Impacts of model resolution and physics on the diurnal rainfall cycle over tropical lands

Monday, 15 December 2014
Yi-Chi Wang, Research Center for Environmental Changes Academia Sinica, Taipei, Taiwan
Diurnal cycle of rainfall is especially important as it manifests interactions between atmosphere, land, and ocean. However, biases of diurnal rainfall cycle such as too early-onset of land convection, lack of nocturnal rainfall, and lack of propagating diurnal convective organization near the topographical regions, are often found in climate models. These biases have been attributed to deficiencies of cumulus parameterization and/or insufficiencies of model resolution to represent important processes on the diurnal scale in the previous studies.

This study focuses on the impacts of resolution and deep cumulus schemes on diurnal rainfall cycle simulated by Community Atmosphere Model version 5.0. Processes on the diurnal scale simulated by CAM is validated with TRMM observations and ERA-Interim reanalysis. Early onset of convection and lack of nocturnal rainfall are both noticed in model simulations over tropical lands. These biases are found to be mostly attributed to the triggering function of deep cumulus scheme, not to the model resolutions, whereas finer model resolution contributes to improvements over topographical regions. Interaction of rainfall and large-scale circulation on the diurnal scale are investigated with the transpose AMIP setup during YOTC period.