Classifying Precipitation Types in Tropical Cyclones Using the NRL 37GHz Color Product

The tropical cyclone (TC) webpage developed by the U.S. Naval Research Lab (NRL) has been widely used by the community for real-time TC monitoring and forecasting. Using 14years of Tropical Rainfall Measuring Mission Microwave Imager and Precipitation Radar data in TCs, precipitation/convection types are quantitatively classified based on vertical radar profiles corresponding to seven different color regions in the NRL's 37GHz color composite product. The bright cyan and all pink (including pure pink, bright cyan/pink, and weak cyan/pink, and green/pink) regions are identified as nearly 100% precipitative regions. The bright cyan and pure pink regions are shallow and deep convective precipitation, respectively, while the green/pink, weak cyan/pink, and bright cyan/pink regions are mainly stratiform rain. Eighty-four percent of pixels in the weak cyan region are precipitating, including either shallow convective, stratiform, or anvil precipitation. Seventy-six percent of pixels in the green region are nonprecipitating pixels, and 24% of them are very lightly precipitating pixels, which could be contaminated from clouds with high liquid water content. The ability to perform TC precipitation-type analysis of this detail (convective versus stratiform and deep versus shallow) was previously only possible using radar-based classification algorithms. Using the 37GHz precipitation-type analysis, a significant increase of coverage of stratiform precipitation and shallow convection in the inner core is found between 3 and 21hr before the onset of TC rapid intensification.