EFFECTS OF DEGRADED SENSOR RESOLUTION UPON PASSIVE MICROWAVE PRECIPITATION RETRIEVALS OF TROPICAL RAINFALL

Based on the fundamental relationship involving the interaction of mic rowave radiation with precipitation, microwave-based satellite precipi tation estimates hold the most promise for quantitative rain estimatio n from space. At present, the low-resolution channels onboard the DMSP Special Sensor Microwave Imager (SSM/I) are sampled with a spatial re solution several times larger than the scale at which rainfall is gene rated in typical convective rainbands. Aircraft-based instruments can provide views of the detailed microwave radiometric characteristics of precipitating clouds. In this manuscript, the authors present coincid ent finescale (1-3 km resolution) collocated aircraft radiometric and aircraft precipitation radar measurements collected during the 1993 Tr opical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Exper iment in the western Pacific Ocean. By intentionally degrading the res olution of the aircraft datasets from their native resolution to that of current and future spaceborne sensors, the impact of sensor resolut ion upon a combined radiometer-radar vertical profiling rain-retrieval algorithm (developed and utilized for the Precipitation Intercomparis on Program 2) was examined. Retrieved values of the columnar graupel c ontent were more influenced by the addition of the radar profile than was the columnar rain content. The retrieved values of columnar graupe l were also significantly smaller than previously published results fo r land-based rainfall. The results show that the general trend of the rain structure is maintained but finescale details are lost once the o bservations are reduced to resolutions of 15 km.