Height stratification of solar magnetic fields in cycles 2123

  • N.N. Stepanian Crimean Astrophysical Observatory
  • Z.S. Akhtemov Crimean Astrophysical Observatory
  • V.G. Fainstein Институт солнечно-земной физики СО РАН, Иркутск, Российская Федерация, 664033
  • G.V. Rudenko Институт солнечно-земной физики СО РАН, Иркутск, Российская Федерация, 664033

Abstract

The radial component of the solar magnetic field Br was calculated in the potential approximation in the height range from 1 to 2.5 solar radius Rʘ. According to these data synoptic maps of the magnetic field for solar cycles 21-23 were constructed. For every 10-degree latitude zone the proportion of its area S+field, occupied by "+" field in each solar rotation was found. In the entire latitude zone a radial component of the field is assumed to be positive, if S+field £ 80% and negative - if S+field £ 20%. The field proved to be virtually unipolar at the level of the photosphere (R = Rʘ) during most of the cycle, from the poles to the north and south latitude ≈ 60 °. In the vicinity of minimum between cycles 21 and 22, and cycles 22 and 23 for a few rotations of the Sun the field is almost unipolar at latitudes (40°)-90 °. At R = 2.5Rʘ for most of each cycle the unipolar field was observed in the latitude range (20°-(90°)), and (20°-90°). According to our interpretation, the shift of the boundaries of the polar field to the equator with height reflects superradial expansion of open magnetic flux tubes from the polar coronal holes. It was found that the reversal of the polar fields begins 1-2 rotations, and finishes from 2 to 14 solar rotations before at high heights than at the surface of the Sun. This indicates that the first large-scale field reversal occurs, and then the small-scale. In the study of the sector structure of the magnetic field at different heights, it was found that the boundaries, rotating with a period of less than Carrington one, extend to greater heights than the boundaries with Carrington and a longer period. We assume that the boundaries of the first type are formed by the large-scale structure of the magnetic field, the boundaries of the second type are determined by active regions.

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