Conjugate ULF field line resonances at cusp lattiudes

Significant similarities have been identified in the dynamic power spectra of induction magnetometer data recorded at the conjugate cusp stations of Davis, Antarctica (mlat -74.3, mlong 101.5) and Longyearbyen, Svalbard (mlat 75.0, mlong 114.5). A 60 day period in 1993 (January-February) has been studied to characterise two common features, 1) Broadband Pc5 bursts which predominantly occur 2-4 hours before and after local magnetic noon, and which exhibit polarisations suggestive of a Kelvin-Helmholtz-like source mechanism, and 2) A resonance structure which has’ an arch-shaped local time dependence. Interhemisphere phase measurements indicate oddmode toroidal standing-waves after field line resonance and azimuthal propagation effects are taken into account. Phase studies such as this may be used to study conjugacy at high latitudes and identify the location of the open and closed field line boundary, an important diagnostic parameter in space weather studies