Periodic change of polarity of photospheric magnetic field

TL;DR

This study investigates the periodic polarity changes in the Sun's photospheric magnetic field, revealing cyclic structures with periods of 0.5 to 4 years linked to the solar magnetic cycle polarity.

Contribution

It identifies distinct spatiotemporal regions with cyclic magnetic polarity variations using long-term synoptic maps and advanced data processing methods.

Findings

Six regions with cyclic structures identified

Maximum periods around 1.2 years observed

Amplitude of ripples linked to polar field polarity

Abstract

The work is devoted to the study of periodic structures in the magnetic field of the photosphere. The polarity of the Sun's magnetic fields shows cyclicity with periods of 1-3 years, which is possibly due to quasi-biennial variations that are found in various parameters of solar activity, interplanetary space, and in cosmic rays. In this work, variations in weak magnetic fields of the photosphere were investigated, which required the use of special data processing methods. Synoptic maps of the photospheric magnetic field for the period 1978-2016 (NSO Kitt Peak) were used. To highlight the contribution of weak magnetic fields, the saturation threshold for synoptic maps was set at 5 G. Based on thus transformed synoptic maps, a time-latitude diagram was constructed. For the selected latitude intervals, smoothing, trend removal and Fast Fourier Transform (FFT) were performed. In the time-latitude diagram, 6 spatiotemporal regions with distinct cyclic structure were observed during 4 solar cycles (21-24). The periods ranged from 0.5 to 4 years with a maximum at 1.2 years. The amplitude of ripples is significantly higher for those intervals in which the polar field had positive sign. This effect confirms the connection of ripples variations with the polarity of the 22-year magnetic cycle.