Diurnal cycle of tropical precipitation in Tropical Rainfall Measuring Mission (TRMM) satellite and ocean buoy rain gauge data

The climatological diurnal cycle of precipitation in the tropics is analyzed using data from rain gauges on ocean buoys and satellite measurements by the Tropical Rainfall Measuring Mission (TRMM) satellite. The ocean buoy data are from the NOAA/Pacific Marine Environmental Laboratory Tropical Atmosphere-Ocean/Triangle Trans-Ocean buoy Network in the tropical Pacific Ocean. TRMM data are from the precipitation radar ( PR) and the TRMM microwave imager (TMI). Climatological hourly mean precipitation rates are analyzed in terms of the diurnal and semidiurnal harmonics. Both data sets confirm an early morning peak in precipitation over ocean regions. The amplitude of the diurnal harmonic over the oceans is typically less than 25% of the mean precipitation rate. Over tropical land masses the rainfall peaks in the afternoon and evening hours. The relative amplitude of the diurnal harmonic over land is larger than over the ocean, often exceeding 50% of the mean rain rate. Previously noted differences between the TMI and PR rainfall retrievals persist in the diurnal cycle. On average the TMI measures more rainfall than the PR and has a larger diurnal variation. Phase differences between the two instruments do not show a consistent bias.