Filamentary field-aligned currents at the polar cap region during northward interplanetary magnetic field derived with the Swarm constellation.

Jan Rauberg,Simon Wing,Haje Korth,Guram Kervalishvili,Hermann Lühr,Tao Huang

doi:10.5194/angeo-34-901-2016

Abstract

ESA’s Swarm constellation mission makes it possible for the first time to determine field-aligned currents (FACs) in the ionosphere uniquely. In particular at high latitudes, the dual-satellite approach can reliably detect some FAC structures which are missed by the traditional single-satellite technique. These FAC events occur preferentially poleward of the auroral oval and during times of northward interplanetary magnetic field (IMF) orientation. Most events appear on the nightside. They are not related to the typical FAC structures poleward of the cusp, commonly termed NBZ. Simultaneously observed precipitating particle spectrograms and auroral images from Defense Meteorological Satellite Program (DMSP) satellites are consistent with the detected FACs and indicate that they occur on closed field lines mostly adjacent to the auroral oval. We suggest that the FACs are associated with Sun-aligned filamentary auroral arcs. Here we introduce in an initial study features of the high-latitude FAC structures which have been observed during the early phase of the Swarm mission. A more systematic survey over longer times is required to fully characterize the so far undetected field aligned currents.

Highlights

The high-latitude region close to the geomagnetic pole is commonly termed “polar cap”
The Swarm constellation of satellites provides the opportunity of improved field-aligned current (FAC) observations
Previous missions have obviously missed a good part of FAC features

Summary

Introduction

The high-latitude region close to the geomagnetic pole is commonly termed “polar cap”. In the case of IMF Bx dependence, a dominant positive, Sun-pointing component supports stronger FAC intensity in the Southern Hemisphere, due to anti-parallel orientations of IMF and southern lope field lines. This favors magnetic merging in the Southern Hemisphere (e.g., Fairfield and Scudder, 1985). Relatively few papers focus on observed field-aligned current distributions (e.g., Korth et al, 2004, 2005; Vennerstroem et al, 2005) This is probably due to the fact that FACs in this region have variable current geometries and cannot be estimated from single-satellite magnetic field measurements.

Swarm mission and field-aligned current estimate

Solar-wind and interplanetary magnetic field data

Observations

Field-aligned currents at high latitude

Sep 2014 30 Aug 2014 15 Sep 2014 23 Dec 2014 23 Dec 2014 4 Dec 2014

Complementary observations during events

Discussion

Prevailing conditions during high-latitude FACs

Comparison with AMPERE

Summary