Relationship of Coronal Holes at Mid and Low Latitudes to the Mean Magnetic Field of the Sun
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RELATIONSHIP OF CORONAL HOLES AT MID AND LOW LATITUDES TO THE MEAN MAGNETIC FIELD OF THE SUN
Z. S. Akhtemov, Y. T. Tsap, V. I. Haneychuk
The relationship between the magnetic fluxes and areas of coronal holes (CH) at mid and low latitudes
| M | 60o and the mean magnetic field (MMF) of the sun over the period from January 19 through December 12, 2012, is studied using ultraviolet images and magnetograms obtained with the Solar Dynamics Observatory satellite. It is shown that the boundaries of the CH determined with the algorithms CHIMERA (https://solarmonitor.org) and SPoCA (https://helioviewer.org) differ significantly. The correlation coefficient between the weighted total area of CHs taking into account the magnetic field polarity and MMF are in the range from 0.82 to 0.88. The CH can make a substantial contribution to the MMF since their fields have an open configuration and are not balanced on the solar disk. In light of the solar dynamo theory and the results obtained here, the annual time delays between the maxima of the Wolf numbers and the values of the MMF are discussed. Keywords: Sun: coronal holes: mean magnetic field
1. Introduction
At present there is no doubt that the fast (500-800 km/s) solar wind which has a significant effect on the surrounding cosmic space and the earth’s magnetosphere is formed in coronal holes (CH), i.e., in large-scale unipolar
FGBUN “KrAO RAN” (Crimean Astrophysical Observatory, CrAO), Nauchnyi, Crimea; e-mail: [email protected]
Original article submitted September 6, 2019; accepted for publication June 24, 2020. Astrofizika, Vol. 63, No. 3, pp. 451-461 (August 2020)
Translated from
0571-7256/19/6303-0399 ©2020 Springer Science+Business Media, LLC
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magnetic regions with a reduced coronal density and temperature [1-4]. The magnetic fields of CH usually have an open configuration and sometimes occupy substantial areas at mid and low latitudes. Along with the fields of other structures, they contribute to the mean magnetic field (MMF), which is in fact a measure of the disbalance of the magnetic fluxes on the solar disk [3]. According to some models of the solar dynamo, the transformation of the toroidal component of the sun’s magnetic field into a poloidal field can take place, not only near the tachocline or in the convective zone, but also on the surface of the sun [3]. It follows from the Babcock-Leighton model [5,6] that the magnetic fields of active regions must determine the main characteristics of the solar cycle and, thereby, affect many processes on the sun, including the MMF. This assumes the existence of a close coupling between the MMF and active regions. This implies a need for detailed study of the contribution of different magnetic structures to the MMF. We note that here and in the following, if not specially noted, that the MMF is taken to mean both the photospheric field averaged over the disk, Bmean, and the magnetic field of the sun as a star, Bstar, assuming that these values are equivalent. While the CH are concentrated in the region of the p
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