Diurnal cycle of precipitation and atmospheric humidity flux in South America: role of land-atmosphere interactions

GILES, JULIÁN; R. C. RUSCICA; C.G. MENÉNDEZ

Beijing

Conferencia; The International Conference on Regional Climate CORDEX 2019; 2019

WCRP/CORDEX

Model accuracy of the timing of precipitation in its diurnal cycle is as important as that of the daily mean to correctly represent climate, but nevertheless it is often overlooked. We analyzed the diurnal cycles of precipitation (DCP) and convergence of atmospheric humidity over South America in the wet season (October through March), using two regional climate models (RCA4 and LMDZ). The simulations were compared with two satellite-derived products and one reanalysis. Consistent with previous results, these RCMs have a wrong representation of the DCP because precipitation is being unrealistically triggered too easily. Both models showed qualitatively similar errors in the DCP compared to reference data. However, the humidity flux convergence - a necessary condition for a correct rainfall simulation - and its diurnal cycle at the continental scale were satisfactorily captured compared to the reanalysis. We speculate that the boundary layer evolution and its thermodynamic properties could be sensitive to the coupling between the soil and the atmosphere. In order to explore if the diurnal cycles of convection and different properties of the boundary layer are sensitive to the land-atmosphere coupling, an additional run was performed with each RCM: an Uncoupled experiment that shares the same set-up as the control (coupled) one, except that its soil-moisture evolution at each day is replaced with the climatology of the control for that day, uncoupling the land surface from the atmosphere. The main results of this experiment will be presented during the conference.