At substorm onset, 40% of AL comes from underground

EI Tanskanen*, A Viljanen, TI Pulkkinen, R Pirjola, L Hakkinen, A Pulkkinen, O Amm

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Magnetic variations observed at the Earth's surface are caused by external and internal sources. External variations arise from currents in the ionosphere and magnetosphere, and internal variations arise from currents induced in the solid Earth. In this paper we examine how large the internal contribution is to magnetic variations measured at the Earth's surface. We use IMAGE magnetometer measurements to analyze 77 substorms during 1997. For each event we evaluate the internal. and external parts of a locally derived auroral electrojet index (IL index). The magnetic field separation is performed using the Siebert-Kertz equations. A superposed epoch analysis of all events clearly shows that the internal contribution peaks strongly at substorm onset, when the internal contribution is similar to 40% of the total field. After the substorm peak intensity, the internal contribution decreases almost linearly to the quiet time value of 10-20%. The induction effects are largest during the times of rapid changes and at stations located over the Arctic Ocean.

Original languageEnglish
Pages (from-to)13119-13134
Number of pages16
JournalJournal of Geophysical Research
Volume106
Issue numberA7
DOIs
Publication statusPublished - 1 Jul 2001
MoE publication typeA1 Journal article-refereed

Keywords

  • FIELD-ALIGNED CURRENTS
  • IONOSPHERIC ELECTRIC-FIELDS
  • GROUND-BASED OBSERVATIONS
  • COMPLEX IMAGE METHOD
  • AURORAL ELECTROJET
  • GEOMAGNETIC-ACTIVITY
  • MAGNETOMETER ARRAY
  • CONDUCTIVITY
  • SITUATIONS
  • EVOLUTION

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