Timing and localization of ionospheric signatures associated with substorm expansion phase onset

Rae, I. J., Mann, I. R., Murphy, K. R., Milling, D. K., Parent, A., Angelopoulos, V., Frey, H. U., Kale, A., Watt, C. E. J., Mende, S. B. and Russell, C. T. (2009) Timing and localization of ionospheric signatures associated with substorm expansion phase onset. Journal of Geophysical Research, 114. A00C09. ISSN 0148-0227 doi: 10.1029/2008JA013559

Abstract/Summary

In this paper, we present case studies of the optical and magnetic signatures of the characteristics of the first minute of substorm expansion phase onset observed in the ionosphere. We find that for two isolated substorms, the onset of magnetic pulsations in the 24–96 s period wavelet band are colocated in time and space with the formation and development of small-scale optical undulations along the most equatorward preexisting auroral arc prior to auroral breakup. These undulations undergo an inverse spatial cascade into vortices prior to the release of the westward traveling surge. We also present a case study of a multiple activation substorm, whereby discrete onsets of ULF wave power above a predetermined quiet time threshold are shown to be associated with specific optical intensifications and brightenings. Moreover, in the multiple activation substorm event, we show that neither the formation of the small-scale undulations nor the formation of similar structures along a north–south aligned arc is sufficient to produce auroral breakup associated with expansion phase onset. It is only ∼10 min after these two disparate activation regions initiate that auroral breakup and the subsequent formation of a westward traveling surge occur. We discuss the implications of these results in terms of the triggering mechanisms likely to be occurring during these specific events.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/32825
Identification Number/DOI	10.1029/2008JA013559
Refereed	Yes
Divisions	No Reading authors. Back catalogue items Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Uncontrolled Keywords	substorm; ULF waves; THEMIS
Publisher	American Geophysical Union
Download/View statistics	View download statistics for this item