Diurnal cycle of precipitation in a global cloud-resolving model

This study summarizes the diurnal cycle of precipitation that is simulated by a global cloud resolving model (GCRM) named NICAM (Nonhydrostatic ICosahedral Atmospheric Model) which does not use cumulus parameterizations due to high horizontal resolution. Thirty-day integration by NICAM successfully simulates precipitation diurnal cycle associated with land/sea breeze and thermally-induced topographic circulations as well as the horizontal propagation of diurnal cycle signals. A first harmonic of the diurnal cycle of precipitation in 7 km-mesh run agrees very well with the satellite observations in its geographical distributions although the amplitude is slightly overestimated and peak time is 1.5 hour later than that observed over land. Sensitivity experiments, changing the horizontal resolution, suggest that prominent resolution dependence is discernible in the precipitation diurnal cycle in NICAM. The coarser resolution (14 km mesh) run induces about three hour later peak than that in 7 km mesh run. The 3.5 km mesh run realistically produces peak time (around 15 LT) and amplitude similar to those observed in TRMM PR observations. Meanwhile, the resolution dependences in phase and amplitude are negligibly small over ocean domains. The different sensitivity against the horizontal resolution attributes to the different structures and life cycles of convective systems between land and ocean. The NICAM simulation revealed that the diurnal cycle of rainfall over the maritime continent is strongly coupled with the land-sea breeze systems controlling a convergence/divergence pattern in the lower troposphere around the islands. Additionally, the analysis on the cold pool events suggests that the cold pool is often formed over the open ocean where the precipitation intensity is high, and cold pool propagation is related to the diurnal cycle of precipitation as well as the land-sea breeze.