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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 8
Ann. Geophys., 18, 897–907, 2000
© European Geosciences Union 2000
Ann. Geophys., 18, 897–907, 2000
© European Geosciences Union 2000

  31 Aug 2000

31 Aug 2000

Interhemispheric observations of nightside ionospheric electric fields in response to IMF Bz and By changes and substorm pseudobreakup

T. K. Yeoman1, R. V. Lewis2, H. Khan1, S. W. H. Cowley1, and J. M. Ruohoniemi3 T. K. Yeoman et al.
  • 1Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
  • 2Ipswich School, Henley Road, Ipswich, Suffolk, IP1 3SG, UK
  • 3Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20707, USA
  • Correspondence to: T. K. Yeoman
  • e-mail:

Abstract. HF radar data during equinoctial, small IMF By conditions have enabled the ionospheric convection during the substorm growth phase and substorm pseudobreakup to be studied in both hemispheres. This has revealed both conjugate and non-conjugate convection behaviour during the substorm growth phase before and after the pseudobreakup onset. The nightside convection pattern is found to respond promptly to the southward turning of the interplanetary magnetic field (IMF) which impacts on the dusk flank of the magnetosphere due to an inclined phase front in the IMF in the case study presented. The subsequent interhemispheric observations of nightside convection are controlled by the IMF By polarity. The time scale for the response to changes in the IMF By component is found to be a little longer than for Bz, and the full impact of the IMF By is not apparent in the nightside convection until after substorm pseudobreakup has occurred. The pseudobreakup itself is found to result in a transitory suppression in the ionospheric electric field in both hemispheres. This flow suppression is very similar to that observed in HF radar observations of full substorm onset, with the exception of a lack of subsequent poleward expansion.

Key words: Ionosphere (auroral ionosphere) - Magnetospheric physics (magnetosphere-ionosphere interactions; storms and substorms)

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