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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 27, issue 2
Ann. Geophys., 27, 659–668, 2009
https://doi.org/10.5194/angeo-27-659-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 27, 659–668, 2009
https://doi.org/10.5194/angeo-27-659-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  11 Feb 2009

11 Feb 2009

A superposed epoch analysis of auroral evolution during substorm growth, onset and recovery: open magnetic flux control of substorm intensity

S. E. Milan1, A. Grocott1, C. Forsyth1,2, S. M. Imber1,3, P. D. Boakes1,4, and B. Hubert5 S. E. Milan et al.
  • 1Department of Physics and Astronomy, University of Leicester, Leicester, UK
  • 2Mullard Space Sciences Laboratory, University College London, Surrey, UK
  • 3Heliophysics Division, NASA GSFC, Greenbelt, MD, USA
  • 4British Antarctic Survey, Natural Environment Research Council, High Cross, Cambridge, UK
  • 5Laboratory of Planetary and Atmospheric Physics, University of Liege, Liege, Belgium

Abstract. We perform two superposed epoch analyses of the auroral evolution during substorms using the FUV instrument on the Imager for Magnetopause-to-Aurora Global Explorer (IMAGE) spacecraft. The larger of the two studies includes nearly 2000 substorms. We subdivide the substorms by onset latitude, a measure of the open magnetic flux in the magnetosphere, and determine average auroral images before and after substorm onset, for both electron and proton aurora. Our results indicate that substorms are more intense in terms of auroral brightness when the open flux content of the magnetosphere is larger, and that magnetic flux closure is more significant. The increase in auroral brightness at onset is larger for electrons than protons. We also show that there is a dawn-dusk offset in the location of the electron and proton aurora that mirrors the relative locations of the region 1 and region 2 current systems. Superposed epoch analyses of the solar wind, interplanetary magnetic field, and geomagnetic indices for the substorms under study indicate that dayside reconnection is expected to occur at a faster rate prior to low latitude onsets, but also that the ring current is enhanced for these events.

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