A statistical analysis of low‐frequency magnetic pulsations at cusp and cap latitudes in Antarctica

Abstract

We report a statistical analysis of low‐frequency magnetic variations (magnetic pulsations, 0.8–7 mHz) at South Pole (74°S corrected geomagnetic latitude) and Terra Nova Bay (80°S) during 1996. The results show that at South Pole (at cusp latitudes) the pulsation power exhibits two maxima during the day, one in the local premidnight and the other in the morning. The first maximum disappears when the analysis is restricted to northward interplanetary magnetic field conditions (Bz > 1 nT), suggesting that it might be associated to substorm phenomena. During closed magnetospheric conditions, when the cusp is expected to be located poleward with respect to the station, the spectral and polarization characteristics of pulsations between 1 and 3 mHz suggest that resonant oscillations of the outermost closed field lines commonly occur at South Pole in the local morning. At Terra Nova Bay, in the polar cap, the pulsation power is much lower and its diurnal variation is characterized by a single maximum, which occurs around local noon, when the station approaches the cusp. The corresponding polarization pattern indicates that Terra Nova Bay is always located poleward with respect to resonant field lines.

ULF geomagnetic pulsations at different latitudes in Antarctica

“…Several studies based on our ULF facility in Antarctica at TNB (operating since 1994) showed a significant ULF wave activity in the polar cap, both in the low and mid-frequency range (Villante et al, 2000a, b;Francia et al, 2005). Namely, the Pc3-5 power exhibits a magnetic local time (MLT) dependence, characterized by a broad maximum around noon, when the station approaches the dayside cusp and closed field lines, and a strongly reduced nighttime activity.…”

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

“…The event occurring before midnight is characterized by a definitely lower fluctuation amplitude with respect to the one around noon; in this sense we remind that around 80 • S latitude the fluctuation power level maximizes around local geomagnetic noon, when the station approaches the polar cusp (Ballatore et al, 1998;Santarelli et al, 2003). Our results show that, although at 80 • S there is not the power peak around midnight which is observed at cusp latitudes (Francia et al, 2005), the propagation direction of low frequency pulsations indicates the presence, around midnight, of substorm-related phenomena (Kangas et al, 1976;Olson, 1986); these nightime pulsations consist of short duration wave packets, while long duration trains can be sometimes detected in the daytime sector.…”

“…Moreover, these local field lines can directly connect to the interplanetary magnetic field (IMF), giving rise to a direct access of solar wind particles in the magnetosphere and to phenomena related to magnetic energy release and particle acceleration (Gonzalez et al, 1999;Lui, 2001;Phan et al, 2005).…”

A study of geomagnetic field variations along the 80° S geomagnetic parallel

“…The Pc5 fluctuation power at all stations presents the wellknown maximum around local magnetic noon, when the stations approach the polar cusp and the local field lines are closer to the magnetopause (Lepidi et al, 1996;Villante et al, 2000;Francia et al, 2005), and a minimum in the magnetic postmidnight sector. It is worth noting that the daytime Pc5 power maximum at high-latitude stations could be considered as a marker of the auroral oval position .…”

“…In previous studies we used measurements from the Italian Geomagnetic Observatory Mario Zucchelli Station (TNB, formerly Terra Nova Bay), at 80 • S corrected geomagnetic latitude, and from the French-Italian Observatory Concordia at Dome C (DMC) close to the geomagnetic pole, in order to characterize the ultra low-frequency (ULF; 1 mHz-1 Hz) pulsation activity and its relation with SW parameters in the Antarctic region (Lepidi et al, 1996Villante et al, 2000;Francia et al, 2005Francia et al, , 2009.…”