NASA Facts: TRMM Instruments
Clouds and the Earth's Radiant Energy System
The Clouds and the Earth's Radiant Energy System (CERES) instrument is one of five
instruments that is being flown aboard the Tropical Rainfall Measuring Mission (TRMM)
observatory. Data from the CERES instrument can be used to study the energy
exchanged between the Sun; the Earth's atmosphere, surface and clouds; and space.
However, it only operated for January-August 1998 and March 2000, so the available
data record is quite brief.
Balancing the Earth's Energy Budget
The Earth's daily weather and climate are controlled by the balance between the amount
of solar energy received by the Earth (both by its surface, and its atmosphere and clouds)
and the amount of energy emitted by the Earth into space. Scientists have been working for
decades to understand this critical energy balance - to understand the budget of incoming
and outgoing energy, called the Earth's radiation budget.
A major portion of the energy received from the Sun is at short wavelengths while the
majority of energy emitted by the surface of the Earth and by clouds is at long wavelengths.
Increases in the amounts of greenhouse gases (gases in the atmosphere that absorb the long
wavelength energy emitted by the Earth) can lead to a warming of the Earth's surface. Such
changes may, in turn, cause changes in the Earth's weather and climate. Some of the
shortwave radiation from the Sun is also reflected back into space by clouds and small
particles in the atmosphere called aerosols. Major sources of aerosols include windblown
dust, emissions from the burning of fossil fuels such as gasoline, and the burning of forests
and agricultural fields biomass burning).
One of the most intriguing questions facing climate modelers today is how clouds affect
the Earth's climate and vice versa. The U.S. Global Change Research Program classifies
understanding the role of clouds and the Earth's energy budget as its highest scientific
priority. Understanding cloud effects requires a detailed knowledge of how clouds absorb
and reflect incoming shortwave solar energy, as well as how they absorb and reemit outgoing
longwave energy. For example, low, thick clouds primarily reflect incoming solar energy back
to space causing cooling. Thin, high clouds, however, primarily trap outgoing longwave
energy and produce warming. To date, satellite studies have found that clouds have an
overall net cooling effect on
Analyses of satellite data also have shown that clouds which form over water are very
different from clouds which form over land. These differences affect the way clouds
reflect sunlight back into space and how much longwave energy emitted by the Earth is
absorbed by clouds and re-emitted. For example, over the equatorial Pacific Ocean during
El Niño events, there is a significant decrease in the amount of energy emitted by the
Earth due to increased cloudiness. El Niño events occur when portions of the Pacific
Ocean become considerably warmer than normal. Clouds appear over the relatively warmer
portions of the eastern Pacific and decrease over the relatively cooler western Pacific.
These changes can affect weather patterns around the world.
Water Vapor Effects
Water vapor in the atmosphere also affects our daily weather and climate, though scientists
are only beginning to understand how this complex mechanism works. Water vapor acts like
a greenhouse gas, absorbing outgoing longwave energy. Because water vapor also condenses
to make clouds, an increase in water vapor in the atmosphere also may increase the amount
The CERES Instrument
The CERES instrument is based on NASA Langley's highly successful Earth Radiation Budget
Experiment which used three satellites to provide global energy budget measurements from
1984 to 1993.
CERES measures the energy at the top of the atmosphere, as well as estimate energy
levels within the atmosphere and at the Earth's surface. Using information from very
high resolution cloud imaging instruments on the same spacecraft, CERES also determines
cloud properties, including cloud amount, altitude, thickness, and the size of the cloud
particles. All of these measurements are critical for advancing our understanding of the
Earth's total climate system
and further improving climate prediction models.
Five CERES instruments have been flown on multiple satellites starting with TRMM, followed
by a launch on the Terra satellite in 1998 and the Aqua
satellite in 2000. Follow-up CERES satellite missions are planned to create a long-term
history of highly accurate energy budget and cloud data for enhanced climate
TRMM is NASA's first mission dedicated to observing and understanding the tropical rainfall
and how this rainfall affects the global climate. It is a joint mission with the Japan Aerospace Exploration Agency. The primary instruments for measuring precipitation are
the Precipitation Radar, the TRMM Microwave Imager, and the Visible and Infrared Scanner.
Additionally, TRMM carries the Lightning Imaging Sensor and CERES. These instruments
can all function individually or in combination with one another. TRMM is part of NASA's
long-term, coordinated research effort to study the Earth as a global system.