Equatorial electrojet as a diagnostic tool of geomagnetic field models

Heather McCreadie*, Toshihiko Iyemori

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)
117 Downloads (Pure)

Abstract

The equatorial electrojet (EEJ) is a unique feature of the Earth's external current systems because it must flow along the dip equator. This provides us with a tool to determine the nature of the variations imposed by competing main field models on the equatorial region. First we show that for certain regions a comparison between scalar geomagnetic measurements that use different models to remove the main field may not be reasonable. Next we found the intrinsic error in the determination of the possible location of the dip equator was +/- 9.8 km (0.088 degrees) at 108 km altitude for the models shown here. Using scalar measurements from over 14,000 CHAMP satellite passes, the latitude of the maximum of the EEJ field at the satellite altitude was determined by subtracting four different models of the main field. We find that the location can be statistically determined to within +/- 0.5 degrees of the dip equator (calculated at 108 km altitude) irrespective of longitude, time of the measurement, degree of magnetic activity, and subtracted model. However, variations of the latitude of the maximum EEJ field with longitude are sometimes caused by the actual model and are not always a physical phenomenon. By choosing one model, and assuming it is the best representation of the main field, we have also shown that the accuracy of determination of the position of the EEJ signal is reduced in the morning and evening hours and that a morning and evening shift in the location of the EEJ found using ground measurements is also seen here. There exists a clear annual variation in the position of the EEJ regardless of longitude: it is south of the dip equator in December which is in agreement with the findings of all previous studies.

Original languageEnglish
Pages (from-to)885-893
Number of pages9
JournalEarth, Planets and Space
Volume58
Issue number7
Publication statusPublished - 26 Jul 2006

Keywords

  • equatorial electrojet
  • geomagnetic field
  • lithospheric field
  • main field modelling
  • core field
  • CHAMP
  • Oersted
  • DAILY VARIATION SR
  • VECTOR DATA

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