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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 29, issue 10
Ann. Geophys., 29, 1783–1792, 2011
https://doi.org/10.5194/angeo-29-1783-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 29, 1783–1792, 2011
https://doi.org/10.5194/angeo-29-1783-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

  11 Oct 2011

11 Oct 2011

Climatology of rapid geomagnetic variations at high latitudes over two solar cycles

A. Viljanen1 and E. Tanskanen1,2 A. Viljanen and E. Tanskanen
  • 1Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
  • 2University of Bergen, Dept. of Physics and Technology, Allégatan 55, Bergen 5007, Norway

Abstract. We investigate the characteristics of rapid geomagnetic variations at high latitudes based on the occurrence of large time derivatives of the horizontal magnetic field (dH/dt exceeding 1 nT s−1). Analysis of IMAGE magnetometer data from North Europe in 1983–2010, covering more than two solar cycles, confirms and specifies several previous findings. We show that dH/dt activity is high around the midnight and early morning hours, and nearly vanishes at noon and early afternoon. This happens during all seasons, although the midnight maximum is nearly invisible during summer. As indicated by modelled ionospheric equivalent currents, large dH/dt values occur predominantly during westward ionospheric electrojets. Before and around midnight, dH/dt tends to be north-south oriented, whereas in the morning hours, its direction is more west-east directed. dH/dt tends to be more strictly north-south oriented during winter than other seasons. The seasonal occurrence of large dH/dt values is similar to the variation of the maximum amplitude of westward equivalent currents. The yearly fraction of east-west directed large dH/dt vectors at the Kilpisjärvi station (MLAT 65.88) varies from 31 to 47 % without any clear correlation with the general geomagnetic activity nor with the yearly averages of solar wind parameters.

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