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introduction /
modis /
misr /
aster /
mopitt /
ceres /
conclusion
| CERES, Bruce Barkstrom |
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The only way the Earth receives the energy that keeps the surface
warm is through sunlight. Some of the incoming sunlight is
reflected back up into space by the Earth's surface, atmosphere,
and clouds; some of it is absorbed and stored as heat. When the
surface and atmosphere warm, they emit heat, or thermal energy, to
space. The "radiation budget" is an accounting of these energy
flows. If the radiation budget is in balance, then, the surface of the
Earth should be neither warming nor cooling, on average. |
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The CERES, or Clouds and the Earth's Radiant Energy System,
instrument measures reflected sunlight. In this image, the dark and
unreflective ocean is colored blue, while the more reflective land is
colored green to grey. Clouds are very reflective. We see them
standing out from the dark ocean. |
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CERES measures the energy emitted by the surface and atmosphere
of the Earth. This image shows high emission from warm surfaces
in yellow. Where the surface is colder, the image appears blue or
white. Over the Sahara, we see through to the very warm surface
of the Earth. Nearer the poles, clouds cover the surface and we see
them as cold, blue areas in this image. |
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The excess sunlight warms the Tropics. If ths continued
over a long time, the Tropics would just keep warming. The Polar
regions receive less energy from the sun than they emit to space,
and so they cool. The temperature difference between the Tropics
and the Poles creates winds and ocean currents that carry excess
heat and moisture. When the moisture encounters cooler temp-
eratures as it moves to the poles, clouds form and reduce the
emission of energy to space. This animation shows the weather
systems driven by the distribution of energy measured by CERES.
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Clouds play a complex role in the Earth's radiation budget. Low
Clouds reflect much of the sunlight that falls on them, but have little
Effect on the emitted energy. Thus, low clouds act to cool the
Current climate. High clouds reflect less energy, but trap more of
The energy emitted by the surface. About 10 years ago, measure-
Ments like those of CERES showed that clouds act to cool the
current climate. However, the measurements could not tell us why
the clouds in different parts of the Earth were different from one
another. CERES cannot answer this question by itself; the other
instruments on Terra will make contributions to what CERES
measures that will improve our understanding of why clouds act
the way they do in the current climate, and what we may expect
them to do in the future.
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Scientists assessing our understanding of climate have looked at
many mechanisms that might change climate: volcanoes, green-house gas changes, aerosols, the properties of the Earth's surface.
This chart illustrates our current understanding of the relative
importance of these various kinds of climate forcing mechanisms.
The uncertainty in what clouds will do in the future remains the
largest source of uncertainty in predicting the future climate.
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This picture shows one of the educational outreach activities that
Terra includes: the CERES S'COOL Project, short for Student
Cloud Observations On-Line. When the CERES instruments on
Terra pass over the schools, the students in S'COOL observe the
Clouds and send in their observations to the S'COOL Project at
NASA's Langley Research Center. About 500 schools are
Currently participating in this international program.
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introduction /
modis /
misr /
aster /
mopitt /
ceres /
conclusion
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