Diurnal cycle of rainfall over Lake Victoria Basin during the long-rain season based on TRMM satellite estimate

摘要

The spatial-temporal characteristics of March-April-May rainfall are investigated over Lake Victoria Basin on a diurnal time scale using harmonic and principal component analyses. The study uses high-resolution Tropical Rainfall Measuring Mission 3B42 V7 satellite estimate for the years 1998-2015. The diurnal signal in the initiation time for the land and the lake shows a difference in amplitude and phase with a peak in the late afternoon to evening over the land and late night to early morning over the lake. The rainfall maximum first appears over the highlands on the northeast of the lake around 1500 local standard time (LST) then intensifies and migrates westwards. Around 0300 LST the rainfall is observed ubiquitously over the lake before localizing in the western half of the lake around 1100 LST. There exists an enhanced rainfall amplitude of about 50% of the daily rainfall mean over the northeastern sector of the basin and the western half of the lake. By comparison, the amplitude of the semi-diurnal cycle is weaker and in the range of 1-30% of the daily mean. Rainfall amount (RA) values are higher over the lake and the highlands on the east of the basin while lower on southeastern and western parts of the basin. The distribution of RA, rainfall intensity (RI) and rainfall frequency revealed high peak of RA over the eastern part of the basin that may be attributed to the high incidence of moderate rainfall. The peak over the western half of the lake may be ascribed to the enhanced RI over the lake.