Separation of convective and stratiform precipitation using microwave brightness temperature

This paper presents a new scheme that classifies convective and stratiform (CIS) precipitation areas over oceans using microwave brightness temperatur e. In this scheme, data are first screened to eliminate nonraining pixels. For raining pixels, C/S indices are computed from brightness temperatures a nd their variability for emission (19 and 37 GHz) and scattering (85 GHz). Since lower-resolution satellite data generally contain mixtures of convect ive and stratiform precipitation, a probability matching method is employed to relate the CIS index to a convective fraction of precipitation area. The scheme has been applied on synthetic data generated from a dynamical cl oud model and radiative transfer computations to simulate the frequencies a nd resolutions of the Tropical Rainfall Measuring Mission (TRMM) Microwave (TMI) Imager as well as the Special Sensor Microwave/Imager (SSM/I). The re sults from simulated TMI data during the Tropical Ocean Global Atmosphere C oupled Ocean-Atmosphere Response Experiment agree very well with the ground -based radar classification maps; The classification accuracy degrades when SSM/I data is used, due largely to the lower spatial resolution of the SSM /I. The successful launch of TRMM satellite in November 1997 has made it possib le to test this scheme on actual TMI data. Preliminary results of TMI deriv ed CIS classification compared with that from the first spaceborne precipit ation radar has shown a very good agreement. Further verification and impro vement of this scheme are under way.