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On the association between northward turnings of the interplanetary magnetic field and substorm onsets

Morley, S.K.; Freeman, M.P.. 2007 On the association between northward turnings of the interplanetary magnetic field and substorm onsets. Geophysical Research Letters, 34 (8), L08104. 6, pp. 10.1029/2006GL028891

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Abstract/Summary

We re-examine whether substorms are triggered by solar wind fluctuations or an internal magnetospheric instability by comparing the statistical associations between substorm onsets and (1) an external trigger definition, (2) a simple internal trigger definition of only prior loading of solar wind energy that is a subset of the external trigger definition. Statistical associations are calculated both for observed substorm onsets and onsets generated by a Minimal Substorm Model in which substorms are purely internally triggered. Thence we argue that a minimum interval of prior loading is a necessary condition for substorm onset, a subsequent northward IMF turning is not necessary, and consequently that an internal trigger from a magnetospheric instability is a necessary and sufficient condition for substorm onset. We discuss how this result may explain a report that externally triggered substorms are systematically larger than non-externally triggered substorms.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1029/2006GL028891
Programmes: BAS Programmes > Global Science in the Antarctic Context (2005-2009) > Natural Complexity Programme
ISSN: 0094-8276
Additional Keywords: IMF; substorm; triggering
NORA Subject Terms: Space Sciences
Date made live: 27 May 2008 10:29
URI: http://nora.nerc.ac.uk/id/eprint/3113

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