In this study the diurnal cycle in rainfall is investigated for the 1997-2001 time period using measurements from self-siphoning rain gauges on ATLAS buoys within the TAO/TRITON and PIRATA moored buoy arrays in the tropical Pacific and Atlantic Oceans. Regional and seasonal differences in the diurnal cycles for seven different climatological regimes are discussed and compared with results from satellite and radar studies.

Results indicate that the seven tropical rain areas defined in this study have a rainfall maximum between midnight and roughly 0800 LT. An additional afternoon maximum is observed at several locations, the most prominent being the northwest Pacific warm pool, the South Pacific Convergence Zone (SPCZ), and the Atlantic ITCZ. The morning maximum in rainfall is found to result from a maximum in both the frequency and intensity of rain events, while the afternoon maximum results mainly from a maximum in the intensity of events. However, these results are not generally applicable to all regimes or seasons, as will be shown.