An equilibrium cloud-resolving modeling study of diurnal variation of tropical rainfall

•Rain intensity does not show any diurnal signals.•Fractional rainfall coverage has a diurnal cycle.•FAC is sensitive to rainfall but it is insensitivity to change in rain intensity.•The diurnal cycle of fractional rainfall coverage corresponds to that of IR cooling.

The diurnal variation of tropical rainfall is examined through the analysis of an equilibrium cloud-resolving model experiment. Model domain mean rain rate is defined as a product of rain intensity and fractional rainfall coverage. The diurnal variation of the mean rain rate is associated with that of fractional rainfall coverage because the diurnal variation of rain intensity is significantly weakened through the decrease in rainfall in early morning hours. The decrease in rainfall corresponds to the reduction in secondary circulations through the barotropic conversion from the perturbation kinetic energy to the mean kinetic energy under the imposed negative vertical gradient of westerly winds. The fractional rainfall coverage shows the diurnal signal with the maximum in the early morning hours primarily due to nocturnal infrared radiative cooling.