Researchers reveal hemispheric asymmetry in long-term sunspot activity

(ORDO NEWS) — PhD Zhang Xiaojuan and Professor Deng Linhua of the Yunnan Observatory of the Chinese Academy of Sciences investigated the temporal variation in the hemispheric distribution of long-term sunspot activity from 1939 to 2019.

Sunspots are the most easily visible structures in the photosphere. They are associated with most activity phenomena such as filaments, flares and coronal mass ejections. The relative number of sunspots is a measure of global magnetic activity.

According to the latest dynamo theories, solar activity is not the same in the two hemispheres; there is always hemispheric asymmetry. Hemispherical asymmetry is not an artifact of inaccurate or noisy observations, but a real feature of the solar cycle.

Studying the time evolution of solar cycles in two different hemispheres can provide important information about the dynamo process underlying this evolution.

In this paper, the researchers studied the temporal and spatial behavior of the hemispheric asymmetry in the relative number of sunspots, covering eight solar cycles (from March 1939 to November 2019).

According to cross-correlation analysis, the researchers found that relative sunspot numbers are highly correlated with international sunspot numbers.

In addition, the time analysis shows an increase in power in the ranges of periods of quasi-biennial fluctuations, about nine years, between 30 and 50 years. The results of the analysis show a possible mechanism responsible for the generation and variations of hemispherical coupling on the Sun.


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