HR: 0800h
AN: SH41A-1109    [Abstracts]
TI: Lower Limit on Solar Irradiance Variation
AU: * Goode, P R
EM: pgoode@bbso.njit.edu
AF: Big Bear Solar Observatory/NJIT, 40386 N. SHore Lane, Big Bear City, CA 92314 United States
AB: Helioseismic data reveal that the historical Sun cannot be any dimmer than it is now at activity minimum. Changes in the frequencies of solar oscillations are the most precise probe of irradiance variations over the solar cycle. Using MDI data, Dziembowski and Goode (2005) showed that f-mode changes arise from the direct effect of the evolving magnetic activity, while p-mode changes are due to small, activity induced changes in convective flows very near to the solar surface (turbulent pressure). The f-modes also sharply limit the allowed field growth with activity, and the limit is consistent with the observations of Lin and Rimmele (1999). Combining MDI data with BBSO Ca II K, we find the Sun is smooth at activity minimum and becomes increasingly corrugated with rising activity. The overall physical picture is one in which the Sun is hottest and smoothest at activity minimum, and becomes cooler, more corrugated and irradiant with rising activity. Thus, these results place a lower limit on irradiance variations, consistent with current activity minima, and are roughly consistent with a picture of Spruit (2000) and the behavior of faculae as reported by Berger et al. (2005).
DE: 1650 Solar variability (7537)
DE: 7522 Helioseismology
DE: 7524 Magnetic fields
DE: 7538 Solar irradiance
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005