Tropical orographic rainfall regimes according to the Tropical Rainfall Measuring Mission

This study seeks to (1) examine the performance of TRMM precipitation radar (PR) and microwave imager (TMI) rainfall retrievals in regions of heavy precipitation near complex terrain in the tropics, and (2) compare the vertical and horizontal structure of precipitation systems near tropical mountain ranges. For this study, we will examine 11 years (1998-2008) of data over the Western Ghats, Himalayas, tropical Andes, Sierra Madre Occidental, and Hawaii to examine retrieval uncertainties in both the TRMM radar (2A25) and passive microwave (2A12) retrievals. Using available ground validation networks, we will analyze relative bias characteristics of both TRMM algorithms, as well as examine issues related to algorithm assumptions and mechanics in these regions. For the radar algorithm these include the masking of surface clutter and attenuation correction, while for the passive microwave retrieval these include the masking of artifacts and the relationship between ice scattering signatures and estimated surface rainfall rate.

The second portion of the study will examine the vertical and horizontal structure of radar echoes in precipitation systems near these mountain ranges. We will examine how vertical structure within precipitation systems varies as a function of height and time of day using statistical analysis and the “precipitation feature” approach. We will also examine reanalysis data to investigate how the vertical structure of wind shear, moist instability, and moisture availability impacts the structure of precipitation systems in the selected regions. Implications for characteristic variations in microphysical processes and rainfall production will be discussed, along with implications on the vertical structure of latent heating.