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In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge
Author(s) -
Forsyth C.,
Fazakerley A. N.,
Rae I. J.,
J. Watt C. E.,
Murphy K.,
Wild J. A.,
Karlsson T.,
Mutel R.,
Owen C. J.,
Ergun R.,
Masson A.,
Berthomier M.,
Donovan E.,
Frey H. U.,
Matzka J.,
Stolle C.,
Zhang Y.
Publication year - 2014
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2013ja019302
Subject(s) - substorm , geophysics , current (fluid) , electrojet , ionosphere , earth's magnetic field , azimuth , substructure , cluster (spacecraft) , geology , physics , magnetosphere , magnetic field , astronomy , oceanography , structural engineering , quantum mechanics , computer science , engineering , programming language
The substorm current wedge (SCW) is a fundamental component of geomagnetic substorms. Models tend to describe the SCW as a simple line current flowing into the ionosphere toward dawn and out of the ionosphere toward dusk, linked by a westward electrojet. We use multispacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 January 2010, in conjunction with ground‐based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft traveled east‐west azimuthally above the auroral region. We show that the SCW has significant azimuthal substructure on scales of 100 km at altitudes of 4000–7000 km. We identify 26 individual current sheets in the Cluster 4 data and 34 individual current sheets in the Cluster 1 data, with Cluster 1 passing through the SCW 120–240 s after Cluster 4 at 1300–2000 km higher altitude. Both spacecraft observed large‐scale regions of net upward and downward field‐aligned current, consistent with the large‐scale characteristics of the SCW, although sheets of oppositely directed currents were observed within both regions. We show that the majority of these current sheets were closely aligned to a north‐south direction, in contrast to the expected east‐west orientation of the preonset aurora. Comparing our results with observations of the field‐aligned current associated with bursty bulk flows (BBFs), we conclude that significant questions remain for the explanation of SCW structuring by BBF‐driven “wedgelets.” Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the SCW.