The ionospheric response to interplanetary magnetic field variations: Evidence for rapid global change and the role of preconditioning in the magnetosphere

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Abstract

We have found observational evidence for a rapid communication of interplanetary magnetic field (IMF) changes to the global ionosphere and evidence for the state of the magnetosphere in the previous hour conditioning this response. These conclusions are drawn from a case study of sunward flow bursts on the nightside polar cap boundary observed by geomagnetically conjugate HF radars. The flow burst excitation consists of two factors: (1) At the time of the flow burst, the magnetosphere still held a memory of the stable and northward IMF period that had persisted up until 1 hour before the flow burst (internal condition). During the northward IMF period a theta aurora associated with a sunward flow channel was formed in the polar cap. After that the IMF turned southward, and the transpolar arc decayed antisunward. However, by the time of the flow burst (i.e., 1 hour after the IMF southward turning), the Sun-aligned arc had not yet completely vanished, and in the poleward expanded portion of the northern plasma sheet, there was still a remnant of the sunward flow channel susceptive to an external forcing. (2) One hour after the southward turning of the IMF a sharp IMF transition from southward to northward BZ impinged on the dayside magnetopause (external condition). On arriving at the dayside cusp ionosphere the BZ transition signal pervaded the entire polar cap ionosphere instantaneously (<1 min) and reached the nightside plasma sheet. There, the remnant of the sunward flow channel was reactivated by the BZ transition, and a sunward flow burst was observed first in the northern ionosphere and then in the southern ionosphere with a 7-min time delay. Thus the sunward flow burst represents a rapid global response of the ionosphere starting 2-3 min after the IMF change at the subsolar magnetopause.

Original languageEnglish
Article number1999JA000433
Pages (from-to)22955-22977
Number of pages23
JournalJournal of Geophysical Research: Space Physics
Volume105
Issue numberA10
Publication statusPublished - Jan 1 2000
Externally publishedYes

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Magnetosphere
preconditioning
interplanetary magnetic fields
magnetic fields
global change
magnetospheres
ionospherics
magnetosphere
Ionosphere
bursts
Magnetic fields
ionospheres
magnetic field
ionosphere
polar caps
channel flow
Magnetopause
Channel flow
magnetopause
arcs

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  • 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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title = "The ionospheric response to interplanetary magnetic field variations: Evidence for rapid global change and the role of preconditioning in the magnetosphere",
abstract = "We have found observational evidence for a rapid communication of interplanetary magnetic field (IMF) changes to the global ionosphere and evidence for the state of the magnetosphere in the previous hour conditioning this response. These conclusions are drawn from a case study of sunward flow bursts on the nightside polar cap boundary observed by geomagnetically conjugate HF radars. The flow burst excitation consists of two factors: (1) At the time of the flow burst, the magnetosphere still held a memory of the stable and northward IMF period that had persisted up until 1 hour before the flow burst (internal condition). During the northward IMF period a theta aurora associated with a sunward flow channel was formed in the polar cap. After that the IMF turned southward, and the transpolar arc decayed antisunward. However, by the time of the flow burst (i.e., 1 hour after the IMF southward turning), the Sun-aligned arc had not yet completely vanished, and in the poleward expanded portion of the northern plasma sheet, there was still a remnant of the sunward flow channel susceptive to an external forcing. (2) One hour after the southward turning of the IMF a sharp IMF transition from southward to northward BZ impinged on the dayside magnetopause (external condition). On arriving at the dayside cusp ionosphere the BZ transition signal pervaded the entire polar cap ionosphere instantaneously (<1 min) and reached the nightside plasma sheet. There, the remnant of the sunward flow channel was reactivated by the BZ transition, and a sunward flow burst was observed first in the northern ionosphere and then in the southern ionosphere with a 7-min time delay. Thus the sunward flow burst represents a rapid global response of the ionosphere starting 2-3 min after the IMF change at the subsolar magnetopause.",
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N2 - We have found observational evidence for a rapid communication of interplanetary magnetic field (IMF) changes to the global ionosphere and evidence for the state of the magnetosphere in the previous hour conditioning this response. These conclusions are drawn from a case study of sunward flow bursts on the nightside polar cap boundary observed by geomagnetically conjugate HF radars. The flow burst excitation consists of two factors: (1) At the time of the flow burst, the magnetosphere still held a memory of the stable and northward IMF period that had persisted up until 1 hour before the flow burst (internal condition). During the northward IMF period a theta aurora associated with a sunward flow channel was formed in the polar cap. After that the IMF turned southward, and the transpolar arc decayed antisunward. However, by the time of the flow burst (i.e., 1 hour after the IMF southward turning), the Sun-aligned arc had not yet completely vanished, and in the poleward expanded portion of the northern plasma sheet, there was still a remnant of the sunward flow channel susceptive to an external forcing. (2) One hour after the southward turning of the IMF a sharp IMF transition from southward to northward BZ impinged on the dayside magnetopause (external condition). On arriving at the dayside cusp ionosphere the BZ transition signal pervaded the entire polar cap ionosphere instantaneously (<1 min) and reached the nightside plasma sheet. There, the remnant of the sunward flow channel was reactivated by the BZ transition, and a sunward flow burst was observed first in the northern ionosphere and then in the southern ionosphere with a 7-min time delay. Thus the sunward flow burst represents a rapid global response of the ionosphere starting 2-3 min after the IMF change at the subsolar magnetopause.

AB - We have found observational evidence for a rapid communication of interplanetary magnetic field (IMF) changes to the global ionosphere and evidence for the state of the magnetosphere in the previous hour conditioning this response. These conclusions are drawn from a case study of sunward flow bursts on the nightside polar cap boundary observed by geomagnetically conjugate HF radars. The flow burst excitation consists of two factors: (1) At the time of the flow burst, the magnetosphere still held a memory of the stable and northward IMF period that had persisted up until 1 hour before the flow burst (internal condition). During the northward IMF period a theta aurora associated with a sunward flow channel was formed in the polar cap. After that the IMF turned southward, and the transpolar arc decayed antisunward. However, by the time of the flow burst (i.e., 1 hour after the IMF southward turning), the Sun-aligned arc had not yet completely vanished, and in the poleward expanded portion of the northern plasma sheet, there was still a remnant of the sunward flow channel susceptive to an external forcing. (2) One hour after the southward turning of the IMF a sharp IMF transition from southward to northward BZ impinged on the dayside magnetopause (external condition). On arriving at the dayside cusp ionosphere the BZ transition signal pervaded the entire polar cap ionosphere instantaneously (<1 min) and reached the nightside plasma sheet. There, the remnant of the sunward flow channel was reactivated by the BZ transition, and a sunward flow burst was observed first in the northern ionosphere and then in the southern ionosphere with a 7-min time delay. Thus the sunward flow burst represents a rapid global response of the ionosphere starting 2-3 min after the IMF change at the subsolar magnetopause.

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