Abstract
Abstract. We examined the coast effect in Antarctica along the 80∘ S magnetic parallel. We used the geomagnetic field measurements at the two coastal stations of Mario Zucchelli Station and Scott Base, and, as a reference, at the inland temporary station Talos Dome, during 18 January–14 March 2008. Spectral analysis in the Pc5 frequency range (1–7 mHz) revealed large differences between coastal and inland stations, such as higher spectral power levels in the vertical component and higher coherence between horizontal and vertical components at coastal stations. Using the interstation method on selected active time intervals, with Talos Dome as a remote reference station, we found that remote reference induction arrows are directed almost perpendicularly with respect to their respective coastlines. Moreover, the single-station analysis shows that at Talos Dome the amplitude of the induction arrows is much smaller than at coastal stations. These results clearly indicate that coast effect at a few hundred kilometers from the coastline is relatively small. The coast effect on polarization parameters was examined, for a Pc5 event that occurred on 11 March 2008. The results evidenced that the azimuthal angle of polarized signals at one of the coastal stations is largely different with respect to the inland station (by ∼ 110∘), while the polarization ratio and ellipticity attain comparable values. We proposed a correction method of the polarization parameters, which operates directly in the frequency domain, obtaining comparable azimuthal angles at coastal and inland stations. Keywords. Ionosphere (wave propagation) – magnetospheric physics (polar cap phenomena; storms and substorms)
Highlights
Magnetospheric ultra-low-frequency waves (ULF waves, 1.7–5 Hz) driven by the solar wind are successfully studied using geomagnetic field measurements at polar latitudes (Engebretson et al, 2006; De Lauretis et al, 2010; Regi et al, 2015)
We found that the average SZ is higher at TNB and Scott Base (SBA) than at TLD and the difference increases with increasing frequency
It is worth noting that the differences between the coastal stations and the inland station tend to decrease with decreasing frequency, probably due to both the effects of a horizontally homogeneous deep lithosphere under all geomagnetic stations, which responds to the low frequencies, and the effects of uniform-inducing ULF waves at all ground stations, since at low frequencies the wavelengths are larger than the maximum distance between stations (∼ 600 km)
Summary
Magnetospheric ultra-low-frequency waves (ULF waves, 1.7–5 Hz) driven by the solar wind are successfully studied using geomagnetic field measurements at polar latitudes (Engebretson et al, 2006; De Lauretis et al, 2010; Regi et al, 2015). Regi et al.: Coast effect in Antarctica observatories on the coastline, since the higher seawater conductivity provides a larger vertical field with respect to the land In this case, the variation field still lies in a plane, the “Parkinson plane”, which is no longer horizontal but is tilted upward toward the sea (Parkinson and Jones, 1979). As pointed out by Schmucker (1970) and Viljanen et al (1995) (see Fujiwara and Tou, 1996; Beamish, 1982; Vujicand Brkic, 2016), a suitable analysis in both vertical and horizontal components can be assessed by using a reference station, which should be ideally far away from the ground anomalies (i.e., from the coast) In this regard, we used as a reference station the temporary installation at Talos Dome (TLD, ∼ 80◦ S), deployed during the 2007– 2008 Antarctic campaign at ∼ 270 and 560 km from TNB and SBA, respectively, and operating during 18 January– 14 March 2008 (Lepidi et al, 2017). By examining a Pc5 case event, we observed different polarization characteristics in the horizontal geomagnetic field variations at TNB and TLD, which can be due to the closeness of TNB to the coastline, as suggested by De Lauretis et al (2005)
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