ADDRESSING CLIMATE MODEL BIAS OVER CONTINENTS: ROLE OF OROGENIC ORGANIZED PROPAGATING CONVECTION

Abstract:

Global climate models commonly feature severe warm and dry bias over continents. We address this issue for the United States warm season via high-resolution simulations, continental-scale radar observations, and dynamical analogs. The bias is argued to stem from the absence in climate models of orogenic propagating convective systems that provide over 50% of warm-season rainfall because: i) convective parameterizations fail to represent key dynamical processes; ii) climate model spatial resolution does not permit explicit organized convection. Particularly important are mesoscale downdrafts (Earth’s natural air-conditioners) that, on regional scales, bring air of lower thermodynamic energy above the boundary layer to the land surface. On a broader note, organized convection is central to the water-cycle, diurnal-cycle, energy and momentum fluxes, hydrology, and albedo, all of which affect the distribution and variability of surface temperature and moisture.