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Simultaneous Development of Multiple Auroral Substorms: Double Auroral Bulge Formation

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dc.contributor.authorOhtani, S.en
dc.contributor.authorGjerloev, J. W.en
dc.contributor.authorMcWilliams, K. A.en
dc.contributor.authorRuohoniemi, John M.en
dc.contributor.authorFrey, H. U.en
dc.contributor.departmentElectrical and Computer Engineeringen
dc.date.accessioned2021-07-29T12:47:02Zen
dc.date.available2021-07-29T12:47:02Zen
dc.date.issued2021-05en
dc.description.abstractThe expansion phase of auroral substorms is characterized by the formation of an auroral bulge, and it is generally considered that a single bulge forms following each substorm onset. However, we find that occasionally two auroral intensifications takes place close in time but apart in space leading to the formation of double auroral bulges, which later merge into one large bulge. We report three such events. In those events the westward auroral electrojet intensified in each auroral bulge, and geosynchronous magnetic field dipolarized in the same sector. It appears that two substorms took place simultaneously, and each substorm was accompanied by the formation of its own substorm current wedge system. This finding strongly suggests that the initiation of auroral substorms is a local process, and there is no global reference frame for their development. For example, ideas such as (i) the auroralbreakup takes place in the vicinity of the Harang reversal and (ii) the westward traveling surge maps to the interface between the plasma sheet and low-latitude boundary layer, do not necessarily hold for every substorm. Even if those ideas may be suggestive of causal magnetospheric processes, the reference structures themselves are probably not essential. It is also found that despite the formation of two distinct auroral bulges, the overall magnetosphere-ionosphere current system is represented by one globally coherent system, and we suggest that its structure is determined by the relative intensities and locations of the two substorm current wedges that correspond to the individual auroral bulges.en
dc.description.notesWe thank the Irish Meteorological Service for the Valentia magnetometer data, Danish Technical University Space for the Brorfelde magnetometer data, Lancaster University for the Borok magnetometer data, the Geological Survey of Canada for the Poste de-la-Baleine magnetometer data, the CARISMA network for the Pinawa magnetometer data, and the United States Geological Survey for the Boulder magnetometer data. We also gratefully acknowledge that the SuperMAG indices and polar maps of equivalent currents used in this study were derived from data provided by many organizations and institutes as listed at . We are also grateful to the OMNI initiative for the OMNI data and NOAA for the GOES magnetometer data. Support for this research at the Johns Hopkins University Applied Physics Laboratory was provided by National Aeronautics and Space Administration (NASA) grants NNX16AF74G (SO) and NNX16AG74G (SO), National Science Foundation (NSF) grants 1502700 (SO), 1603028 (SO), and 1417899 (JWG).en
dc.description.sponsorshipNational Aeronautics and Space Administration (NASA)National Aeronautics & Space Administration (NASA) [NNX16AF74G, NNX16AG74G]; National Science Foundation (NSF)National Science Foundation (NSF) [1502700, 1603028, 1417899]en
dc.description.versionPublished versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.doihttps://doi.org/10.1029/2020JA028883en
dc.identifier.eissn2169-9402en
dc.identifier.issn2169-9380en
dc.identifier.issue5en
dc.identifier.othere2020JA028883en
dc.identifier.urihttp://hdl.handle.net/10919/104435en
dc.identifier.volume126en
dc.language.isoenen
dc.rightsCreative Commons Attribution 4.0 Internationalen
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/en
dc.subjectauroral substormsen
dc.subjectauroral bulgesen
dc.subjectsubstorm current wedgeen
dc.subjectwestward auroral electrojeten
dc.subjectgeosynchronous dipolarizationen
dc.subjectHarang reversalen
dc.titleSimultaneous Development of Multiple Auroral Substorms: Double Auroral Bulge Formationen
dc.title.serialJournal of Geophysical Research-Space Physicsen
dc.typeArticle - Refereeden
dc.type.dcmitypeTexten
dc.type.dcmitypeStillImageen

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