The geomagnetic coast effect at two 80° S stations in Antarctica, observed in the ULF range

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 singlestation 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.

Geomagnetic Activity at Lampedusa Island: Characterization and Comparison with the Other Italian Observatories, Also in Response to Space Weather Events

“…Results show that the most remarkable variations emerge in the H component; in particular, for the minima of SymH, LMP has the greatest significant deviation due to its lower latitude [45]. Moreover, the vertical component at LMP exhibits a low enhancement in correspondence and just after the events, suggesting a link with an inductive effect due to electric currents system developing in the ground and in the surrounding conductive sea salt water [37,74,75]. At Italian latitudes, in correspondence to stronger events, such inductive effects could generate the so-called ground induced currents (GICs) (see [76,77]), which typically occur and attain higher intensity at higher latitudes.…”

“…In our case, we used the moving average, which represents a simple and efficient method for identifying long trends (e.g., [22,23,34,35]). In this regard, since diurnal variations have a periodicity of 24 h (and its sub-harmonics, 12, 8, 6, 4 h, and so on), we computed the moving average over 3 days: this value is sufficient to efficiently suppress the daily variations and not too large to include sub-harmonics of 27-day Sun's synodic rotation period (see in particular [36,37]). We then subtracted the 3-day moving averaged time series from the original ones.…”

ULF Geomagnetic Activity Signatures in the Atmospheric Parameters in Antarctica

“…2.1 ULF interaction with relativistic electrons in the outer radiation belts ULF magnetohydrodynamic waves received particular attention in the past decades [18][19][20][21][22][23], since they provide a convenient probe of the magnetosphere, by means of ground [24][25][26] and/or satellites magnetic field measurements [22,[27][28][29][30] as well as inspect ground conductivity [31][32][33].…”

On the validation of K index values at Italian geomagnetic observatories

“…We want to point out that it does not exist an unique K9 at a given geomagnetic latitude since the geomagnetic activity shows a well known magnetic local time (MLT) dependency and, in addition, each site could be affected by different local features such as, for example, crustal anomalies (Chiappini et al, 2000) and/or coast effect (Parkinson, 1962;Regi et al, 2018). For the inclusion of a new geomagnetic observatory into the INTERMAGNET network, K9 should be assigned, for example, by comparing geomagnetic field variations between the new observatory and the historical ones for which K indices are estimated by using well defined K9 levels, obtained from a long time observation.…”