lag, since the large particles cannot be maintained by the updraft strength and therefore fall to the surface faster than they would in a stronger updraft. The fact that the lagged effect of updraft on the surface rainfall is only observed for longer lived cells is another evidence that duration is linked to strength of the storm. Nevertheless, a preliminary analysis of the very intense Pentecost storm that occurred in June 2014 indicated lead times up to 1 hour between Zdr columns and surface reflectivity enhancements.