Researchers reveal hemispheric asymmetry of long-term sunspot activity

Credit: Pixabay/CC0 Public Domain

Ph.D. candidate Zhang Xiaojuan and Prof. Deng Linhua from Yunnan Observatories of the Chinese Academy of Sciences investigated the temporal variation of the hemispheric distribution of long-term sunspot activity during the time interval from 1939 to 2019.

This work was published in Monthly Notices of the Royal Astronomical Society.

Solar sunspots are the most easily visible structures in the photosphere. They are connected to most activity phenomena, such as filaments, flares and . Sunspot relative numbers are the measure of the global magnetic activity.

According to the latest dynamo theories, is not identical in the two hemispheres, i.e., there is always a hemispheric asymmetry. The hemispheric asymmetry is not an artifact of inaccurate or noisy observations, but a real feature of the solar cycle.

Studies of the temporal evolution of the solar cycles in the two separate hemispheres can provide important information for the dynamo process underlying this evolution.

In this study, the researchers investigated the temporal and spatial behaviors of the hemispheric asymmetry of relative numbers covering eight solar cycles (from March 1939 to November 2019). The solar data used in this study is a new sunspot database, which is obtained from the Mitaka observatory of the National Astronomical Observatory of Japan (NAOJ/Mitaka).

According to the cross-correlation analysis, the researchers found that the NAOJ/Mitaka sunspot relative numbers were highly correlated with the international sunspot numbers obtained from the World Data Center Sunspot Index and Long-term Solar Observations, which confirmed that the Mitaka sunspot time series could be used for hemispheric variation study.

Furthermore, for the temporal analysis, there are enhanced powers in the period ranges of quasi-biennial oscillations, around nine years, between 30 and 50 years. The analysis results reveal a possible mechanism responsible for the generation and variation of the hemispheric coupling in the sun.

More information: X J Zhang et al, Hemispheric asymmetry of long-term sunspot activity: Sunspot relative numbers for 1939-2019, Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac1231

Citation: Researchers reveal hemispheric asymmetry of long-term sunspot activity (2022, May 24) retrieved 25 September 2023 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Explore further

NASA's SDO watches a sunspot turn toward Earth


Feedback to editors