The beginning of summer is an annual reminder that our world is driven by sunlight, and new Terra satellite measurements show just how much the Sun influences the Earth's climate system.

The first observations, from March 2000 to May 2001, of the Clouds and the Earth's Radiant Energy System (CERES) instruments aboard Terra are the most accurate global radiation or energy measurements ever and include the first complete year of such essential data since 1987. These new CERES data, available at NASA Langley Research Center's Atmospheric Sciences Data Center, Hampton, VA, capture incoming and outgoing energy over the whole planet and provide new insights into climate change.

What do the colors mean? The lowest amount of sunlight reflected back to space, shown in blue, occurs over clear ocean areas. Green colors show gradually increasing amounts of reflected sunlight. The areas of greatest reflected solar energy, shown in white, occur both from the tops of thick clouds and from ice-covered regions on the Earth's surface during summer. Photo: NASA

"The new data will play a critical role in narrowing the uncertainties in predictions of future climate change, especially for the undefined role of the Earth's cloudiness," said Bruce Wielicki, a CERES principal investigator at Langley, where the CERES mission is managed.

For scientists to understand climate, they must also determine what drives the changes within the Earth's radiation balance. CERES measured some of these changes over the last year, producing new images that represent data collected twice per day over the whole planet. CERES captured the May 2001 heat wave that swept across the southwestern United States. Temperatures soared to as high as 109 F in parts of California, setting new records.

The recent U.S. heat wave is only one example of outgoing energy from the Earth. Everything, from an individual person to the Earth as a whole, emits energy. As Earth absorbs solar energy, it warms up. To keep our planet at an overall hospitable temperature, the Earth must emit some of this warmth, or energy, into space.

Record setting U.S. heat wave: CERES measured thermal radiation or heat emitted from the United States, as shown in this image from May 2001. The record-setting high temperatures experienced in Southern California and Nevada on May 9 are visible in the yellow areas where great amounts of thermal energy are escaping to space. The levels of energy increase from blue to red to yellow. This example illustrates one of the most basic stablizing forces in the Earth's climate system: clear hot regions lose more energy to space than cold areas. The blue regions of low thermal emission over the northern U.S. are cold cloud tops. Photo: NASA

Earth's outgoing energy has two components: thermal radiation emitted by the Earth's surface and atmosphere, as in last month's heat wave, and solar radiation reflected back to deep space by the oceans, lands, aerosols and clouds.

It is the balance, which scientists refer to as the Earth's "radiation budget," between the incoming energy from the Sun and outgoing energy back to space that determines Earth's temperature and climate. This balance is controlled by both natural and human-induced changes, giving scientists a wide range of questions to study.

Even though CERES has the ability to capture short-term changes like the recent heat wave, "the real power of the CERES data will come from the analysis that integrates CERES' highly accurate measurement of energy with other measurements from Terra of the individual components of the climate system," Wielicki said.

The international CERES team is now completing an integration of satellite data over the entire planet from space-borne instruments on seven different spacecraft to test the accuracy of global climate models, a task never before attempted. This will allow a new picture of the energy balance from the top of the atmosphere, all the way down to the surface of the Earth. Analyzing how well climate models compare to CERES will tell the researchers which areas most closely illustrate the Earth's natural responses.

Deadly May heat wave in Pakistan: CERES also measured the thermal energy emitted from the regions of the Indian subcontinent and northern Africa, as shown in this image from May 2001. The heat wave in Pakistan that killed at least 33 people the weekend of May 5-6 is seen in yellow as a region emitting high values of thermal energy. Photo: NASA

"CERES Terra is providing an unprecedented observational basis, at just the time when major progress in understanding our environment by theory and climate modeling is taking place," said Leo Donner, a CERES science team member and climate modeler at the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory, Princeton University, Princeton, NJ.

The Terra spacecraft is part of NASA's Earth Science Enterprise, a long-term research effort being conducted to determine how human-induced and natural changes affect our global environment.