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

Morley, S.K.; Freeman, M.P. ORCID: https://orcid.org/0000-0002-8653-8279. 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 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/3113

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