Dual-polarization radar rainfall estimation over warm tropical oceans

The impacts of Tropical Warm Pool rain variability on the dual-polarization radar variables and their utility for rainfall estimation in this key climate region are investigated. A 1.5-year W. Pacific disdrometer dataset provided high resolution rain rate (R) and drop size distribution (DSD) parameters to simulate radar variables (Z_h, Z_dr, K_dp) at X, C, and S band. A previous study using the same dataset found that tropical, maritime convection is composed of more numerous, higher liquid water content DSD, with smaller median drop diameter for a given R, compared to stratiform rain. This resulted in lower Z_dr for a given Z_h, and lower Z_dr for a given K_dp in maritime convection compared to stratiform rain. In contrast, intense continental convective rain made up of fewer, but larger rain drops can exhibit very high Z_dr for a given Z_h. Despite high liquid water content, K_dp, Z_dr, and Z_h ranges were also lower in maritime convection compared to continental convection. New equations relating K_dp(z), R(z, ζ_dr), R(K_dp), and R(K_dp, ζ_dr) at X, C, and S band were developed to account for this tropical, oceanic and C/S DSD variability. The new polarimetric R equations outperformed z-only methods individually and in optimization algorithms. Polarimetric radar equations were demonstrated to be more resilient to convective/stratiform and global DSD variability than z-only equations.