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No evidence for externally triggered substorms based on superposed epoch analysis of IMF Bz

Freeman, Mervyn P.; Morley, S. K.. 2009 No evidence for externally triggered substorms based on superposed epoch analysis of IMF Bz. Geophysical Research Letters, 36 (21), L21101. 4, pp. 10.1029/2009GL040621

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Abstract/Summary

Superposed epoch analyses have shown that, on average, the interplanetary magnetic field (IMF) turns northward close to substorm onset. This has been commonly accepted as evidence for the substorm onset being triggered by a rapid northward turning of the IMF. Here we show that the tendency arises in any superposed epoch analysis of the IMF in which event onset is biased to occur for southward IMF, irrespective of a coincident rapid northward turning of the IMF. The overall IMF variation found in the largest superposed epoch analysis of this kind is also well reproduced using a Minimal Substorm Model in which substorm onsets are determined without the requirement of a northward IMF turning trigger. We discuss the explanation underlying these results and conclude that there is no conclusive evidence in favour of the hypothesis that substorm onsets are triggered by a rapid northward turning of the IMF. Citation: Freeman, M. P., and S. K. Morley (2009), No evidence for externally triggered substorms based on superposed epoch analysis of IMF B-z, Geophys. Res. Lett., 36, L21101, doi: 10.1029/2009GL040621.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1029/2009GL040621
Programmes: BAS Programmes > Polar Science for Planet Earth (2009 - ) > Environmental Change and Evolution
ISSN: 0094-8276
NORA Subject Terms: Atmospheric Sciences
Space Sciences
Date made live: 26 Oct 2010 10:46
URI: http://nora.nerc.ac.uk/id/eprint/10873

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