ABSTRACT


                 Research over the past decade has confirmed and
highlighted the importance of a number of aerosol effects on climate, both
through direct interaction of the aerosol with solar and terrestrial
radiation, and via perturbations of cloud properties and convective
dynamics. In this presentation, I will highlight recent results from a
study of the effect of biomass smoke on tropical clouds and the
consequences for regional and global climate. We investigated the emission
of smoke from biomass burning, its regional distribution, and its effects
on cloud microphysics during the LBA-SMOCC experiment in Amazonia,
September-October 2002. The campaign consisted of airborne, ground-based,
remote-sensing, and modeling components. Two instrumented aircraft
investigated trace gases, aerosol properties and cloud microphysics across
a large region that comprised highly polluted and essentially pristine
airmasses. At a ground site, we made continuous measurements of trace gases
and a large suite of aerosol properties, and collected samples for
laboratory analysis. Measurements spanned from the peak of the burning
season, with high smoke concentrations, to fairly clean conditions in the
early rainy season.

We found high loadings of smoke particles and pyrogenic trace gases in the
boundary layer over vast reaches of Amazonia, and evidence for efficient
vertical transport of smoke into the free troposphere. Smoke aerosols had
pronounced effects on the radiation budget, cloud microphysics and
precipitation formation over Amazonia, as show by in-situ measurements and
remote sensing data. These effects are likely to perturb convective
dynamics, radiative flux, and atmospheric composition on regional to global
scales.

With the increase in knowledge about aerosol effects on climate, the
uncertainty about the magnitude of aerosol-driven climate forcing has
increased dramatically over the past decade. This has very serious
consequences for our ability to assess the sensitivity of the climate
system to anthropogenic forcing, and casts a discomforting shadow over the
climate change scenario for the upcoming decades.



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