Modulation of the Substorm Current Wedge by Bursty Bulk Flows: September 8, 2002 - Revisited

Palin, Laurianne and Opgenoorth, Hermann and Ågren, Karin and Zivkovic, Tatjana and Sergeev, Victor and Facskó, Gábor István (2016) Modulation of the Substorm Current Wedge by Bursty Bulk Flows: September 8, 2002 - Revisited. JOURNAL OF GEOPHYSICAL RESEARCH: SPACE PHYSICS, 121. pp. 4466-4482. ISSN 2169-9380

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Abstract

The ultimate formation mechanism of the substorm current wedge (SCW) remains to-date unclear. In this study, we investigate its relationship to plasma flows at substorm onset and throughout the following expansion phase. We revisit the case of September 8, 2002, which has been defined as "the best textbook example for a localized substorm onset observation" because of its excellent coverage by both spacecraft in the magnetotail and ground-based observatories is revisited. We found that a dense sequence of arrival of nightside flux transfer events (which can be understood as the lobe magnetic signature due to a bursty bulk flow travelling earthward in the central plasmasheet) in the near-Earth tail leads to a modulation (and further step-like built-up) of the SCW intensity during the substorm expansion phase. In addition, we found that small SCWs are created also during the growth phase of the event in association with another less intense sequence of NFTEs. The differences between the sequence of NFTEs in the growth and expansion phase are discussed. We conclude that the envelope of the magnetic disturbances which we typically refer to as an intense magnetic substorm is the result of a group or sequence of more intense and more frequent NFTEs.

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