Field-aligned currents in the dayside cusp observed by Triad

TLDR

These field‑aligned currents are located poleward of the large‑scale region 1 currents reported by Iijima and Potemra (1976). Their characteristics at 800 km altitude over the northern hemisphere were determined from Triad satellite magnetometer data collected at College, Alaska, between January 1973 and October 1974. High‑latitude field‑aligned currents were observed mainly between 0930–1430 MLT at 78–80° invariant latitude during weakly disturbed conditions, flowing away from the ionosphere in the forenoon and into it in the afternoon, opposite to region 1 currents, with intensities rising under southward IMF and consistent with cusp‑related ionospheric currents, suggesting a significant coupling role between the interplanetary medium and the magnetosphere.

Abstract

The characteristics of field-aligned currents at an altitude of 800 km in the dayside high-latitude region over the northern hemisphere were determined from the Triad satellite magnetometer data recorded at College, Alaska, from January 1973 to October 1974. The field-aligned currents discussed here are located poleward of the large-scale field-aligned currents reported earlier and referred to as ‘region 1 field-aligned currents’ by the authors (Iijima and Potemra, 1976). These high-latitude field-aligned currents are most often observed in the dayside sector between 0930 and 1430 MLT and are statistically distributed between 78° and 80° invariant latitude during weakly disturbed conditions as indicated by westward electrojet activity (|AL| < 100 γ ). Although these high-latitude field-aligned currents show complicated variations, they generally flow away from the ionosphere in the forenoon hours (0930–1200 MLT) and into the ionosphere in the afternoon hours (1200–1430 MLT). These flow directions are opposite to the quasi-permanent region 1 field-aligned currents related to the Sqp currents previously discussed by the authors. The directions and spatial distribution of these high-latitude field-aligned currents are consistent with the antisolarward equivalent ionospheric current near 1200 MLT deduced from simultaneous ground-based magnetograms at ∼81° invariant latitude. The intensity of these high-latitude field-aligned currents increases as the interplanetary magnetic field increases in the southward direction. These field-aligned currents are located within the region associated with the dayside magnetospheric cusp, and their relationship to geomagnetic activity, especially interplanetary magnetic field variations, suggests that they may play an important role in the coupling between the interplanetary medium and the magnetosphere.