Gang Chen1, KunZhao1*, Guifu Zhang1,2
1Key Laboratory for Mesoscale Severe Weather/MOE and School of Atmospheric Science, Nanjing University, Nanjing, China
2School of Meteorology and Advanced Radar Research Center, University of Oklahoma, Norman Oklahoma 73072, USA
In this study, the capability of the polarimetric radar to estimate summer rainfall in Eastern China is explored using data collected from a C-band polarimetric Doppler radar (NJU_CPOL) and a two-dimensional video disdrometer (2DVD) during the Observation, Prediction and Analysis of Severe Convection of China (OPACC) field campaign in 2014 and 2015. Three different rainfall estimators, R(Z), R(Z,ZDR) and R(KDP) are derived from 2DVD observations, and then are verified against gauge observations with three different types of organized convective systems, that are a Meiyu precipitation system, a typhoon rainband, and a squall line.
Results show that R(KDP) produces the best rainfall estimation for all rain cases, while R(Z) performs the worst compared with the rain gauge observations. The scatter plots of ZDR vs KDP *105/Z ,which is usually used for characterizing precipitation physics, show that the warm rain-coalescence process is dominant in Meiyu and typhoon, while the melting of graupel and hail contributes strongly to rainfall in Squall line. The different precipitation physics also cause the evident variations in mean diameters (Dm) and liquid water content (LWC) among three cases. The typhoon rainband has the largest LWC, consisting of relatively small drops while the squall line contains the largest drops. Therefore, the high variations of raindrop size distribution (DSD) in different types of mesoscale convective systems can be mainly responsible for the case-dependent QPE performance using any single radar rainfall estimator. The trade-offs among different rainfall estimators indicate the potential benefit of a composite rainfall estimator.