The Nimbus Earth Radiation Budget (ERB) Experiment: 1975 to 1992

Abstract

Three spectrally broadband measurement sets are presently being used for earth radiation budget (ERB) studies. These are the Nimbus-6 ERB (July 1975 to June 1978), the Nimbus-7 ERB (November 1978 to the present), and the Earth Radiation Budget Experiment (ERBE) (November 1984 to present). The measurements yield the incident solar irradiance, absorbed solar energy, outgoing longwave and net radiation. The Nimbus-7 started an accurate record of the solar constant in November 1978, while a needy continuous record of the earth's radiation budget began in July 1975 with the Nimbus-6. Both the Nimbus-6 and -7 products have, In recent years, been reprocessed with improved processing and calibration algorithms so that the entire dataset can be considered as new. However, because of the use of different calibration and processing procedures, the three datasets for some purposes must be considered as piecewise continuous. Nevertheless, the data have been used in many important climate studies. The Nimbus-7 solar measurements indicate that the sun is a low-level variable star and that the mean annual solar energy just outside the earth's atmosphere was about 0.1% lower in 1984 than in 1979 and 1991. Further, the 9 years of Nimbus-7 ERB measurements show the earth's mean annual energy budget to be stable at the 0.2% level with apparently real changes in the annual emitted longwave at the 0.1% to 0.2% level that are associated with changes in the surface temperature. Other studies deal with the cooling and warming effects of clouds, interregional energy transport, and interannual variations. Our understanding of the sensors and how to derive an accurate mean radiation budget from the measurements has slowly improved over the years. But to date, there has been no consensus on the use of consistent calibration and processing procedures to permit quantitatively consistent analyses across the Nimbus-6, -7, and EABE products. This report describes some successes and lessons learned during the Nimbus ERB program and the compatibility of the Nimbus and ERBE products.