Improved Tropical Variability of Clouds and Precipitation in the E3SM Atmosphere Model with New Physics Parameterizations (Invited Presentation)

Skillfully simulating the observed tropical variability is a longstanding challenge in global atmosphere models; improvements in the variability often lead to degradations in the mean-state climate. Previous versions of the U.S. Department of Energy’s Energy Exascale Earth System Model (E3SM) also struggled to represent these modes of variability. Here, we present simulation results from the latest version of the E3SM Atmosphere Model (EAMv3), with a new microphysics scheme and several enhancements to the deep convective scheme, which significantly improves the variability with minimal impacts on the mean-state clouds and precipitation.

The model improves various modes of convectively-coupled equatorial waves, increasing the strength of Kelvin waves and producing a more coherent eastward propagation of the Madden Julian Oscillation from the Indian Ocean to the central Pacific Ocean. At the same time, the diurnal cycle of precipitation over Tropical land regions is improved. We describe the processes and aspects of the new model physics which lead to these improvements, including an improved representation of convection and the mean-state moisture field around Maritime Continent, and discuss the implications of the improved variability on future simulations.