Impact of Assimilating Multiple-Radar-Synthesized Three-Dimensional Winds and Retrieved Thermodynamic Fields Associated with Different Microphysical Schemes on Short-Term Rainfall Forecast in Mountainous Area

This research aims to investigate the impact of assimilating both dynamic and thermodynamic variables on the short-term rainfall forecast with different microphysical schemes in mountainous area. Two advanced and fully developed retrieval methods are utilized, and they are: WInd Synthesis System using DOppler Measurements (WISSDOM) and Terrain Permitting Thermal Retrieval Scheme (TPTRS). By using variational algorithms, three-dimensional wind fields are derived from multiple-Doppler-radar radial wind observations, then thermodynamic fields are retrieved from wind fields. In addition, the water vapor mixing ratio can also be estimated based on retrieved temperature. In our methods, the influence of topography is considered, which is important when the extreme precipitation is induced by interaction between weather systems and complex terrain.

The targeted case is from the IOP#8 during SoWMEX field experiment held in Taiwan. Results of the retrievals reveal that strong reflectivity coincides with upward motion and convergence along terrain, and is near the regions with negative/positive temperature/pressure perturbations, indicating the existence of a cold cool. Experiments to evaluate the performance of model short-term (0-6h) quantitative precipitation forecasts (QPF) using four microphysical schemes (i.e. GCE, WSM6, WDM6, MOR) are conducted. The results demonstrate that the magnitude of maximum precipitation can be reasonably captured, and the model-predicted major rainfall areas agree well with observations. Our approach does not need a long assimilation window, and requires only two volume scans radar data.