On the relationship between morning sector irregular magnetic pulsations and field aligned currents

Abstract

Data from search coil magnetometer, riometer, and photometer instrumentation at Siple, Antarctica, are compared with vector magnetometer data from south polar passes of the MAGSAT satellite for three magnetically disturbed days in early 1980. Two kinds of association were found between irregular pulsation activity in the 0.5‐ to 40‐s frequency band (Pi 1) observed on the ground and magnetospheric‐ionospheric currents measured from space. (1) During each MAGSAT polar pass in the morning sector the level of Pi 1 activity correlates well with the intensities of three‐dimensional current systems. Fine structure was often observed in the field‐aligned currents during periods of intense Pi activity. Birkeland currents include 2‐ to 10‐s (16–80 km) structured perturbations evident in the transverse components of the field, most likely indicating filamentary currents. (2) The pulsations observed at Siple in the morning sector include an asymmetric class of fluctuations in dB/dt whenever the region 2 field‐aligned currents extend to or equatorward of the invariant latitude of Siple and do not have such components when the currents do not extend to that latitude. These observations support models suggesting that Pi 1 pulsations represent fluctuations of a three‐dimensional current system in the magnetosphere and are consistent with recent conductivity and current enhancement models for the ionospheric source of Pi 1 activity.