Environmental & Climate Sciences Department Seminar

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. Two major recent enhancements of Zhang and McFarlane (ZM, 1995) convection parameterization scheme for the version 3 of E3SM:convective mass flux adjustment and convective microphysics parameterization, will be discussed in this presentation. Recent observational studies suggest that the large-scale dynamical forcing (vertical motion) plays important roles in deep convection development. We developed a convective mass flux adjustment approach to represent the dynamical effects of large-scale vertical motion on convection. The coupling of convection with large-scale circulation significantly improves the simulation of climate variability in E3SM across multiple scales from the diurnal cycle, convectively coupled equatorial waves, to the Madden-Julian Oscillation (MJO). Microphysical processes in convective clouds play important roles in aerosol, cloud, circulation, and climate interaction, which can greatly affect cloud precipitation efficiency, latent heating, cloud radiative properties, and thus climate. We developed a two-moment (mass and number concentration), five-class (liquid, ice, rain, snow, and graupel) convective microphysics parameterization and implemented it in the ZM convection scheme in E3SM. This scheme is linked to aerosols through cloud droplet activation and ice nucleation processes, and to stratiform cloud parameterization through convective detrainment of cloud liquid/ice water content and droplet/crystal number concentration, which improves the representation of interactions between aerosols, convective, and stratiform clouds in E3SM. The convective microphysics parameterization also improves the simulation of tropical variability in E3SM.