Field-aligned current ordering and intense ground dB/dt variations

Xiangcheng Dong - UKRI-STFC; Malcolm Dunlop - UKRI-STFC, United Kingdom; Dong Wei - Beihang University, China; Junying Wang - Beihang University, China; Chao Xiong - GFZ, Germany

Session: Ground-Level Geomagnetically Induced Currents

Abstract

The orientation of field-aligned current sheets (FACs) can be inferred from dual-spacecraft correlations of the FAC signatures between two Swarm spacecraft (A and C), using the maximum correlations obtained from sliding data segments. Statistical analysis of both the correlations and the inferred orientations shows clear trends in magnetic local time (MLT) which reveal behaviour of both large and small scale currents. Individual events sampled by higher altitude spacecraft (e.g. the 4 Cluster spacecraft), in conjunction with Swarm also show two different domains of FACs: time variable, small-scale (10s km), and more stationary large-scale (>100 km) FACs. Comparable effects seen in the ground magnetometer signals (dH/dt) during storm/substorm activity and show similar distributions.  Intense dB/dt variations particularly take place in the main phase of a geomagnetic storm, particularly during  active substorms. The characteristics and response during the recovery phase of a geomagnetic storm were covered by multi-point ground and space measurements. The measurements show that corresponding signals in all measurements occur simultaneously (with suitable time lags) in this region. The most intense dB/dt (dH/dt) variations are associated with FACs corresponding to a modified SCW that are driven by BBFs at geosynchronous orbit around substorm onset.

​