Greater than 0.1‐Hz ULF magnetic pulsations measured at South Pole, Antarctica

Abstract

South Pole pulsation activity at frequencies greater than 0.1‐Hz is analyzed in this study and found to consist predominantly of large‐amplitude, irregular pulsations (Pi 1) closely correlated with overhead auroral activity. These pulsations therefore have two diurnal maxima related to the substorm polar expansion nightside aurora and cusp or dayside aurora. The dependence of this magnetic nightside Pi activity at South Pole on Kp and interplanetary magnetic field parameters is consistent with a strong substorm correlation. As found at lower latitudes, when pulsating aurora is evident in the photometric data there can be a good detailed correlation between the auroral luminosity fluctuations and the magnetic pulsations, suggesting that the pulsations are locally produced by overhead currents driven by the particle precipitation. Nightside Pi activity is often of larger‐amplitude than the dayside Pi and appears in bursts of pulsations having 5 to 20 minsduration. The burst‐like character arises because of the rapid poleward expansion of discrete auroral forms from the nightside auroral oval, as is evident in the South Pole photometric data. South Pole nightside auroral magnetic pulsations generally commence well after the onset of similar auroral magnetic pulsations recorded at Siple, Antarctica, a subauroral location. One third of the hours during which structured, band‐limited pulsations (Pc 1) are observed at the low‐latitude, Siple, Antarctica, location also contain Pc 1 observed at South Pole. When it is possible to identify similar structures in Pc 1 between South Pole and Siple they are in phase, in contrast to out of phase structures for opposite hemisphere stations. This supports horizontal ducting of Pc 1 from lower‐latitudes to South Pole. However, there often appears much more structure at South Pole than recorded at Siple, suggesting many paths of horizontal propagation from multiple lower‐latitude sources if the signals are not generated on South Pole field lines. The pronounced inverse correlation of South Pole Pc 1 with magnetic activity means that the magnetic field topology and/or ionospheric conditions associated with substorm activity preclude the possible propagation of Pc 1 to South Pole from lower‐latitudes when the magnetic activity is high.