Seasonal Variation of High-Latitude Geomagnetic Activity in Individual Years

Research output: Contribution to journalArticleScientificpeer-review

Researchers

Research units

  • University of Oulu

Abstract

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.

Details

Original languageEnglish
Pages (from-to)10,058–10,071
Number of pages14
JournalJournal of geophysical research: Space physics
Volume122
Issue number10
Publication statusPublished - 21 Nov 2017
MoE publication typeA1 Journal article-refereed

    Research areas

  • Decadal time scales, Geomagnetic activity, Seasonal variation, Solar cycle-to-cycle variation, Solar wind-magnetosphere coupling, Sun-Earth coupling

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