Global three-dimensional simulation of multi-component aerosol transport and radiative forcing with GCM
Abstract
In this paper we present estimates of aerosol distributions and optical depths (AOD) for major atmospheric aerosol species including sulfate, black carbon (BC), organic carbon (OC), mineral dust and sea salt (SS) computed in the Laboratoire de Météorologie Dynamique General Circulation Model (LMD-Z GCM). The LMD-GCM includes all major anthropogenic and natural sources for the above aerosol species. Open biomass burning emissions include seasonal to inter-annual variability using the satellite measured fire counts, wind dependent sea-salt emissions, and dust emission algorithm that quantifies dust source as function of soil mineralogical composition. The natural sources of OC were included assuming a constant fraction (5%) of monoterpene conversion to OC. To calculate optical depth and radiative forcing, different optical properties were calculated accounting for hygroscopic growth and change in refractive indices, for organic carbon, sulfate, and sea salt. The simulations were carried out in a nudged mode, using the ECMWF wind fields for the three year period of 1996 and 1998, after allowing 3 months of spin off period. The model performance is validated by comparing predicted AODs with sun photometer AERONET measurements at different parts of the globe. The model reproduces the seasonal variations at most of the sites, especially at places where biomass-burning aerosols dominate. There are large geographical and seasonal variations of calculated AOD, controlled mainly by emission, transport, and hygroscopic properties of aerosols. The model estimates of AODs at 500 nm compare well with satellite retrieval products from POLDER over ocean. The model reproduces most of the prominent features in satellite data, with an overall agreement within a factor of 2 over the aerosol source areas and outflow regions. The globally averaged AOD at 500 nm is 0.19, with relative contributions of sulfate, BC, OC, dust and sea salt of 26%, 2%, 28%, 18% and 26%, respectively. The relative importance of different aerosol species over different geographical regions will be discussed in the context of possible regional climate effects. An assessment of the direct radiative forcing from multi-component aerosols will also be presented.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....8976S