Diurnal Variation of Precipitation over the Tropical Oceans Observed by TRMM/TMI Combined with SSM/I

Abstract

The Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) data are used in this study as the first passive microwave information from a precessing orbit to reveal diurnal variations of precipitation over the tropical oceans (30°S–30°N). Data from three Special Sensor Microwave Imagers are combined to help alleviate the aliasing problem caused by the slow diurnal sampling of the TRMM satellite. Annual mean diurnal variations of rainfall in 1998 are presented for 10° latitude bands and six regions. The diurnal variation over all the tropical oceans exhibits an amplitude of about ±14% of the mean, and it peaks near dawn (approximately 0400–0700 LST). By latitude band, diurnal variation is most evident in the deep Tropics, while the ratio of the amplitude over the mean is relatively constant over most latitude bands. Other than in the early morning, there are no evident peaks exceeding the error bars for this analysis. By region, the coastal areas where the ITCZ intersects large continents and around the Maritime Continent are dominant. The morning preference of rainfall prevails almost everywhere in the open ocean where the mean rainfall is heavy, even though the amplitude is small compared to that near the continents.