Effects of model resolution, physics, and coupling on Southern Hemisphere storm tracks in CESM1.3

Two high-resolution versions of a Coupled Earth System Model (CESM1.3: 0.25 degrees atmosphere, 1 degrees ocean; CESM1.1: 0.25 degrees atmosphere, 0.1 degrees ocean) are compared to the standard resolution CESM1.1 and CESM1.3 (1 degrees atmosphere, 1 degrees ocean). The CESM1.3 versions are documented, and the consequences of model resolution, air-sea coupling, and physics in the atmospheric models are studied with regard to storm tracks in the Southern Hemisphere as represented by 850-hPa eddy kinetic energy. Increasing the resolution from 1 degrees to 0.25 degrees in the atmosphere (same physics) coupled to the 1 degrees ocean intensifies the strength of the storm tracks closer to observations. The 0.25 degrees atmosphere with the older CESM1.1 physics coupled to the 0.1 degrees ocean has fewer low clouds, warmer Southern Ocean sea surface temperatures, a weaker meridional temperature gradient, and a degraded storm track simulation compared to the 0.25 degrees atmosphere with CESM1.3 physics coupled to the 1 degrees ocean. Therefore, deficient physics in the atmospheric model can negate the gains attained by higher resolution in atmosphere and ocean.