University of Oulu

Tanskanen, E. I., Hynönen, R. & Mursula, K. (2017). Seasonal variation of high‐latitude geomagnetic activity in individual years. Journal of Geophysical Research: Space Physics, 122, 10,058–10,071.

Seasonal variation of high‐latitude geomagnetic activity in individual years

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Author: Tanskanen, E. I.1; Hynönen, R.1; Mursula, K.2
Organizations: 1ReSoLVE Centre of Excellence, Aalto University, Espoo, Finland
2Space Climate Research Unit, ReSoLVE Centre of Excellence, Oulu University, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.6 MB)
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Language: English
Published: American Geophysical Union, 2017
Publish Date: 2019-03-05


We study the seasonal variation of high‐latitude geomagnetic activity in individual years in 1966–2014 (solar cycles 20–24) by identifying the most active and the second most active season based on westward electrojet indices AL (1966–2014) and IL (1995–2014). The annual maximum is found at either equinox in two thirds and at either solstice in one third of the years examined. The traditional two‐equinox maximum pattern is found in roughly one fourth of the years. We found that the seasonal variation of high‐latitude geomagnetic activity closely follows the solar wind speed. While the mechanisms leading to the two‐equinox maxima pattern are in operation, the long‐term change of solar wind speed tends to mask the effect of these mechanisms for individual years. Large cycle‐to‐cycle variation is found in the seasonal pattern: equinox maxima are more common during cycles 21 and 22 than in cycles 23 or 24. Exceptionally long winter dominance in high‐latitude activity and solar wind speed is seen in the declining phase of cycle 23, after the appearance of the long‐lasting low‐latitude coronal hole.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 122
Issue: 10
Pages: 10,058 - 10,071
DOI: 10.1002/2017JA024276
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: We acknowledge the financial support by the Academy of Finland to the ReSoLVE Centre of Excellence (project 272157).
Academy of Finland Grant Number: 272157
Detailed Information: 272157 (Academy of Finland Funding decision)
Copyright information: © 2017. American Geophysical Union. All Rights Reserved.