Rain retrieval method for mesoscale convective systems

The analysis of recent high-resolution aircraft observations over the ocean made by radar and passive microwave radiometer reveals significant problem s in relating the brightness temperature measurements of the radiometer wit h 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 Micro wave Imager (SSM/I), with a much larger fov, lead to similar conclusions. C onsidering the variability in the meteorological conditions, and in the hyd rometeors spatial distribution, we developed an empirical method to estimat e rain rate based on two parameters derived from the SSM/I data, which are related to the convective dynamics. The calibration of this empirical algor ithm was performed with radar ground truth for November 1992, available ove r the TOGA-COARE (Tropical Ocean Global Atmosphere-Coupled Ocean Atmosphere Response Experiment) region. Then the algorithm was applied to the same TO GA-COARE region for the remaining three months available. The comparison be tween the estimated rain rate and the radar observations gives a correlatio n coefficient of about 0.85, and the monthly total estimated rainfall has a n error of about 13%. This rain retrieval method, tuned for Mesoscale Conve ctive Systems (MCSs), is applicable to the Tropical Rain Measuring Mission (TRMM), where microwave radiometric observations and simultaneous radar obs ervations are available.