PROGRAM TITLE: Solar Studies/Global Change ACTIVITY STREAM: Observation SCIENCE ELEMENT:Solar Influences SMITHSONIAN INSTITUTION SMITHSONIAN ASTROPHYSICAL OBSERVATORY (SAO) SCIENTIFIC MERIT: The influence of the sun and its inputs to the terrestrial atmosphere both in particle deposition and solar radiation are critical elements in the overall understanding of global change. The near constancy of solar output in the visible region of the spectrum provides the earth with the steady source of radiative input required to create the stable weather conditions which have permitted terrestrial life to flourish. There is suggestive evidence of a direct link between long-term changes in solar irradience and global warming/cooling. The solar shortwave radiative output (far ultraviolet, extreme ultraviolet (EUV), x-ray, gamma ray radiations) and solar particle output (solar wind, high-energy accelerated particles from flares) is highly variable and depends on solar activity. The EUV, for instance, drives the chemical reactions, controls the energy balance, and powers the dynamical processes in the upper atmosphere, and through physical, chemical, and electromagnetic couplings, influences the chemistry and dynamics of other atmospheric regions. However, direct measurements of the solar EUV flux have been very limited. There is a need for more empirical and theoretical work on the behavior of the solar activity cycle and the relationship between solar activity and changes in solar irradience in order to establish or refute connections between solar activity/irradience and global change. In addition, as part of an overall program of solar irradience monitoring, an instrument must be developed to carry out in-orbit, regular, accurately calibrated measurements of the solar EUV flux over a long time period. In order to understand the causes of solar variability and improve our capabilities in making solar predictions, we need to investigate the basic physical processes responsible for solar activity. Solar theorists are needed who can explore the detailed interactions between solar magnetic fields and plasmas. In order to study the relationship between the solar activity cycle and luminosity (irradience) variations, measurements of stellar activity cycles for solar-like stars will be carried out. We propose to continue and to strengthen our program in observing stellar activity cycles using existing equipment and our new robotic Automatic Photoelectric Telescopes. Because the radiometric sensitivity of an EUV spectrometer changes during its use, it is necessary to develop an instrument which can make accurate long-term, calibrated, spectrally-resolved irradience measurements. Two methods of achieving radiometric accuracy in the EUV are being studied: (1) use of absolute detectors, and (2) use of "standard" sources. STAKEHOLDERS: Nearly all the solar research at SAO addresses the basic physics behind the variations in the solar output of radiation and particles. SAO scientists are studying chromospheric and coronal heating, the heating and accelerations of the solar wind, solar activity, the structure of the solar atmosphere, and the role of the solar magnetic field in these phenomena. SAO has two instruments under development for empirically studying the origins of the solar wind, and for probing the solar interior by seismology techniques. Funded by NASA and AFOSR, laboratory activities are underway to develop an absolute extreme-ultraviolet solar spectral irradience monitor which can be recalibrated reliably in-orbit. POLICY RELEVANCE: A knowledge of the spectral distribution of solar radiation reaching the earth's surface depends on the irradience emitted by the sun -- as outlined in the STIB Core Project of the IGBP. The scientific objectives of the above research program also respond to a number of key milestones in section 2(c) -- Global Water, Energy Cycles, and Sea Level Change (Atmospheric Radiation, Clouds and Precipitation) of the USGRCP Implementation Plan, including Solar forecasting improved, Solar-climate hypotheses tested, Solar influences quantified, and Solar particle interaction with global atmosphere defined. The need for improved solar EUV flux measurements has also been called for in a number of reports that urge a national effort to provide accurate solar EUV flux data on a regular basis. Representative examples of such reports are: (1) The National Research Council Report "Long-Term Solar-Terrestrial Observations" (1988); (2) The "Report of the [NASA] Working Group on Predictions of Solar Activity and the Atmospheric Response" (1989); (3) The RISE (Radiative Inputs of the Sun to Earth) Report, a "Research Plan for the 1990's on Solar Irradience Variation", prepared for the Division of Atmospheric Sciences of the National Science Foundation (1990). PROGRAM CONTACTS:SI SGCR Representative: Ted A. Maxwell NASM MRC 315 Smithsonian Institution Washington, D.C. 20560 202 357 1424 FAX: 202 786 2566 Email: tmaxwell@ceps.nasm.edu Bureau Representative: Kate Kirby Smithsonian Astrophysical Observatory 60 Garden St. MS-14 Cambridge, MA 02138 617 495 7237 or 9524 FAX: 617 495 5970