The Evolution of the Polar Coronal Holes Over a Solar Cycle

Details The Evolution of the Polar Coronal Holes Over a Solar Cycle The Evolution of the Polar Coronal Holes Over a Solar Cycle

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sp51b02h&link_type=abstract

American Geophysical Union, Spring Meeting 2001, abstract #SP51B-02

Physics

7511 Coronal Holes, 7524 Magnetic Fields, 7536 Solar Activity Cycle (2162)

Scientific paper

The polar coronal holes, areas of open magnetic field on the Sun, persist for 10 years, first appearing shortly after the completion of the polar magnetic field reversal and disappearing 1--2 years before their next reversal. We present the results of a study of the polar coronal holes observed during cycles 22 and 23 using the National Solar Observatory/Kitt Peak photospheric magnetograms and He~I 10830 spectroheliograms. The locations and boundaries of coronal holes are inferred from the He~I 10830 synoptic rotation maps. The magnetic field properties are derived by superimposing the coronal hole boundaries onto the corresponding synoptic rotation magnetograms. We find that (1) the polar holes form from high-latitude, isolated, non-polar holes that develop a few months before the completion of the polar reversal; (2) The area and magnetic flux in the polar holes initially increase rapidly, reaching their respective maxima within 1--2 years; (3) In the decline of cycle 22, the southern polar hole was smaller (3.7 x 1020 cm2) than the northern polar hole (5.1 x 1020 cm2), while both holes had the same absolute magnetic flux (3.1-3.2 x 1022 Mx); (4) The polar holes decrease in area and magnetic flux with the onset of new cycle activity, disappearing once the absolute magnetic flux in the more extended polar regions decreased below about 5 x 1021 Mx. Results on the characteristics and behavior of polar holes and their extension to lower latitude will be discussed. This work is funded through NSF Grant ATM-9713576.

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