The analysis of recent high-resolution aircraft observations over the ocean made by radar and passive microwave radiometer reveals significant problems
in relating the brightness temperature measurements of the radiometer with the radar-derived rain rates. A predominant cause of this problem is that the information on rain drops contained in the radiometric measurements is contaminated by
scattering and emission from other hydrometeors present in the field of view (fov) of the radiometer. Extensive observations of rain rate made by ship-borne radars and
by the multichannel Special Sensor Microwave Imager (SSM/I), with a much larger fov, lead to similar conclusions. Considering the variability in the meteorological conditions, and in the hydrometeors spatial distribution, we developed an empirical method to estimate rain rate based on two parameters derived from the SSM/I data, which are related to the convective dynamics. The calibration of this empirical algorithm was performed with radar ground truth for November 1992, available over the TOGA-COARE (Tropical Ocean Global Atmosphere-Coupled Ocean Atmosphere Response Experiment) region. Then the algorithm was applied to the same TOGA-COARE region for the remaining three months available. The comparison between the estimated rain rate and the radar observations gives a correlation coefficient of about 0.85, and the monthly total estimated rainfall has an error of about 13%. This rain retrieval method, tuned for Mesoscale Convective Systems (MCSs), is applicable to the Tropical Rain Measuring Mission (TRMM), where microwave radiometric observations and simultaneous radar observations are
available
