A23L-07
Observation-based Estimates of the All-sky Aerosol Direct Radiative Effect and Impact of Uncertainties in Aerosol Properties

Tuesday, 15 December 2015: 15:10
3006 (Moscone West)
David M Winker, NASA Langley Research Center, Hampton, VA, United States, Seiji Kato, NASA Langley Research Ctr, Hampton, VA, United States, Fred G Rose, Science Systems and Applications, Inc. (SSAI), Hampton, VA, United States and Jason Lucas Tackett, Science Systems and Applications, Inc., Lanham, MD, United States
Abstract:
Observation-based estimates of global aerosol direct radiative effects (DRE) have been hampered by satellite aerosol retrievals restricted to clear-sky conditions. Assumptions or model estimates are then required to extend clear-sky estimates to all-sky conditions. Aerosol radiative effects in cloudy skies depend in part on the relative vertical distribution of aerosol and cloud. This represents a major uncertainty in model estimates of aerosol forcing, as the aerosol vertical distribution is poorly constrained and there is a large diversity between models. We have used the CERES-MODIS-CALIPSO-CloudSat (C3M) product to estimate global and regional all-sky aerosol DRE. C3M contains profiles of SW and LW irradiances computed from instantaneous aerosol and cloud profiles from CALIPSO and CloudSat, and collocated MODIS cloud data, all matched to CERES footprints. Aerosol absorption is estimated using a combination of aerosol type information from CALIOP and the MATCH aerosol transport model. Diurnally averaged fluxes are derived and used to estimate annual and seasonal mean DRE.

Global mean all-sky SW TOA DRE is found to be about 2/3 of the clear-sky DRE, due to a combination of cloud-masking of low-altitude aerosol and enhanced warming of absorbing aerosol above cloud. Substantial regional variations in the ratio of all-sky to clear-sky forcing are seen depending on aerosol type and surface albedo. The impact of uncertainties in AOD and aerosol absorption on the estimates of aerosol DRE have been explored by perturbing the aerosol properties used in the radiative calculations. The current level of uncertainty in satellite AOD retrievals is found to contribute significant uncertainty to the aerosol DRE. However, the aerosol DRE is found to be less sensitive to uncertainties in aerosol absorption than in some other recent studies. Details of the approach will be presented, along with a discussion of results.

<< Previous Abstract | Next Abstract >>