How Does Coupled Tropospheric Chemistry Affect Climate? An Investigation Using the Community Earth System Model Version 2

The depiction of tropospheric chemistry in climate models has greatly improved in recent years. The Community Earth System Model version 2 with Whole Atmosphere Community Climate Model version 6 (CESM2-WACCM6) has implemented fully-coupled tropospheric chemistry with 231 chemical species, an updated aerosol scheme, as well as a fully-coupled ocean. To examine the impacts of these improvements, 100-year preindustrial control simulations were run using the following two configurations 1) a “simplified” CESM2-WACCM6 configuration in which coupled chemistry is confined to the middle atmosphere, and 2) the standard CESM2-WACCM6 configuration with fully-coupled chemistry over all atmospheric levels. Regional differences in surface temperature and the CRE range between -5 K and 5 K and -10 W m-2 to 10 W m-2, respectively. Dynamical changes include an equatorward shift of the mid-latitude jets and weakening of the Southern Hemisphere stratospheric polar vortex. The equatorward shifts of the jets are due to widespread tropospheric cooling.