JP1.9
Do Clouds Follow Deforestation Over the Amazon?
Frederic J. F. Chagnon, MIT, Cambridge, MA; and R. L. Bras, J. Wang, E. Williams, A. K. Betts, N. O. Renno, L. A. T. Machado, R. Knox, and G. Bisht
A Bayesian statistical analysis of ten years of remote sensing observations of
cloudiness from geo-stationary satellites (GOES) has produced the strongest
evidence of the impact of land cover over the deforested Amazon on the
development of convective clouds shown by a number of previous studies.
Shallow clouds are prone to appear over deforested surfaces while high clouds
occur over forested surface but much less frequently. A understanding of the
physical mechanisms responsible for the observations was made possible by
using simultaneous measurements of atmospheric sounding at a forest and a
pasture site during the Rondonian Boundary Layer Experiment (RBLE-3). We
demonstrate that the atmospheric boundary layer over the forested area is more
unstable characterized by great values of the convective available potential
energy (CAPE) than over the deforested area. More active shallow convections
over the deforested area than deep convections over the forest was caused by
stronger lifting mechanism mainly due to the mesoscale circulations driven by
deforestation induced surface heterogeneities. We also found that smoke from
biomass burning in the deforested area significantly reduced the formation of
shallow clouds arguably through reducing the drop sizes of cloud water.
Joint Poster Session 1, Land-Atmosphere Interactions
Tuesday, 22 January 2008, 9:45 AM-11:00 AM, Exhibit Hall B
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