A summary of reflectivity profiles from the first year of TRMM radar data

A preliminary climatology of reflectivity profiles derived from the first s paceborne precipitation radar (PR), which is on board the Tropical Rainfall Measuring Mission (TRMM) satellite, is described using the data from Janua ry 1998 to February 1999. This study focuses on the behavior of the melting -layer (bright band) altitude in stratiform precipitation. This analysis wi ll be useful for improving passive microwave radiometric estimations of rai n rates because it provides information about otherwise unknown parameters in the estimation models (the depth of the rain column). The monthly means of the melting-layer altitude estimated over 10 degrees x 10 degrees latitu de-longitude grid boxes show that high melting layers (>4.5 km) tend to app ear during extreme events such as El Nino and the Asian summer monsoon, and lower melting layers are usually observed in the winter hemisphere, which suggests a close relationship between surface temperature and the melting-l ayer altitude. Detailed climatologies of the profiles are provided for eigh t selected regions. For each region the seasonal variation of the meting-la yer altitude and the mean and variation of the reflectivity profiles are di scussed. The diurnal cycle of the melting-layer altitude and second-moment products, such as the spatial correlation along the satellite track, illust rate the irregular characteristics of the melting-layer altitude.