Dependence of Pc 3 magnetic energy spectra at south pole on upstream solar wind parameters

Abstract

In order to clarify which of two principal postulated sources of broadband 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 reexamined the statistical relationships between solar wind parameters and narrow‐band and broadband spectral powers in the Pc 3 frequency range (22–100 mHz) measured on the ground at the geographic south pole station. Both the broadband (20–45 s) and narrow‐band (20–30 s) 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 broadband powers near local noon in the cusp region and the IMF cone angle. The correlation with the solar wind speed suggests that a Kelvin‐Helmholtz type instability at the magnetopause plays an important role both in the generation of surface waves and in the amplification of already existing waves as they are convected across and transmitted through the dayside high‐latitude magnetopause.