Aspects of magnetosphere–ionosphere coupling in sawtooth substorms: a case study

Abstract

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 multispacecraft 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 magnetosphereionosphere (M-I) system during the initial transient phase of the substorm expansion.

Investigating the Development of Distinctive Subauroral Flow Channels During the November 7–8, 2004 Superstorm

“…Current diversion can enhance the R1‐R2 FACs and activate the SCW leading to intense SAPS flows (see details in Sections 1 and 3.5). Particularly in the presence of the HR region where the most intensive M‐I coupling takes place and where R1 FACs become enhanced (Sandholt et al., 2014).…”