Synthesis of various ionospheric convection patterns for IMF B y-dominated periods: Split crescent cells, exchange cells, and theta aurora formation

Masakazu Watanabe, George J. Soflco

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13 Citations (Scopus)

Abstract

When the dawn-to-dusk component of the interplanetary magnetic field (IMF BY) is dominant, ionospheric convection exhibits a distorted two-cell pattern with its dawn-dusk and interhemispheric asymmetries regulated by the IMF BY polarity. For BY > 0, the convection in the Northern (Southern) Hemisphere usually consists of a relatively round cell on the duskside (dawnside) and a crescent-shaped cell on the dawnside (duskside); for BY < 0, the dawn-dusk relationship is reversed. However, deviations from the basic round/crescent cell pattern are sometimes seen. Such nonstandard convection patterns include the dayside-enhanced crescent cell pattern, nightside-enhanced crescent cell pattern, split crescent cell pattern, and exchange cell pattern. Although at times the nonstandard convection patterns appear to be quite different from the basic round/crescent cell pattern, the underlying physical processes (i.e., the types of reconnection) and field line topologies are basically the same. We show that these various convection patterns can be synthesized by considering the topologies of magnetic field lines involved in eight types of reconnection. We also discuss the formation mechanism of the theta aurora configuration in terms of magnetic topology and ionospheric convection. The theta aurora configuration results from transient reconnection-driven convection when an IMF BY polarity switch reconfigures the exchange cell pattern. The bifurcation of the polar cap occurs as a consequence of accumulation of closed magnetic flux in the sunward return flow region of the round cell and intrusion of open magnetic flux into the "sub polar cap" that had been established by the primary exchange cell prior to the IMF change.

Original languageEnglish
Article numberA09218
JournalJournal of Geophysical Research: Space Physics
Volume113
Issue number9
DOIs
Publication statusPublished - Sep 1 2008
Externally publishedYes

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aurora
IMF
ionospherics
convection
synthesis
cells
topology
Topology
Magnetic flux
Magnetic fields
magnetic field
polar caps
magnetic fields
formation mechanism
bifurcation
magnetic flux
Convection
polarity
Southern Hemisphere
asymmetry

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

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abstract = "When the dawn-to-dusk component of the interplanetary magnetic field (IMF BY) is dominant, ionospheric convection exhibits a distorted two-cell pattern with its dawn-dusk and interhemispheric asymmetries regulated by the IMF BY polarity. For BY > 0, the convection in the Northern (Southern) Hemisphere usually consists of a relatively round cell on the duskside (dawnside) and a crescent-shaped cell on the dawnside (duskside); for BY < 0, the dawn-dusk relationship is reversed. However, deviations from the basic round/crescent cell pattern are sometimes seen. Such nonstandard convection patterns include the dayside-enhanced crescent cell pattern, nightside-enhanced crescent cell pattern, split crescent cell pattern, and exchange cell pattern. Although at times the nonstandard convection patterns appear to be quite different from the basic round/crescent cell pattern, the underlying physical processes (i.e., the types of reconnection) and field line topologies are basically the same. We show that these various convection patterns can be synthesized by considering the topologies of magnetic field lines involved in eight types of reconnection. We also discuss the formation mechanism of the theta aurora configuration in terms of magnetic topology and ionospheric convection. The theta aurora configuration results from transient reconnection-driven convection when an IMF BY polarity switch reconfigures the exchange cell pattern. The bifurcation of the polar cap occurs as a consequence of accumulation of closed magnetic flux in the sunward return flow region of the round cell and intrusion of open magnetic flux into the {"}sub polar cap{"} that had been established by the primary exchange cell prior to the IMF change.",
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