Detailed correlations of magnetic field and riometer observations at L = 4.2 with pulsating aurora

Abstract

Pi 1 magnetic pulsations in the period range 5–15 s recorded on the ground at L = 4.2 during pulsating aurora are studied via the use of data collected at Siple Station, Antarctica, during 1979. Pulsating aurora exceeding 200 R of 4278‐Å emission occurred for approximately 5% of the 1400 hours of photometer operation and was always accompanied by ULF waves. A striking characteristic of the ULF waves is a strong westward component in dB/dt during the auroral light bursts. A detailed correlation of the ULF waves with riometer and flux gate magnetic field data reveal that the magnetic field variations were very closely correlated with D region cosmic noise absorption. Asymmetric pulsations result from the slow recovery of the magnetic field and occurred when the auroral light pulses were of short duration. We conclude from this study that the ground Pi 1 recorded during pulsating aurora at L = 4.2 were due to an overhead current system produced by the particle precipitation. The characteristic westward component in dB/dt could be interpreted as being due to an equatorially directed local ionospheric current driven by a polarization electric field. One must conclude from the results of this paper that the Pi 1 waves studied had no role in the mechanism that precipitated the particles responsible for the pulsating aurora at L = 4.2.