31 Aug 2022
31 Aug 2022
Status: this preprint is open for discussion.

Drivers of rapid geomagnetic variations at high latitudes

Liisa Juusola1, Ari Viljanen1, Andrew P. Dimock2, Mirjam Kellinsalmi1, Audrey Schillings3, and James M. Weygand4 Liisa Juusola et al.
  • 1Finnish Meteorological Institute, Helsinki, Finland
  • 2Swedish Institute of Space Physics, Uppsala, Sweden
  • 3Department of Physics, Umeå University, Umeå, Sweden
  • 4Department of Earth, Planetary, and Space Sciences, University of California Los Angeles, Los Angeles, CA, USA

Abstract. We have examined the most intense external (magnetospheric and ionospheric) and internal (induced) |dH/dt| (amplitude of the 10 s time derivative of the horizontal geomagnetic field) events observed by the high-latitude International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers between 1994 and 2018. While the most intense external |dH/dt| events at adjacent stations typically occurred simultaneously, the most intense internal (and total) |dH/dt| events were more scattered in time, most likely due to the complexity of induction in the conducting ground. The most intense external |dH/dt| events occurred during geomagnetic storms, among which the Halloween storm in Oct 2003 featured prominently, and drove intense geomagnetically induced currents (GIC). Events in the prenoon local time sector were associated with sudden commencements (SC) and pulsations, and the most intense |dH/dt| values were driven by abrupt changes in the eastward electrojet due to solar wind dynamic pressure increase or decrease. Events in the premidnight and dawn local time sectors were associated with substorm activity, and the most intense |dH/dt| values were driven by abrupt changes in the westward electrojet, such as weakening and poleward retreat (premidnight) or undulation (dawn). Despite being associated with various event types and occurring at different local time sectors, there were common features among the drivers of most intense external |dH/dt| values: pre-existing intense ionospheric currents (SC events were an exception) that were abruptly modified by sudden changes in the magnetospheric magnetic field configuration. While proper description of the fast changes during SC events appears to require 1 s data, pulsations and substorms may be sufficiently described by 10 s |dH/dt|. 1 min data, however, significantly underestimates the |dH/dt| peaks. Our results contribute towards the ultimate goal of reliable forecasts of dH/dt and GIC.

Liisa Juusola et al.

Status: open (until 27 Oct 2022)

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  • RC1: 'Comment on egusphere-2022-850', Mark Engebretson, 14 Sep 2022 reply

Liisa Juusola et al.


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Short summary
We have examined events during which the measured magnetic field on the ground changes very rapidly, causing a risk to technological conductor networks. According to our results, such events occur when strong electric currents in the ionosphere at 100 km altitude are abruptly modified by sudden compression or expansion of the magnetospheric magnetic field farther in space.