Nowcasting of stratiform rain exploiting radar signatures in the dendritic growth layer, microphysical retrievals and spectral bin modelling
An introduction to radar polarimetry and its benefits for quantitative precipitation estimation, data assimilation, and numerical weather prediction is provided with a focus on most recent implications for nowcasting. Nowcasting of imminent precipitation enhancements is possible based on radar signatures indicating snow generation in the dendritic growth layer (DGL) located at temperature levels around -12°C. As a first step, it is assumed the precipitation flux does not change much on the way down to the surface. Trajectories of snow generated aloft down to the surface are constructed from wind profiles derived from radar-based velocity azimuth displays (VAD) to narrow down the location where the DGL-generated snow reaches the surface as rain. The comparison of DGL-derived snow precipitation flux S(IWC) with both surface reflectivity-derived and gauge-observed rain rates at the expected locations and times show already fairly good agreement. However, as a second step, processes modifying the precipitation flux from the DGL down to the surface like sublimation of ice below the DGL and evaporation of rain below the melting layer (ML) are estimated using spectral bin modeling initialized with radar-derived particle size distributions. A strategy for a DGL-based nowcasting routine of stratiform rain is presented.
PD Dr. Silke Troemel
Institute for Geosciences und Meteorology
Institut für Meteorologie und Klimaforschung (IMK-TRO)
Tel: 0721 608 43356
Mail:doris stenschke∂kit edu