Impact of Horizontal Spatial Resolution on Simulated Aerosol Distributions and Radiative Forcing in the NASA GEOS-5 Earth System Model

The NASA Goddard Earth Observing System, version 5 (GEOS-5), is a global Earth system model that includes a representation of the lifecycle of atmospheric aerosols through the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART) module. GOCART includes sources, chemistry, and sinks of major tropospheric aerosol species, including dust, sea salt, sulfate, and black and organic carbon. The aerosols in GOCART are radiatively coupled to the atmosphere and are available for coupling to other Earth system components (e.g., atmospheric chemistry, moist physics, ocean biogeochemistry). GEOS-5 can be run in various horizontal spatial resolutions, typically from a coarse ~200 km spatial resolution used for long-time integration chemistry-climate simulations to a ~25 km spatial resolution used in the current near-real time forecasting system. Even higher spatial resolutions have been run, and the target for the next version of the near-real time system is a global 12.5 km resolution. We explore the impact of varying the model horizontal spatial resolution on the simulation of aerosol distributions in GEOS-5. Specific foci include the impact of spatial resolution on the surface wind fields used to drive dust and sea salt emissions, on the representation of moist physics processes which impact aerosol wet removal and aqueous chemistry, and on the resulting radiative forcing. Two configurations of the GEOS-5 system are used, one which is run in an AMIP-style climate mode and another which is driven by assimilated meteorology in a data assimilation-like mode.