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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 12
Ann. Geophys., 24, 3365–3381, 2006
https://doi.org/10.5194/angeo-24-3365-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 3365–3381, 2006
https://doi.org/10.5194/angeo-24-3365-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  21 Dec 2006

21 Dec 2006

Towards a synthesis of substorm electrodynamics: HF radar and auroral observations

A. Grocott1, M. Lester1, M. L. Parkinson2, T. K. Yeoman1, P. L. Dyson2, J. C. Devlin3, and H. U. Frey4 A. Grocott et al.
  • 1Department of Physics {&} Astronomy, University of Leicester, Leicester LE1 7RH, UK
  • 2Department of Physics, La Trobe University, Victoria 3086, Australia
  • 3Department of Electronic Engineering, La Trobe University, Victoria 3086, Australia
  • 4Space Sciences Laboratory, University of California Berkeley, Berkeley, CA 94720, USA

Abstract. At 08:35 UT on 21 November 2004, the onset of an interval of substorm activity was captured in the southern hemisphere by the Far UltraViolet (FUV) instrument on board the IMAGE spacecraft. This was accompanied by the onset of Pi2 activity and subsequent magnetic bays, evident in ground magnetic data from both hemispheres. Further intensifications were then observed in both the auroral and ground magnetic data over the following ~3 h. During this interval the fields-of-view of the two southern hemisphere Tasman International Geospace Enviroment Radars (TIGER) moved through the evening sector towards midnight. Whilst initially low, the amount of backscatter from TIGER increased considerably during the early stages of the expansion phase such that by ~09:20 UT an enhanced dusk flow cell was clearly evident. During the expansion phase the equatorward portion of this flow cell developed into a narrow high-speed flow channel, indicative of the auroral and sub-auroral flows identified in previous studies (e.g. Freeman et al., 1992; Parkinson et al., 2003). At the same time, higher latitude transient flow features were observed and as the interval progressed the flow reversal region and Harang discontinuity became very well defined. Overall, this study has enabled the spatial and temporal development of many different elements of the substorm process to be resolved and placed within a simple conceptual framework of magnetospheric convection. Specifically, the detailed observations of ionospheric flows have illustrated the complex interplay between substorm electric fields and associated auroral dynamics. They have helped define the distinct nature of different substorm current systems such as the traditional substorm current wedge and the more equatorward currents associated with polarisation electric fields. Additionally, they have revealed a radar signature of nightside reconnection which provides the promise of quantifying nightside reconnection in a way which has already proved extremely successful in studies of the dayside magnetosphere.

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