Carbonaceous aerosol transport and radiative forcing estimates in LMD-Z GCM
Abstract
Simulation of the distribution of global carbonaceous aerosols and their direct radiative forcing were carried out using the Laboratoire de Météorologie Dynamique General Circulation Model (LMD-Z GCM). The global black carbon (BC) and organic carbon (OC) emissions for fossil fuels and biomass sources were included. The emissions from open biomass burning (forest fires and field crop waste burning) sources were dynamical in nature, and were generated using monthly inter-annual satellite fire counts. The natural sources of OC were included assuming a constant fraction (5%) of monoterpene conversion to OC. To estimate the aerosol optical depth (AOD) and radiative forcing, different optical properties were calculated accounting for the effect of hygroscopic growth. The simulations were carried out in a nudged mode, using the ECMWF meteorological data, for a three year period, between 1997 and 1999, after allowing 3 months of spin up period. The model is validated by comparing predicted concentrations with measurements in different geographical locations over the globe. The seasonal trends of BC and OC are compared using data from the IMPROVE network at various locations in the United States. Detailed validation over European and Asian continental sites, and remote locations, were also carried. The measured seasonal cycle is well reproduced by the model and concentrations are within a factor of two of the measured values. To understand the accuracy of the seasonality of the biomass sources and transport pattern in Africa and South America, carbonaceous aerosol optical depth during burning season is compared with AERONET stations AOD. The predicted AODs compare well with measured AODs with good representation of the seasonal biomass burning. There is an improvement in the model performance when using the dynamical open biomass burning emissions instead of the standard emission inventory. The globally averaged AOD at 550 nm is 0.0155, with 0.0186, and 0.0128 for Northern and Southern Hemisphere, respectively. The regional differences in the carbonaceous aerosol concentrations and optical depths arising from source configurations, and transport regimes will be discussed. An estimate of the carbonaceous aerosol direct radiative forcing will be presented, and implications for the regional and global climate change are discussed in the paper.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....8737S