A NEW LOOK AT THE DIURNAL-VARIATION OF GLOBAL OCEANIC PRECIPITATION FROM THE OCEAN TOPOGRAPHY EXPERIMENT (TOPEX) AND THE TOPEX MICROWAVE RADIOMETER (TMR)

New results on the diurnal variation of global oceanic precipitation a re obtained by using one year's TOPEX (ocean TOPography EXperiment) an d TMR (TOPEX Microwave Radiometer) data, derived from the dual-frequen cy (K-u and C band) capacity of the altimeter and the non-Sun-synchron ous orbit of the satellite. The diurnal variation is characterized by a three-maximum structure which peaks al 00:00, 08:00, and 16:00 lo ca l time. The midnight-mo mi ng-afternoon maxima and dawn-noon-evening m inima pattern seems to correlate with the results of most previous stu dies and to offer a unified picture of the diurnal variation of oceani c rainfall. A slight daytime (06:00-18:00) preference of oceanic preci pitation appears to be significant in all seasons with the day/night r atio varying from 1.032 to 1.141 and the annual mean being 1.082. Exam ination of the geographical distribution of the timing of diurnal vari ation shows that the majority of the world oceans favour an afternoon maximum and an evening minimum. Moreover, the northern hemisphere is m ore coherent in reaching its maximum, while the southern hemisphere in reaching its minimum. In addition, the mechanisms responsible for the diurnal variations are discussed.