HR: 1340h
AN: A33E-1640    [Abstracts]
TI: Biomass Burning Aerosols Intensify El Nino-Induced Drought in Equatorial Southeast Asia
AU: * Tosca, M G
EM: mtosca@uci.edu
AF: University of California, Irvine, Department of Earth System Science Croul Hall, Irvine, CA 92617, United States
AU: Flanner, M G
EM: mflanner@uci.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307, United States
AU: Zender, C S
EM: zender@uci.edu
AF: University of California, Irvine, Department of Earth System Science Croul Hall, Irvine, CA 92617, United States
AU: Randerson, J T
EM: jranders@uci.edu
AF: University of California, Irvine, Department of Earth System Science Croul Hall, Irvine, CA 92617, United States
AU: Rasch, P J
EM: pjr@ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307, United States
AB: Although the influence of El~Niño on inducing drought in equatorial Southeast Asia is relatively well understood, less is known about feedbacks between El Niño, biomass burning and aerosol forcing in this region Fires associated with El~Niño are a new phenomenon, arising from recent increases in human population and agriculture. We examined the impact of El Niño-induced fire aerosols on regional climate using the Community Climate System Model (CCSM), and the Global Fire Emissions Dataset (GFED) for 1997--2006. In our first experiment, we forced the CCSM and a slab ocean model (SOM) with two single-year emissions datasets, one representing a high fire year (1997) and the other a low fire year (2000). In our second experiment the CCSM, coupled with a data ocean model (DOM) of fixed sea surface temperatures (SSTs), was forced with multi-year emissions, consisting of the 10 year GFED record plus an additional 'buffer' year of 'mean' fire emissions. Climate responses to fire aerosols in the two experiments were determined by analyzing ensembles of forty (SOM) and five (DOM) simulations, respectively.Our results show links between fire, aerosols, and decreases in regional precipitation. The inclusion of fire emissions and their climate effects generally improves agreement between simulations and several satellite datasets, including MODIS, MISR and ISCCP. In the first experiment, fires produce aerosol optical depth (AOD) anomalies of 1.0--1.4 over the areas with the most fire in 1997. In the areas with the highest aerosol concentration, solar absorption by these carbonaceous aerosols increases solar heating rates between the surface and 100 hPa upwards of 0.2--0.3 K day^-1 during the peak fire season (August--October). This intense heating stabilizes the troposphere, suppresses convection, and ultimately decreases precipitation the region. In peak fire season, fire-emitted aerosols reduced precipitation by more than 30% in the areas of highest AOD. This reduces soil moisture by 1--2% nearly uniformly in the region. These results suggest that recent increases in deforestation and fire emissions in equatorial Southeast Asia may intensify El~Niño-induced drought.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0360 Radiation: transmission and scattering
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1640 Remote sensing (1855)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting