Influences of biomass burning on land-atmosphere interactions and dry-to-wet transition over Amazonia

HR: 1340h
AN: A23C-0818 [Abstracts]
TI: Influences of biomass burning on land-atmosphere interactions and dry-to-wet transition over Amazonia
AU: * Zhang, Y
EM: yzhang@eas.gatech.edu
AF: School of Earth & Atmospheric Science,Georgia Tech, 311 Ferst Dr., Atlanta, GA 30332
AU: Yu, H
EM: hyu@eas.gatech.edu
AF: School of Earth & Atmospheric Science,Georgia Tech, 311 Ferst Dr., Atlanta, GA 30332
AU: Fu, R
EM: fu@eas.gatech.edu
AF: School of Earth & Atmospheric Science,Georgia Tech, 311 Ferst Dr., Atlanta, GA 30332
AB: Observations have demonstrated that the dry-to-wet transition in Amazon basin is sensitive to small changes of the atmospheric thermodynamic conditions. It is thus reasonable to hypothesize that the wet-season onset can be influenced by smoke aerosols produced by the large-scale biomass burning. To test this hypothesis, a regional climate model (RegCM3) is forced with MODIS-retrieved aerosol optical depth in combination with GOCART simulations of aerosols during the dry-to-wet transition season (August-November). We examine the direct and semi-direct effects of smoke on the transition season. Our results show that the reduction of the solar flux is mainly responded by reduction of surface sensible flux. This consequently reduced the diurnal growth of the atmospheric boundary layer (ABL), and detrainment of dry air at the top of the ABL. The cloud formation is inhibited due to strong aerosol absorption. Such semi-direct effect can compensate the direct effect of aerosols on moist static instability and thus rainfall.We also found that these changes are sensitive to the prescribed vertical distribution of the aerosols. The simulations are also compared with MODIS aerosol-cloud and radiosonde measurement in 2002. The physical and dynamic processes key to determine the aerosols_ influence on wet season onset will be discussed.
DE: 9360 South America
DE: 3322 Land/atmosphere interactions
DE: 3359 Radiative processes
DE: 4801 Aerosols (0305)
DE: 1704 Atmospheric sciences
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting