Azimuthal propagation of Pc5 geomagnetic field pulsations in the southern polar cap

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

“…The analysis of a daytime event shows that for simultaneous long-duration fluctuations, the amplitude maximizes at each station around local magnetic noon (i.e., not simultaneously), the propagation direction is antisunward, as for SW-driven waves (Kepko et al, 2002;Kim et al, 2002), and the estimated azimuthal wave number m is ∼ 4, in agreement with values found in previous studies for daytime fluctuations (Lepidi et al, 2011a) and consistently with the classification of dayside Pc5 resonances with small m as waves excited by an external mechanism (Glassmeier, 1995;Baker et al, 2003;Samson, 1991). We note that the 80 • S stations used in the present analysis are usually located at the footprint of open field lines, so they cannot directly observe FLRs; however, the FLR effects occurring at somewhat lower latitudes can be detected also at such high latitudes around local noon, when the stations approach the cusp (Lepidi et al, 1999;De Lauretis et al, 2009).…”

“…A previous analysis has shown that Pc5 pulsations at SBA and TNB (separated by 1 h in MLT) are highly coherent in the magnetic noon and midnight sectors and that they propagate preferably from midnight for the southward interplanetary magnetic field (IMF) and from noon for the northward IMF . More recently, Lepidi et al (2011a) made a comparative analysis of Pc5 pulsations at TNB and Dumont d'Urville, both located at 80 • S and separated by 5 h in MLT; they observed coherent fluctuations when the stations are on the same side with respect to the cusp; also, in this case, the propagation direction was found to be away from midnight, as expected for substorm-related phenomena, and from noon, as expected for the Kelvin-Helmholtz instability mechanism or SW pressure fluctuation transmission into the magnetosphere. Polar areas are important also to study the daily variation, which, at high latitudes, is due to two different contributions: the polar extension of the midlatitude ionospheric current systems and an additional electric current system, related to field-aligned currents, characteristic of the polar cap (Matsushita and Xu, 1982;Akasofu et al, 1983).…”

High spatial resolution radar observations of ultralow frequency waves in the southern polar cap

“…We believe that the observations presented in this paper are more consistent with the “continuous” (Pc) classification [ Jacobs et al , ], noting in particular the wave packet structure, narrow spectra, and event lifetimes of several hours (e.g., Figures and ). Therefore, the Pc5 classification may be more appropriate for the results reported in this paper and has also been used by Francia et al [], Lepidi et al [], and others. A larger statistical study would be required in order to characterize the nature of the polar cap waveforms in more detail.…”