THE NIMBUS EARTH RADIATION BUDGET (ERB) EXPERIMENT - 1975 TO 1992

Three spectrally broadband measurement sets are presently being used f or earth radiation budget (ERB) studies. These are the Nimbus-6 ERB (J uly 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, absorb ed solar energy, outgoing longwave and net radiation. The Nimbus-7 sta rted an accurate record of the solar constant in November 1978, while a nearly continuous record of the earth's radiation budget began in Ju ly 1975 with the Nimbus-6. Both the Nimbus-6 and -7 products have, in recent years, been reprocessed with improved processing and calibratio n algorithms so that the entire dataset can be considered as new. Howe ver, because of the use of different calibration and processing proced ures, the three datasets for some purposes must be considered as piece wise continuous. Nevertheless, the data have been used in many importa nt 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 s how the earth's mean annual energy budget to be stable at the 0.2% lev el 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 tem perature. Other studies deal with the cooling and warming effects of c louds, interregional energy transport, and interannual variations. Our understanding of the sensors and how to derive an accurate mean radia tion budget from the measurements has slowly improved over the years. But to date, there has been no consensus on the use of consistent cali bration and processing procedures to permit quantitatively consistent analyses across the Nimbus-6, -7, and ERBE products. This report descr ibes some successes and lessons learned during the Nimbus ERB program and the compatibility of the Nimbus and ERBE products.