Dependence of Pc 3 magnetic energy spectra at South Pole on upstream solar wind parameters.

In order to clarify which of two principle postulated sources of Pc 3 magnetic pulsations, i.e., upstream waves in the earth's foreshock and surface waves on the dayside magnetospheric boundary, dominates at high latitudes near the cusp, we re-examined the statistical relationships between solar wind parameters and narrow and broad-band spectral powers in the Pc 3 frequency range (22 to 100 mHz) measured on the ground at South Pole Station. Both the broad (20-45 s) and narrow (20-30 s) band magnetic powers measured at South Pole Station show good correlations with the hourly-averaged solar wind speed, but little (or no) correlations with the hourly-averaged interplanetary magnetic field (IMF) cone angle or with the theoretically-inferred reflected ion-beam speed in the earth's foreshock. We also find no relationship between Pc 3 pulsation activity in the cusp region and the IMF cone angle.