Simulating aerosol-radiation effect on subseasonal prediction in a coupled Unified Forecast System and CCPP-Chem: prescribed aerosol climatology versus dynamic aerosol model

This study examines the impact of aerosol-radiation interation on subseasonal prediction using the Unified Forecast System (UFS) coupled to an ocean and an aerosol component. The aerosol component is from the current NOAA operational GEFS-Aerosols model, which includes the GOCART aerosol modules, simulating sulfate, dust, black carbon, organic carbon, and sea-salt aerosols. The modeled aerosol optical depth (AOD) is compared to reanalysis from Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA2) and observations from Moderate Resolution Imaging Spectro-radiometer (MODIS) satellite. Despite AOD bias primarily in dust and sea salt, good AOD agreement is achieved. The simulated radiative forcing (RF) from the total aerosol at the top of the atmosphere is approximately -2.5 W/m2 or -16 W/m2 per unit AOD globally. This is consistent with previous studies.

In parallel simulations, the dynamic prognostic aerosols are replaced with modeled climatological aerosol concentrations in the UFS. While regional differences in RF are noticeable in some special events between these twin experiments, the resulting RF, surface temperature, precipitation and geopotential height at 500 hPa, show similarity over multi-years in subseasonal applications. This suggests that replacing the costly chemistry module with the modeled aerosol concentration climatology is a possible alternative in the subseasonal applications.