Abstract
Abstract. We present a study of Broad-Band Extremely Low Frequency (BB-ELF) electric fields in the mid-altitude (4–6 Earth radii) cusp during periods of southward interplanetary magnetic field, using data from the Cluster spacecraft. Magnetospheric boundary layers are identified and classified according to particle precipitation characteristics. We find that the BB-ELF is contained within the cusp ion precipitation region, and its onset is closely co-located with the equatorward edge of the cusp ion dispersion signature. Previous studies have shown a positive correlation between BB-ELF and downward ion number flux. In this study, we compare the correlation coefficients of BB-ELF wave power versus the ion number and energy fluxes for upward, downward and total field-aligned fluxes. There is a greater degree of correlation between the total field-aligned flux and wave power than between the downward flux and wave power, which indicates that the BB-ELF wave generation is independent of ion beam direction. Our results support the idea of a local ion – BB-ELF wave interaction.
Highlights
A commonly occurring feature in the precipitation regions near the open-closed field line boundary (OCB) is intense low-frequency fluctuations of the electric field
There is a large spread in the data points but the average value for the Broad-Band Extremely Low Frequency (BB-ELF) latitude span shows a clear maximum around noon
We have examined the location of BB-ELF relative to the OCB and the cusp ion dispersion boundaries
Summary
A commonly occurring feature in the precipitation regions near the open-closed field line boundary (OCB) is intense low-frequency fluctuations of the electric field. Gurnett and Frank, 1977; Maynard et al, 1982; Sugiura et al, 1982; Gurnett et al, 1984; Marklund et al, 1990; Matsuoka et al, 1991, 1993; Kintner et al, 1996; Stasiewicz et al, 2000; Ivchenko and Marklund, 2001; Grison et al, 2005) This kind of fluctuations is commonly referred to as broadband extremely low frequency (BB-ELF) electric fields Ivchenko and Marklund (2001) analyzed 6 months of electric and magnetic field measurements from the Astrid-2 microsatellite, whose orbit was at an altitude of 1000 km They found that low frequency electromagnetic activity was persistently observed in the cusp region, but for periods of high geomagnetic activity in the rest of the auroral oval. They suggested that the fluctuations were caused by the energy and plasma influx from the magnetosphere
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