Theory of Cowling channel formation by reflection of shear Alfven waves from the auroral ionosphere

A. Yoshikawa, O. Amm, H. Vanhamäki, A. Nakamizo, R. Fujii

Research output: Contribution to journalArticle

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Abstract

We present the first complete formulation of the coupling between the ionospheric horizontal currents (including Hall currents) and the field-aligned currents (FAC) via shear Alfven waves, which can describe the formation of a Cowling channel without any a priori parameterization of the secondary (Hall polarization) electric field strength. Our theory reorganizes the Cowling channel by "primary" and "secondary" fields. Until now there are no theoretical frameworks, which can derive these separated components from observed or given total conductance, electric field, and FAC distributions alone. But when a given incident where Alfven wave is considered as the driver, the reflected wave can be uniquely decomposed into the primary and secondary components. We show that the reflected wave can, depending on actual conditions, indeed carry FAC that connect to divergent Hall currents. With this new method, we can identify how large the secondary electric field becomes, how efficiently the divergent Hall current is closed within the ionosphere, and how much of the Hall current continues out to the magnetosphere as FAC. In typical ionospheric situations, only a small fraction of FAC is connected to Hall currents at conductance gradients, i.e., the secondary field is relatively strong. But when conductances are relatively low compared with Alfven conductance and/or horizontal scales smaller than ~10 km, the Hall FAC may become significant. Key Points Formation of Cowling channel coupling to the shear Alfven wave Identify the polarization field is generated to close the Hall current Our theory separates the Cowling channel into primary and secondary components

Original languageEnglish
Pages (from-to)6416-6425
Number of pages10
JournalJournal of Geophysical Research: Space Physics
Volume118
Issue number10
DOIs
Publication statusPublished - Oct 2013

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cowlings
Hall currents
field aligned currents
Ionosphere
Shear waves
magnetohydrodynamic waves
ionospheres
shears
S-wave
ionosphere
Electric fields
shear
Polarization
Magnetosphere
reflected waves
electric field
Parameterization
ionospherics
electric fields
electric field strength

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

Cite this

Theory of Cowling channel formation by reflection of shear Alfven waves from the auroral ionosphere. / Yoshikawa, A.; Amm, O.; Vanhamäki, H.; Nakamizo, A.; Fujii, R.

In: Journal of Geophysical Research: Space Physics, Vol. 118, No. 10, 10.2013, p. 6416-6425.

Research output: Contribution to journalArticle

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