Low and mid-frequency pulsations in the polar cap: polarization pattern and MLT dependence of the spectral power during the descending phase of the solar cycle

Abstract

We present a statistical analysis of ULF (1-100 mHz) geomagnetic measurements conducted during years 2003-<br />2006 at the Italian/French base of Concordia at Dome C, close to the geomagnetic pole, and at the Italian base<br />«Mario Zucchelli» at Terra Nova Bay, also located in the polar cap, but at lower latitude. Our analysis shows that<br />high latitude ULF pulsation power is largely controlled by the solar wind speed. At Terra Nova Bay the power<br />shows a maximum at local noon, clearly related to cusp and closed field lines phenomena. At few mHz, the polarization<br />pattern indicates field line resonances driven, just equatorward with respect to the station, by waves<br />propagating tailward; the polarization of higher frequency pulsations, mostly originated from interplanetary upstream<br />waves, suggests waves propagating sunward from the night sector. At Dome C the wave power shows a<br />small enhancement in the local morning, more pronounced for mid-frequency pulsations; the polarization pattern,<br />at all frequencies, appears to indicate waves propagating sunward from the night sector, suggesting a propagation<br />channel to the ground via the magnetotail lobes.

Keywords

• ULF waves – Antarctica – Geomagnetic pulsations – Polarization pattern – upstream waves