Quantitative precipitation estimation using specific differential propagation phase in typhoon system in Taiwan

To improve the accuracy of radar based Quantitative Precipitation Estimation (QPE) for typhoon systems in Taiwan, a new empirical R(K_DP) relation and a new K_DP correction method are proposed for C-band dual-polarization radars. It was reported that the drop size distribution (DSD) and drop shape relation (DSR) in typhoon systems presented unique characteristics in Taiwan. The existing R(K_DP) relations based on typical maritime or continental precipitation system may not be suitable for radar QPEs in the typhoon environment. A new relation between the rainfall rate and K_DP for C-band polarimetric radars is derived through numerical simulations in the current study. Another focus of this work is to develop a K_DP correction method based on analyses of vertical profiles of the specific differential phase. The corrected K_DP from high altitudes is used to replace the missing or unreliable K_DP at low altitudes caused by radar beam shielding. Both of the new R(K_DP) relation and correction method are tested and validated on two operational C-band polarimetric radars in Taiwan with typhoon cases of Morakot and Fanapi. With the proposed techniques, the C-band dual-polarization radars were shown to provide more accurate QPEs than S-band single-polarization operational radars.