Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 32, 1277-1291, 2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Regular paper
20 Oct 2014
Aspects of magnetosphere–ionosphere coupling in sawtooth substorms: a case study
P. E. Sandholt1 and C. J. Farrugia2 1Department of Physics, University of Oslo, Oslo, Norway
2Space Science Center, University of New Hampshire, Durham, USA
Abstract. In a case study we report on repetitive substorm activity during storm time which was excited during Earth passage of an interplanetary coronal mass ejection (ICME) on 18 August 2003. Applying a combination of magnetosphere and ground observations during a favourable multi-spacecraft configuration in the plasma sheet (GOES-10 at geostationary altitude) and in the tail lobes (Geotail and Cluster-1), we monitor the temporal–spatial evolution of basic elements of the substorm current system. Emphasis is placed on activations of the large-scale substorm current wedge (SCW), spanning the 21:00–03:00 MLT sector of the near-Earth plasma sheet (GOES-10 data during the interval 06:00–12:00 UT), and magnetic perturbations in the tail lobes in relation to ground observations of auroral electrojets and convection in the polar cap ionosphere. The joint ground–satellite observations are interpreted in terms of sequential intensifications and expansions of the outer and inner current loops of the SCW and their respective associations with the westward electrojet centred near midnight (24:00 MLT) and the eastward electrojet observed at 14:00–15:00 MLT. Combined magnetic field observations across the tail lobe from Cluster and Geotail allow us to make estimates of enhancements of the cross-polar-cap potential (CPCP) amounting to ≈ 30–60 kV (lower limits), corresponding to monotonic increases of the PCN index by 1.5 to 3 mV m−1 from inductive electric field coupling in the magnetosphere–ionosphere (M–I) system during the initial transient phase of the substorm expansion.

Citation: Sandholt, P. E. and Farrugia, C. J.: Aspects of magnetosphere–ionosphere coupling in sawtooth substorms: a case study, Ann. Geophys., 32, 1277-1291,, 2014.
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