Chinese sunspot drawings and their digitization – (III) quasi-biennial oscillation of the hand-drawn sunspot records

Abstract

Quasi-biennial Oscillations (QBOs) of the Sun have a significant meaning as a benchmark of solar cycle, not only for understanding the dynamo action but also in terms of space weather prediction. In this paper, the hand-drawn sunspot images recorded from the Purple Mountain Observatory are used to investigate the solar QBOs and the Gnevyshev gap of the sunspot relative numbers (Rs) and group sunspot numbers (Rg) during the period 1954–2011. The main results are as follows: (1) both the Rs and Rg exhibit similar periods including the 22-year magnetic cycle, the 11-year Schwabe cycle, and the QBOs modes; (2) the reconstructed QBOs of both data sets exhibit coherent behavior and tend to have a high amplitude during the maximum phase of each solar cycle; (3) the Gnevyshev gap is produced by the superposition of the QBOs and the 11-year Schwabe cycle, and the Rs is better to study the variation of the Gnevyshev gap rather than the Rg.

Periodic Variations of Solar Corona Index during 1939–2020

“…It has been paid more attention by authors recently, since its physical origin may be related to the dynamic process in the solar tachocline. Some authors studied the QBOs during the period range of 1.5 to 3-yr, but others extend the range from 1.5 to 4-yr. [13,14,16,27]. However, from the lower left panel in Figure 2, one can see that the periods around 3.5-yr have much more energy than that around 2.5-yr.…”

“…The synchrosqueezed wavelet transform (SWT) is a tool developed for extracting time-frequency information of a signal that was firstly introduced by Daubechies et al [38]. It has been widely used in various scientific fields by many authors in recent years [16,27,39,40]. By squeezing and rearranging the energy at a center frequency in the spectrum from wavelet transformation, a new spectrum with more concentrated energy on the time-frequency surface can be obtained.…”

“…During solar cycles 19-24, various fluctuations with "mid-range" periods have been detected by authors in different phases of different solar cycles, such as 51, 62, 73, 152, and 546-day [10][11][12]. A type of oscillation with periods of around two years, which have been named qusi-biennial oscillations (QBOs) of the Sun, have also been found in many indicators, and have been paid increasing attention by authors in recent decades [13][14][15][16].…”

Chinese Sunspot Drawings and Their Digitizations-(VI) Extreme Value Theory Applied to the Sunspot Number Series from the Purple Mountain Observatory

“…Ref. Wan et al (2020) [28] studied the quasi-biennial oscillations of sunspot activity based on this dataset. Therefore, the data are reliable and can be used for scientific research.…”