Polarization characteristics of Pc5 magnetic pulsations in the dusk hemisphere

Abstract Pc5 magnetic pulsations are known to have maximum amplitude in the latitudinal regime occupied by the auroral oval. It has long been surmized that such pulsations originate through the action of the Kelvin-Helmholtz instability on the magnetopause boundary. This study presents a comprehensive analysis of the polarization characteristics of Pc5 pulsations using data from a meridian line of magnetometers straddling the auroral oval in the afternoon and dusk sectors. We find the latitudinal variation of the polarization characteristics to be inconsistent with a simple Kelvin-Helmholtz instability hypothesis particularly in the local time interval between noon and dusk. We also find afternoon sector Pc5 pulsations to be a rather rare phenomenon compared to their morning sector counterparts. The afternoon sector events seem to have a tendency to occur during episodes of northward interplanetary magnetic field and, in general, appear to be triggered by impulses which have global signatures at times of quiescence or decreasing magnetospheric activity. We suggest that, in contrast to morning sector Pc5 activity which appears to originate through the action of a Kelvin—Helmholtz instability at the interface between the low latitude boundary layer and central plasma sheet, afternoon sector Pc5 events originate as compressional effects with some of the associated energy being coupled into the shear Alfven mode.

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