Direct and Indirect Thermospheric Heating Sources for Solar Cycles 21-23
D. J. Knipp [delores.knipp@usafa.af.mil], U.S. Air Force Academy, Colorado Springs, CO; K. Tobiska, Space Environment Technologies, Pacific Palisades, CA; and B. Emery, High Altitude Observatory, NCAR, Boulder, CO

Solar variability is often cast in terms of radiative emissions and their associated climate response; however, growing societal reliance on technology is creating more interest in day-to-day solar variability. This variability is associated with both solar radiative and solar wind emissions. In this paper we explore the combined effects of radiative and solar wind fluctuations at Earth. The combination of radiative and geomagnetic power creates an extended interval of solar maximum for the upper atmosphere. We used a trio of empirical models to estimate, over the last three solar cycles, the relative contributions of solar extreme ultraviolet (UV) power, Joule power, and particle kinetic power to the Earth’s upper atmosphere energy budget. Daily power values are derived from the models for the three sources. The SOLAR2000 solar irradiance specification model provides estimates of the daily extreme and far UV solar power input. Geomagnetic power is derived from a combination of satellite-estimated electron precipitation power and an empirical model of Joule power from hemispherically-integrated estimates of high-latitude energy deposition. In the interval 1975 to 2003, the average daily contributions were: electrons--36 GW, Joule--95 GW and solar--464 GW for a total of 596 GW. Solar wind-driven geomagnetic power provided more than 22% of the total global upper atmospheric energy. In the top 20 power events, geomagnetic power contributed 65% of the total power budget. In each of these events, Joule power alone, exceeded solar power. With rising activity, Joule power becomes the most variable element of solar-upper atmosphere interactions. We discuss our methods of power estimation and the implications of heating efficiencies of these power sources in the upper atmosphere.