The longitudinal polar cusp displacement from geomagnetic measurements in Antarctica

We used ULF geomagnetic field measurements in the Pc5 frequency range (1.7-7 mHz) at two Antarctic stations to statistically investigate the longitudinal location of the polar cusp. The two stations are located at the same geomagnetic latitude, similar to 80 degrees S (just poleward of the cusp), and are separated by one hour in magnetic local time. Since at each station the Pc5 power maximizes when the station approaches the cusp, the comparison between their Pc5 power allows to estimate the longitudinal position of the cusp and to examine its movements. We found that there is a displacement of the cusp depending on interplanetary conditions; in particular, the cusp shifts to later hours for negative values of the interplanetary magnetic field and solar wind velocity east-west components (B-y and V-y), while moves to earlier hours for positive values of V-y. Conversely, no dependence of the cusp longitudinal position on positive B-y values nor on the interplanetary magnetic field north-south component (B-z) emerges.