Application of QVP Method to Winter Precipitation Observation Based on Polarimetric Radar

Abstract

Winter precipitation events, especially those involving transitions of precipitation type, continue to pose a formidable forecasting and nowcasting challenge to operational meteorologists. The polarimetric radars provide unique insight into microphysical processes in clouds and precipitation. Using polarimetric radars in conjunction with thermodynamic information is a promising way for better winter precipitation detection. To explore the microphysical characteristic and the internal structure of winter precipitation over eastern coast of China, the data collected by the WSR-88D polarimetric radar at Nanhui, Shanghai are exploited by the quasi-vertical profile (QVP) method. The QVP method involves azimuthal averaging of radar reflectivity factor at horizontal polarization(ZH), differential reflectivity(ZDR) and the copular correlation coefficient (ρhv) at high antenna elevation, presenting QVPs in a height-time format. QVP generation is an efficient way to examine the temporal evolution of microphysical processes governing precipitation production and to display physical links between polarimetric signatures aloft in the ice-phase or mixed-phase parts of the clouds. In 3 different synoptic system governing snow cases affecting Shanghai, the QVPs retrieved from dual-polarization radars at elevations of 19.5ånd 9.9åre demonstrated to successfully monitor the evolution of melting layer and Bergeron process. They also provide opportunities to discriminate between the processes of snow aggregation and riming with the joint analysis of reanalysis data and observations of radio sounding, auto weather station, disdrometer and wind profiler radar. The vertical observation by cloud radar data is used to compare with QVP retrieved profile. Additionally, for discontinuous or multi-scale synoptic precipitation, a selected azimuthal averaging QVP technique is introduced to separate QVPs into before and after the synoptic system for detailed comparisons and monitoring microphysical processes leading to precipitation formation. The method is demonstrated to monitor important microphysical signatures as well as following precipitation development. In conclusion, the procedure for generating quasi-vertical profiles of polarimetric radar variables is very simple and straightforward, and the QVP plots in the height-time format can be produced in real time for operational polarimetric weather radars as a standard product, which is very easy to implement and very promising to use along with traditional weather radar products of PPIs and reconstructed RHIs. The QVP methodology is particularly effective because of its local coverage and high precision as well as its potential for nowcasting.

Keywords

• quasi-vertical profiles
• polarimetric radar
• microphysical characteristics