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Aerosols that contain black carbon both absorb and reflect incoming
sunlight. Even as these atmospheric particles reduce the amount of
sunlight reaching the surface, they increase the amount of solar energy
absorbed in the atmosphere, thus making it possible to both cool the
surface and warm the atmosphere. The images above show satellite measurements
of the region studied during the Indian Ocean Experiment (INDOEX)—a vast
region spanning the Arabian Sea and Bay of Bengal (west to east), and
from the foot of the Himalayan Mountains, across the Indian subcontinent
to the southern Indian Ocean (north to south).
The 8-day composite image at upper left shows aerosol pollution (brownish
pixels) in the lower atmosphere over the INDOEX study area, as measured
by the Moderate-resolution Imaging Spectroradiometer (MODIS) aboard
Terra. These data were composited from March 14-21, 2001.
The upper right image shows the total solar energy reflected back to space,
as measured by the Clouds and Earth's Radiant Energy System (CERES)
aboard Terra. White pixels show high values, greens are intermediate
values, and blues are low. Note how the aerosols, particularly over the
ocean, increase the amount of energy reflected back to space.
The lower left image shows the absorption of the black carbon aerosols in the
atmosphere. Where the aerosols are most dense, the absorption is
highest. Red pixels indicate the highest levels of absorption, blues are
The lower right image shows that the aerosol particles reduce the amount of
sunlight reaching the surface. Dark pixels show where the aerosols exert
their cooling influence on the surface (or a high magnitude of negative
radiative forcing). The bright pixels show where there is much less
aerosol pollution and the incoming sunlight is relatively unaffected.