The Impact of Different Precipitation Types on the Polarimetric Radar QPE Using Specific Attenuation

The Quantitative Precipitation Estimation (QPE) algorithm using the specific attenuation (R(A)) has the advantages of immune to attenuation, radar miscalibration, wet radome, and partial beam blockage. Although the R(A) algorithm is more robust to the variability of drop size distributions (DSD) compared to other radar rainfall relations, its performance could be further enhanced if R(A) approach could be automatically adjusted according to different precipitation types. This work investigates the impact of the precipitation types on R(A) approach for both S-band and C-band polarimetric radar through simulation and real cases study. In the simulation, radar variables (such as Z, A, and specific differential phase K_DP) are first calculated using T-matrix method with DSD data collected from four impact-type Joss-Waldvogel disdrometers (JWD) located in Taiwan. More than 312 hours DSD data from stratiform, convective, and tropical precipitations are used in this work. The variations of A field estimation and R-A relationships for different precipitation types are then studied. For S-band polarimetric radar, the estimate of A from the ZPHI procedure requires tuning the net ratio α = A/K_DP along the radar beam. The coefficient α could be estimated based on the rain type and the slope of the Z–Z_DR dependency in a particular rain event. This conclusion is consistent with previous studies. For C-band radar, the coefficient α is not sensitive to the precipitation types, but the R-A relationships for typical stratiform and convective could be significantly different. This work proposed adjusted R(A) approaches for both C-, and S-band polarimetric radar located in Taiwan. Their performances of modified approaches are evaluated using stratiform, convective, and typhoon precipitation events.