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Ann. Geophys., 20, 2105-2109, 2002
www.ann-geophys.net/20/2105/2002/
© European Geosciences Union 2002
Letter to the Editor
Aerosol radiative forcing over land: effect of surface and cloud reflection
S. K. Satheesh
Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore – 560 012, India
Correspondence to: S. K. Satheesh
(satheesh@caos.iisc.ernet.in)
Abstract. It is now clearly
understood that atmospheric aerosols have a significant impact on climate due
to their important role in modifying the incoming solar and outgoing infrared
radiation. The question of whether aerosol cools (negative forcing) or warms
(positive forcing) the planet depends on the relative dominance of absorbing
aerosols. Recent investigations over the tropical Indian Ocean have shown that,
irrespective of the comparatively small percentage contribution in optical
depth ( ~ 11%), soot has an important role in the overall radiative forcing.
However, when the amount of absorbing aerosols such as soot are significant,
aerosol optical depth and chemical composition are not the only determinants of
aerosol climate effects, but the altitude of the aerosol layer and the altitude
and type of clouds are also important. In this paper, the aerosol forcing in
the presence of clouds and the effect of different surface types (ocean, soil,
vegetation, and different combinations of soil and vegetation) are examined
based on model simulations, demonstrating that aerosol forcing changes sign
from negative (cooling) to positive (warming) when reflection from below
(either due to land or clouds) is high.
Key words. Atmospheric composition
and structure (aerosols and particles) History of Geophysics (atmospheric
sciences) Hydrology (anthropogenic effects)
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