Variations in Daily Maximum Areas and Longitudinal Widths of Solar Coronal Holes in 2017–2020

Alexandr Riehokainen,Polina Strekalova,Alexander Solov’Ev,Ivan Zhivanovich,Firas Al-Hamadani,Victoria Smirnova,Andrey Tlatov

doi:10.3390/universe8030158

Alexandr Riehokainen, Polina Strekalova + Show 5 more

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https://doi.org/10.3390/universe8030158

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Abstract

We considered coronal holes as a manifestation of the large-scale magnetic field of the Sun. The main goal of this work was to study the variations in the largest areas and longitudinal widths of solar coronal holes observed daily in the polar and mid-latitude zones on a time scale of 984 days. Statistical methods of fast Fourier transform (FFT), wavelet transform, and empirical mode decomposition (EMD) were used to detect periodicity in the variations of the considered parameters. Long-term variations in the daily measured areas and longitudinal widths of the largest solar coronal holes with periods of 8–9, 13–15, and 26–29 days were detected in three zones of the Sun: polar (north and south) and equatorial. The obtained periods are most clearly visible at the equatorial zone. In the polar zones the period of 8–9 days has a weak amplitude. We interpreted variations with periods of 8–9, 13–15, and 26–29 days as a rotation of the six-, four-, and two-sector structure of the large-scale solar magnetic field.

Highlights

Coronal holes (CHs) are structures with an open configuration of a magnetic field
We found the chains of shifts of coronal holes from day d to d + 1, measuring their Carrington latitude and longitude every day
This figure clearly shows a long period of change in the considered parameters of coronal holes

Summary

Introduction

Coronal holes (CHs) are structures with an open configuration of a magnetic field Due to this configuration of the magnetic field, charged particles can escape from the corona, forming solar wind (for more details see [1,2]), which has an important effect on space weather [3]. The study of the CH structures, their origin, and various physical parameters is important for understanding the complex processes of cyclic solar activity. Coronal holes are visible throughout the solar disk. They can be divided into polar and mid-latitude (or equatorial) coronal holes. Polar CHs are one of the longest-lived structures of the Sun; in accordance with [4], equatorial coronal holes may live more than 18 months and polar coronal holes may live

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