Physics
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009spd....40.1113f&link_type=abstract
American Astronomical Society, SPD meeting #40, #11.13; Bulletin of the American Astronomical Society, Vol. 41, p.827
Physics
Scientific paper
Total solar irradiance (TSI) values measured during the present activity minimum by the VIRGO, ACRIM, and TIM radiometers are significantly ( 0.018% +/- 0.006 % rms) lower than reported during the last minimum in 1996 (1). This decrease represents 1/4 the amplitude of 11 - yr TSI variation. Differences in spots, faculae and active network cannot account for this anomalous decrease. A sufficient difference in the TSI contribution from quiet network also seems unlikely, since the solar microwave flux index, F10.7, has dipped only 4 % below its 1996 minimum. This is an order of magnitude less than required to explain the TSI decrease by a decline in network area.
The remaining explanation in terms of photospheric magnetic structures, might lie in a decrease in the area of polar faculae, whose cycle amplitude is presently at a minimum for this century. We evaluate their TSI contribution using area and contrast measurements with the Solar Bolometric Imager (SBI), together with polar facula counts (2). We find that their TSI contribution between the present and 1996 activity minima, is below 0.002%. This is again, an order of magnitude below the observed TSI decrease.
We conclude that the anomalous TSI decrease is unlikely to be caused by photospheric magnetic changes. This suggests that solar luminosity may be able to change significantly over decadal time scales through an as- yet- unidentified, relatively shallow mechanism that avoids the 10*5 year thermal relaxation time of the solar convection zone.
This work was supported at Heliophysics, Inc by NSF grant ATM 0718305, and at APL by NASA grant NNG 05WC07G
References:
1. Frohlich, C. 2008, AGU Fall Meeting, Abstract # SH21C-05.
2. Sheeley, N. 2008, Ap.J. , 680, 1553.
Bernasconi Pietro
Foukal Peter V.
Fröhlich Carla
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