Intensity variation of the HeI 10 830 Å line during the solar activity cycle

Details Intensity variation of the HeI 10 830 Å line during the solar activity cycle Intensity variation of the HeI 10 830 Å line during the solar activity cycle

Jul 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998arep...42..528k&link_type=abstract

Astronomy Reports, Volume 42, Issue 4, July 1998, pp.528-533

Astronomy and Astrophysics

Astronomy

1

Scientific paper

New observations of solar active and quiet regions in the HeI 10 830 IR triplet obtained from 1976 to 1997 are presented. The good correlation of the depth of the main component with the phase of the 11-year solar cycle makes it possible to use this quantity as a solar activity index on both long time scales (years) and on shorter time scales of the order of a month. Advantages of this new activity index in comparison with commonly used indices, such as the Wolf number, are shown. The 1996-1997 observations indicate that: (a) the minimum of the 22nd cycle is deeper that the minimum of the 21st cycle, and (b) the Sun came out of its phase of minimum activity and began its 23rd cycle in 1997. In the transition from the minimum to the maximum of the cycle, the depth of the He I 10830 Angstrom line in quiet regions roughly doubles, while the corresponding depth increase is substantially less in active regions (<=30%). This appears to indicate that the background magnetic fields vary during the course of the cycle more strongly than the local fields associated with sunspots, faculae, and activity complexes. It is proposed to use regular observations of the He I 10830 Angstrom line to predict solar activity.

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