CERES, a three-channel radiometer, measures both solar-reflected and Earth-emitted radiation from the top of the atmosphere to the surface. It also determines cloud properties including the amount, height, thickness, particle size, and phase of clouds using simultaneous measurements by other instruments. These measurements are critical for understanding cloud-radiation climate change and improving the prediction of global warming using climate models. CERES instruments also fly on the TRMM, Terra, and Aqua satellites.
The Clouds and the Earth's Radiant Energy System (CERES) instrument measures reflected sunlight and Earth-emitted thermal radiation - essentially Earth's energy budget. The sun's radiant energy is the fuel that drives Earth's climate engine and the Earth-atmosphere system constantly tries to maintain a balance between the energy that reaches the Earth from the sun and the energy that flows from Earth back out to space.
The CERES instrument has three channels -- a shortwave channel to measure reflected sunlight, a longwave channel to measure Earth-emitted thermal radiation in the 8-12 µm "window" region, and a total channel to measure all wavelengths of radiation. Onboard calibration sources include a solar diffuser, a tungsten lamp system with a stability monitor, and a pair of blackbodies that can be controlled at different temperatures. Cold space looks and internal calibration are performed during normal Earth scans. The CERES swath is from limb to limb and the instrument has cross-track and 360-degree azimuth biaxial scan angular sampling capabilities.
The CERES global observations provide new data for improving seasonal-to-interannual climate forecasts, including the cloud and radiative aspects of periodic large-scale climate events such as El Niño. CERES data can be used for evaluating the radiative effects and climatic impact of natural disasters, such as volcanic eruptions and major floods and droughts. The long-term CERES data set will provide a basis for scientific understanding of the mechanisms and factors such as cloud/climate feedback that determine long-term climate variations and trends.
CERES Flight Model 5 (FM5) is the next in a long line of climate measurements. The first CERES instrument was launched aboard the Tropical Rainfall Measurement Mission (TRMM) satellite more than 10 years ago. Currently, there are four CERES instruments operating on two satellites (Terra and Aqua). The CERES instrument is based on the successful ERBE scanning radiometer design with several improvements to accommodate upgraded performance requirements and hardware developments. CERES has twice the spatial resolution and improved instrument calibration.
The CERES FM 5 instrument is managed by the NASA Langley Research Center in Hampton, Virginia, and built by Northrop Grumman Space Technologies in Redondo Beach, California.
Radiation and clouds strongly influence our weather and climate. For example, low, thick clouds reflect incoming solar radiation back to space causing cooling. High clouds trap outgoing infrared radiation and produce greenhouse warming. The Earth Radiation Budget Experiment (ERBE), which was launched on multiple satellite in the mid 1980s, and now the EOS CERES instruments, are providing critical data on the effect of clouds on climate. The data indicate that clouds have an overall net cooling effect on the Earth (i.e., negative net cloud forcing in the figure below). The largest negative cloud forcing is found over the storm tracks at high-to-middle latitudes in the summer hemisphere. The most extreme values occur over marine areas, since the contrast in albedo between clear and cloudy conditions is greatest over oceans. In the tropics, the longwave and shortwave cloud forcings nearly cancel; therefore clouds have neither a heating nor cooling effect in these areas. Much more information is needed about clouds and radiation and their role in climate change. The largest uncertainty in climate prediction models is how to determine the radiative and physical properties of clouds. CERES observations will contribute to improving the scientific understanding of the mechanisms and factors that determine long-term climate variations and trends.
Global observations of clouds and radiation provide for better scientific understanding to improve seasonal-to-interannual climate forecasts. For example, early CERES data from TRMM show that the El Niño/Southern Oscillation (ENSO) has a pronounced radiative pattern across the Pacific basin, with increased deep convection in the eastern tropical Pacific and more clear sky conditions in the western tropical Pacific. Strong shortwave and longwave radiative anomalies (i.e., differences from a 5-year average from ERBE) were observed during the latter phase of the 1997-98 ENSO event. The radiative features are closely related to cloud amount, type, and thickness. CERES provides accurate radiation data as well as imager-derived cloud physical and microphysical properties needed to improve our knowledge of such large-scale climate perturbations.
CERES provides global data for evaluating the radiative effects and climatic impact of natural events such as volcanic eruptions and major floods and droughts. Volcanic activity has long been suspected of causing significant short-term changes in climate. Powerful volcanic eruptions typically inject huge quantities of gases into the stratosphere, forming an aerosol layer that can remain in the atmosphere for several years. Cooling was so severe following the Tambora eruption in Indonesia that 1816 was called "the year without a summer." Cold temperatures (snow fell in August) and killing frosts in Europe and America caused extensive crop failures and famine. The 1883 eruption of Krakatoa was heard 3,000 miles away and produced sea waves almost 40 meters high. The vast stratospheric cloud caused such vivid red sunset afterglows that firemen were called out in several cities to quench the apparent conflagration. The volcanic cloud that created such spectacular atmospheric effects also acted as a solar radiation filter, lowering global temperatures as much as 1.2oC in the year after the eruption. Temperatures did not return to normal until 1888.
In 1991, a series of spectacular eruptions of Mount Pinatubo in the Philippines produced the greatest volcanic clouds observed since the beginning of the satellite era. This event presented an unprecedented opportunity for an experiment in climate change. Radiative heat flow (or flux) anomalies derived from ERBE were used to determine the volcanic radiative forcing following the eruption of Mount Pinatubo. Aerosols altered the Earth's radiation balance by reflecting more of the Sun's energy back to space as indicated by the yellow and red areas in the shortwave anomaly figure on the right. The Earth continued to cool radiatively at about the same rate as before the eruption. The resulting cooling of the atmosphere and the surface depressed the mean global temperature by some 0.5-1.0oC.
Following any future major volcanic eruption, simultaneous observations of radiation and clouds by CERES and other EOS instruments will yield important new data on how clouds and the climate are affected by the volcanic particles.
While satellites measure radiative flux at the top of the atmosphere, most people are more concerned about conditions on the surface where we live, grow our crops, heat and cool our homes, and enjoy our skiing or beach vacations. Consequently, one of the objectives of the CERES investigation is to better estimate radiative fluxes within the atmosphere and at the surface. CERES surface radiation budget (SRB) data help us understand the trends and patterns of changes in regional land cover, biodiversity, and agricultural production. In particular, CERES can detect variations in surface albedo and longwave emission that signal potential changes in the nature of the land, such as desertification. The SRB provides data on solar energy available at the surface (as shown in the figure below from the Global Energy and Water-cycle Experiment SRB project), useful for locating sites for solar power facilities and for architectural design applications.