| Summary: | Magnetometer data from Davis, Antarctica (74.50 S, 99.80 E CGM-1996) are particularly favourable for examining the spectral characteristics due to geomagnetic field lines resonances near the open-closed field line boundary of the magnetosphere. Field line resonance (FLR) signatures of closed field lines at high latitudes on the dayside magnetosphere show diurnal variations in frequency where maximum power occurs in the Pc5 (1-10 mHz) band. Previous research has suggested that the length of closed field lines threading the ground stations is a major factor that deterntines the FLR frequencies. The general topology of the dayside magnetopause results in longer field lines and therefore lower resonant frequencies on the dawn and dusk flanks and the shortest field lines with corresponding higher resonant frequencies near noon. These features yield an arch-shaped variation in frequency with local magnetic time. We compare eigen-function solutions of ULF wave modes that include the curvature and torsion in the geomagnetic field with data from the Davis magnetometer. Including the curvature and torsion effects provides an explanation for our observation of a dip (or saddle) in the Pc5 arch, observed as a decrease in frequency centred on local magnetic noon, that is often seen in high latitude magnetometer data.
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