A new global rainfall rate model

A new global rainfall rate model has been developed for improving the accuracy of rain attenuation prediction in Earth-satellite and terrestrial links. The required meteorological parameters are the annual rainfall amount (mm), the probability of rainy 6 hour periods and the portion of convective-type rains from all rains. They have been calculated from the 6 hour rainfall forecasts of the European Centre for Medium-range Weather Forecasts (ECMWF) from October 1992 to September 1994. The accuracy of the two first parameters have been improved using also the precipitation data of the Global Precipitation Climate Project (GPCP) from 1986 to 1992. The new method was validated against rainfall rate data from about 60 sites including about 140 experiment years. The mean RMS-value of the relative differences between predicted and measured rainfall rates for time percentage range from 0.001 to 1% is about 28%, when ECMWF data together with GPCP-data has been used, and about 32%, when only the global ECMWF-data has been used. The corresponding difference between ITU-R rain zones and measured rainfall rates is about 39%. Further improvements could be obtained using more long-term data from the ECMWF rainfall forecasts than two years