Pc3 pulsations in the polar cap and at low latitude

Abstract

We present a statistical analysis of Pc3–4 pulsations during 2005 at two polar cap stations (Terra Nova Bay and Dome C, Antarctica) and, for comparison, at a low‐latitude station (L’Aquila). The analysis technique allows to discriminate the signal component from the background noise in the power spectrum and to determine the frequency of such ULF signal, commonly associated to the upstream wave source. The comparison of data makes evident that the characteristics of the ULF pulsations are different at low and high latitudes, and significant differences emerge also between the two polar cap stations. At Dome C the ULF signals are observed during the whole day, while at Terra Nova Bay and at L’Aquila the signals are mainly observed in the dayside sector. The different cone angle dependence at L’Aquila and Dome C, the steeper slope in the frequency dependence on the interplanetary magnetic field strength at Dome C with respect to L’Aquila and Terra Nova Bay and the time dependence of the coherence between pulsations at the Antarctic stations suggest that at low‐latitude waves are transmitted to the ground from a region close to the subsolar bow shock, while near the geomagnetic pole waves are mainly transmitted through the magnetotail lobes. At Terra Nova Bay, where the local field lines approach the cusp around noon and are stretched into the magnetotail around midnight, the transmission path seems to be time dependent, with daytime and nighttime pulsations penetrating through the subsolar point and via the magnetotail lobes, respectively.