Impact of Environmental Aerosols on a Developing Extratropical Cyclone in the Superparameterized Community Atmosphere Model

The impacts of environmental aerosols on the growth of an extratropical cyclone in a realistic winter flow setting are investigated using the superparameterized Community Atmosphere Model (SP-CAM) where cloud-scale dynamics and thermodynamics are explicitly resolved. An examination of the results from 13 ensemble pairs suggests that the growth rate of the cyclone is temporarily reduced as a result of increased aerosol concentrations. A convection–advection–moisture self-adjustment (CAMS) mechanism of aerosol–cyclone interaction is proposed to explain this finding. Specifically, the weakened growth is unambiguously attributed to the weakening of the cold advection underneath the mid-tropospheric trough of the cyclone. The weakened cold advection is in turn driven by a decrease of the zonal temperature gradient that is tied to the reduced latent heating in the stratiform cloud region of the cyclone. Invigoration of convection ahead of the cold front by aerosols is found to be directly responsible for a suppressed moisture supply into the stratiform cloud region and thus the reduced latent heating there. The regional climate implications of these results are discussed. Also highlighted is the importance of incorporating aerosol microphysical effects on deep convection in any modeling effort that aims to understand aerosol–circulation interaction at the extratropics.