The impact of TRMM PR algorithm updates and user methodologies on the tropics-wide stratiform rain fraction

Stratiform rain fractions can be calculated for the tropics using Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data providing information on the spatial variation of rainfall contribution from both stratiform and convective rain types as well as insight into the associated heating profiles important in driving atmospheric circulations. Several factors can impact the stratiform rain fraction results including the resolution of the data, the method of convective and stratiform separation, the height the separation is done at, and the Z-R relation used. In particular, this poster highlights changes to the datasets created by updates to the TRMM 2A23 (rain classification) and 2A25 (attenuation-correction and rain estimation) algorithms that impact stratiform rain fraction results. Updates made to the 2A23 algorithm, for instance, between version 6 (V6) and version 7 (V7) include the introduction of new criteria for pixel classification resulting in additional stratiform and convective rain types. Overall, a shift of shallow non-isolated pixels from stratiform to convective rain types is seen between V6 and V7 thereby reducing the overall tropics-wide stratiform rain fraction. Updates to the 2A25 algorithm for V7 include the introduction of a new drop size distribution (DSD) model and the re-introduction of non-uniform beam filling (NUBF). These changes alter reflectivity and rain rate values and can contribute to changes in the tropics-wide stratiform rain fraction.