Influence of the 2006 Indonesian biomass burning aerosols on tropical dynamics studied with the GEOS-5 AGCM

The direct and semidirect effects of aerosols produced by Indonesian biomass burning (BB) during August-November 2006 on tropical dynamics have been examined using NASA's Goddard Earth Observing System, version 5, (GEOS-5) atmospheric general circulation model (AGCM). Simulations were driven by two sets of aerosol forcing fields calculated offline by a separate aerosol transport model, one that included Indonesian BB aerosol emissions and one that did not. In order to separate the influence of the aerosols from internal model variability, the means of two ten-member ensembles were compared. Diabatic heating from BB aerosols increased temperatures over Indonesia between 150 and 400 hPa. The higher temperatures resulted in strong increases in upward grid-scale vertical motion, which increased water vapor and CO over Indonesia. In October, the largest increases in water vapor were found in the midtroposphere (similar to 25%) while the largest increases in CO occurred just below the tropopause (80 ppbv or similar to 50%). Diabatic heating from the Indonesian BB aerosols caused CO to increase by 9% throughout the tropical tropopause layer in November and 5% in the lower stratosphere in December. The results demonstrate that aerosol heating plays an important role in the transport of BB pollution and troposphere-to-stratosphere transport. Changes in vertical motion and cloudiness induced by aerosol heating can also alter the transport and phase of water vapor in the upper troposphere/lower stratosphere.