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Final published version
Licence: CC BY
Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge
AU - Forsyth, C.
AU - Fazakerley, A. N.
AU - Rae, I.J.
AU - Watt, C. E. J.
AU - Murphy, Kyle R.
AU - Wild, Jim
AU - Karlsson, T.
AU - Mutel, Robert
AU - Owen, C. J.
AU - Ergun, Robert
AU - Masson, A.
AU - Berthomier, M.
AU - Donovan, E.
AU - Frey, H. U.
AU - Matzka, Juergen
AU - Stolle, C.
AU - Zhang, Y.
N1 - This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
PY - 2014/2/12
Y1 - 2014/2/12
N2 - 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 towards dawn and out of the ionosphere towards dusk, linked by a westward electrojet. We use multi-spacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 Jan 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft travelled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal sub-structure on scales of 100~km at altitudes of 4,000-7,000~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 1,300-2,000~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 pre-onset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs) we conclude that the structuring of the SCW cannot solely be due to BBF driven "wedgelets". Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the SCW.
AB - 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 towards dawn and out of the ionosphere towards dusk, linked by a westward electrojet. We use multi-spacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 Jan 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft travelled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal sub-structure on scales of 100~km at altitudes of 4,000-7,000~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 1,300-2,000~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 pre-onset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs) we conclude that the structuring of the SCW cannot solely be due to BBF driven "wedgelets". Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the SCW.
KW - Substorm current wedge
KW - Field-aligned current
KW - Wedgelets
KW - Aurora
KW - Magnetosphere
KW - Earth
U2 - 10.1002/2013JA019302
DO - 10.1002/2013JA019302
M3 - Journal article
VL - 119
SP - 927
EP - 946
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
SN - 2169-9402
IS - 2
ER -