ULF geomagnetic pulsations in the southern polar cap: Simultaneous measurements near the cusp and the geomagnetic pole

摘要

During November 2003, a 1-week test campaign of ULF geomagnetic field measurements was conducted at the new Italian/French base of Concordia (Dome C, Antarctic plateau), close to the geomagnetic pole, at a corrected geomagnetic latitude of ～89°S. An analysis of these measurements is presented, together with a comparison with simultaneous measurements conducted at the Italian “Mario Zucchelli” base, at Terra Nova Bay, also located in the polar cap, but at lower latitude (～80°S). The variable solar wind and interplanetary magnetic field conditions made it possible to monitor the Pc 3–4 ULF pulsation activity under different magnetospheric conditions. For quiet conditions, the pulsation power does not show evidence for a diurnal modulation at Dome C, while at Terra Nova Bay it maximizes around local magnetic noon. This result can be interpreted in terms of the different latitude of the two stations which might be linked to different magnetospheric regions: Dome C deep in the polar cap, and Terra Nova Bay approaching the cusp around noon. Conversely, during a strong geomagnetic storm, the wave activity at the two stations becomes very similar, and major ground manifestations are driven by strong solar wind pressure pulses. The clear dependence of the pulsation frequency with the interplanetary magnetic field strength suggests that upstream waves can be the source of pulsations not only at Terra Nova Bay but also at Dome C, in the deep polar cap. We also find a clear relationship between the pulsation power and the solar wind speed which is more pronounced at Dome C, where cusp-related phenomena are not present.