2002 Annual

Thursday, 17 January 2002: 8:30 AM
Biosphere-Atmosphere Interactions in Amazonia
Carlos A. Nobre, Brazilian Weather and Climate Forecasting Center, Cachoeira Paulista, Brazil
The Amazon Basin contains the largest, contiguous extent of tropical forest on Earth, almost 5.8 million km2. Over the past 30 years almost 600,000 km2 have been deforested in Brazil alone due to the rapid development of Amazonia. Field studies carried out over the last 20 years clearly showed local changes in the water, energy, carbon, and nutrient cycling, and in the atmospheric composition caused by deforestation and biomass burning. There are also some observational evidences of sub-regional changes in surface energy budget and boundary layer cloudiness and regional changes in the lower troposphere radiative transfer due to biomass burning aerosol loadings. There is strong reduction of solar radiation at the surface in excess of 30 W/m2 over several months during the dry season due to aerosol absorption and scattering. At the surface, a small amount of cooling is observed. Throughout the boundary layer black carbon absorbs solar radiation and heats up the atmosphere. That may have implications to the stability of the boundary layer. Larger number of CCN due to biomass burning has led to the speculation of their possible role in cloud formation and rainfall. During the rainy season, in contrast, there are very few amounts of CCN of biogenic origin and the Amazonian clouds show characteristics of oceanic clouds. On the other hand, carbon cycle studies of the Large Scale Biosphere-Atmosphere Experiment (LBA) indicate that the undisturbed forest may be a strong sink of carbon at rates from 1 to 7 ton C/ha/year. Deforestation and biomass burning represent net carbon dioxide emissions of about 0.2 Gton C/year. However, it is still uncertain whether the forest functions as a sink or source of carbon to the atmosphere. The LBA Experiment is producing new knowledge on the physical, chemical and biological functioning of Amazonia, its role for our planet and the impacts in that functioning due to changes in climate and land use.

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