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Field line resonances as a trigger and a tracer for substorm onset

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  • In this paper, we show that periodic auroral arc structures are seen at the location of one particular auroral substorm onset for the 15 min preceding onset, suggesting that field line resonances should be considered a strong candidate for triggering substorm onset. Irrespective of whether this field line resonance is coincidentally or causally linked to this substorm onset, the characteristics of the field line resonance can be used to remote sense the characteristics of the geomagnetic field line that supports substorm onset. In this instance, the eigenfrequency of this resonance is around 12 mHz. Interestingly, however, there is no evidence of this field line resonance in a seven satellite major Time History of Events and Macroscale Interactions during Substorms (THEMIS)-GOES conjunction, ranging from geosynchronous orbit to similar to 30 R-E. However, using space-based cross-phase measurements of the local field line eigenfrequency at the inner THEMIS locations, we find that the local field line eigenfrequency is 6-10 mHz. Hence, we can reliably say that this 12 mHz Field Line Resonance (FLR) must lie inside of THEMIS locations. Our conclusion is that a high-mfield line resonance can both represent a strong candidate for a trigger for substorm onset, as first proposed by Samson et al. (1992), and that its characteristics can provide invaluable information as to where substormonset occurs in the magnetosphere.

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    Article (Published)
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    © 2014 American Geophysical Union. This version of this article is open access and can be downloaded and shared. The original author(s) and source must be cited.
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    • Rae, I. Johnathan, Murphy, K. R., Watt, Clare E. J., Rostoker, Gordon, Rankin, Robert, Mann, Ian R., Hodgson, Cory R., Frey, Harald U., Degeling, Alex W., & Forsyth, Colin. (2014). Field line resonances as a trigger and a tracer for substorm onset. Journal of Geophysical Research: Space Physics, 119(7), 5343-5363.
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