Diurnal cycles of precipitation in observations and GCM simulations

Simulations by a global climate model (GCM) of the diurnal cycle of precipitation in the tropics are compared with satellite observations from the Tropical Rainfall Measuring Mission (TRMM) satellite. Over the tropical Pacific and Atlantic Oceans the TRMM data are validated by comparing the climatological diurnal cycle of precipitation with data from rain gauges on the NOAA/PMEL TAO/TRITON/PIRATA buoy networks. 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 semi-diurnal 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 peak occurs in the afternoon and evening hours. The relative amplitude of the diurnal harmonic over land is larger than over ocean, often exceeding 50% of the mean rain rate. The satellite results are compared with simulations of tropical precipitation in the NCAR Community Atmosphere Model (CAM). Differences between the amplitude and phase of the diurnal cycle in the model and in observations are discussed.