PNNL

Abstract

The representation of convection in global climate models is one of the most challenging scientific issues in climate modeling. Many deficiencies in precipitation and climate variability simulations and uncertainties in climate change projections can be traced to the poor representation of convection. Recent observational studies suggest that large-scale vertical motion plays important roles in deep convection development. In this study we propose a convective mass flux adjustment (MAdj) approach to represent the effects of large-scale vertical motion on convection in the Department of Energy’s Energy Exascale Earth System Model version 2 (E3SMv2). With MAdj, convection is enhanced (suppressed) when there is large-scale ascending (descending) motion at the planetary boundary layer top. The coupling of convection with large-scale circulation significantly improves the climate variability simulation of E3SMv2 across multiple scales from the diurnal cycle, convectively coupled equatorial waves, to the Madden-Julian Oscillation. Improving climate variability simulation through modifying convection parameterization usually causes degradations of the mean state and other climate aspects. The MAdj approach does not degrade the climatology simulations. It actually slightly improves the climatology simulations in precipitation, cloud, radiation, circulation, temperature and moisture fields.