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J. M. Pap (Goddard Earth Sciences and Technology Center, University of Maryland, Baltimore County)
As the solar energy flux is deposited in various parts of the Earth's atmosphere, oceans, and land, it controls the heating, ionization, radiative, chemical, and dynamical processes characterizing the terrestrial atmosphere and climate system. Therefore, the accurate knowledge of the solar energy received by Earth and understanding its variability are critical issues for an understanding of the climate response to the increasing greenhouse gas concentrations. Solar irradiance (both bolometric and at UV wavelengths) has been measured continuously from various space platforms since late 1978. These irradiance measurements established conclusively that solar irradiance varies on time scales from minutes to decades. The most important discovery of the space-based irradiance measurements is that total irradiance varies with about 0.1% over the solar cycle, being higher during maximum activity conditions. Since even small variations in total irradiance over long time scales may lead to climate changes, it is extremely important (1) to maintain a long-term high precision irradiance data base for climate studies and (2) to understand the underlying physical mechanisms. In this paper we summarize the results gained from the multi-decade long space-based irradiance measurements.
This research was supported by a grant NAG5-10876 from the SOHO Office of NASA's Office of Space Science and by NASA grants NAG5-9207 and NAG5-11326 from NASA's Office of Earth Science. SOHO is a mission of international cooperation between ESA and NASA.