Evaluating Satellite Rainfall Retrievals for Tropical Convective Regimes: Case Analysis from Kwajalein Atoll

Abstract:

Validation of oceanic retrieved rainfall from satellite remains a difficult task due to limited surfaced-based observations of precipitation. Currently, the dual-polarimetric S-band radar located on the Kwajalein Atoll (KPOL) is the only fully continuous operational radar in a tropical ocean setting – making the Kwajalein site an invaluable tool for evaluating tropical oceanic precipitation retrievals from the TRMM and GPM missions. Perturbations in oceanic rainfall during El Niño time periods lead to large discrepancies in passive and active microwave rainfall retrievals, which are linked to regional variations in convective organization (i.e. changes in isolated convection and mesoscale convective systems). The Kwajalein ground validation program provides the opportunity to validate the instantaneous TRMM rain products as a function of convective regime. To investigate regime-based relationships, multiple case studies are observed from 2008-2014 encompassing shallow convection, deep isolated convection, organized convection, and stratiform precipitation. The main objectives are to observe which rain rates retrieved from either PR or TMI algorithms are in agreement with KPOL-derived values and if distinct biases exist between TMI and PR as a function of convective regime. Among the cases examined, biases with KPOL are largest in deep isolated convection for TMI and PR retrievals. Furthermore, TMI tends to overestimate PR and KPOL estimations in broad stratiform precipitation. Examination of the GPROF rain rate retrieval and a comparison with rain estimates from the GPM core satellite will be used to further investigate the differences between the TRMM and KPOL-derived rain rates.