Assessment of the Aerosol and its Radiative Forcing Simulated from the GEOS-Chem-APM with Remote Sensing Data

Abstract:

Recent AeroCom phase II experiments showed a large diversity in aerosol optical depth (AOD) among 16 detailed global aerosol models, which contributes to the large uncertainty in the predicted aerosol radiative forcing. The GEOS-Chem-APM, a global size-resolved aerosol model, can be considered as a representative AeroCom II model. In this study, multi-year AOD data (2004-2012) from ground-based remote sensing data AERONET as well as satellite retrievals MODIS, MISR and SeaWiFS are used to evaluate the performance of the GEOS-Chem-APM in capturing observed seasonal and spatial AOD variations. By incorporating a radiation transfer model, we then derive the anthropogenic aerosol radiative forcing, and examine the dependencies of the radiative forcing on different affecting factors. We also investigate the anthropogenic contribution to cloud condensation nuclei (CCN) and associated first aerosol indirect radiative forcing using online aerosol–cloud–radiation calculation.

The aerosol direct and indirect radiative forcings derived from global modeling also differ substantially with satellite-based calculations. Therefore, we assess satellite-based direct radiative forcing and indirect radiative forcing by employing the cloud product from CERES SSF and AOD product from MODIS in combination with the fraction of anthropogenic aerosol optical depth obtained from model simulations using the GEOS-Chem-APM. A statistical relationship between planetary albedo and cloud properties, and, further, between the cloud properties and column aerosol concentration, which is required for the estimations, is derived from satellite retrievals. The uncertainties of both model simulations and satellite-based estimations are analyzed and comparisons in aerosol radiative forcing between simulations and satellite-based estimations are presented.