In situ spatio-temporal measurements of the detailed azimuthal substructure of the substorm current wedge
Thursday, 26 May 2016
Colin Forsyth1, Andrew Neil Fazakerley1, Jonathan Rae1, Clare Watt2, Kyle R Murphy3, James A Wild4, Tomas Karlsson5, Robert L Mutel6, Christopher John Owen1, Robert E Ergun7, Arnaud Masson8, Matthieu Berthomier9, Eric Donovan10, Harald U Frey11, Juergen Matzka12, Claudia Stolle13, Yongliang Zhang14 and Licia C Ray15, (1)University College London, London, United Kingdom, (2)University of Reading, Reading, United Kingdom, (3)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (4)University of Lancaster, Lancaster, United Kingdom, (5)KTH Royal Institute of Technology, Stockholm, Sweden, (6)University of Iowa, Iowa City, IA, United States, (7)University of Colorado, Laboratory for Atmospheric and Space Research, Boulder, CO, United States, (8)European Space Agency, SRE-O, Villanueva De La Can, Spain, (9)Laboratoire de Physique des Plasmas, Saint-Maur Des Fossés Cedex, France, (10)University of Calgary, Calgary, AB, Canada, (11)University of California Berkeley, Berkeley, CA, United States, (12)Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany, (13)Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany, (14)Johns Hopkins University, Baltimore, MD, United States, (15)Mullard Space Science Laboratory, Dorking, RH5, United Kingdom
Abstract:
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.
