Propagation of low frequency geomagnetic field fluctuations in Antarctica: comparison between two polar cap stations

Abstract

Abstract. We conduct a statistical analysis of the coherence and phase difference of low frequency geomagnetic fluctuations between two Antarctic stations, Mario Zucchelli Station (geographic coordinates: 74.7 • S, 164.1 • E; corrected geomagnetic coordinates: 80.0 • S, 307.7 • E) and Scott Base (geographic coordinates: 77.8 • S 166.8 • E; corrected geomagnetic coordinates: 80.0 • S 326.5 • E), both located in the polar cap. Due to the relative position of the stations, whose displacement is essentially along a geomagnetic parallel, the phase difference analysis allows to determine the direction of azimuthal propagation of geomagnetic fluctuations. The results show that coherent fluctuations are essentially detectable around local geomagnetic midnight and, in a minor extent, around noon; moreover, the phase difference reverses in the night time hours, indicating a propagation direction away from midnight, and also around local geomagnetic noon, indicating a propagation direction away from the subsolar point. The nigh time phase reversal is more clear for southward interplanetary magnetic field conditions, suggesting a relation with substorm activity.The introduction, in this analysis, of the Interplanetary Magnetic Field conditions, gave interesting results, indicating a relation with substorm activity during nighttime hours.We also conducted a study of three individual pulsation events in order to find a correspondence with the statistical behaviour. In particular, a peculiar event, characterized by quiet magnetospheric and northward interplanetary magnetic field conditions, shows a clear example of waves propagating away from the local geomagnetic noon; two more events, occurring during southward interplanetary magnetic field conditions, in one case even during a moderate storm, show waves propagating away from the local geomagnetic midnight.

Twenty years of geomagnetic field observations at Mario Zucchelli Station (Antarctica)

“…This feature clearly emerges also from fig. 7 (adapted from Santarelli et al, 2007b), where we show a pulsation event recorded at TNB (red line) and at another Antarctic station, Scott Base (SBA, blue line), which has a longitudinal displacement of about 1 hour in magnetic local time with respect to TNB (table I). At both stations there is a sustained wave activity (upper panel); from the 1-5 mHz filtered data (lower panel) it is evident that the wave activity at the two stations is very similar, but the amplitude is larger at SBA around 17-18 UT and at TNB around 21-22 UT, i.e.…”