Searching for ULF signatures of the Cusp: Observations from search coil magnetometers and auroral imagers in Svalbard

Details Searching for ULF signatures of the Cusp: Observations from search coil magnetometers and auroral imagers in Svalbard Searching for ULF signatures of the Cusp: Observations from search coil magnetometers and auroral imagers in Svalbard

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsm42a..02e&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #SM42A-02

Physics

2706 Cusp, 2716 Energetic Particles: Precipitating, 2736 Magnetosphere/Ionosphere Interactions (2431), 2752 Mhd Waves And Instabilities (2149, 6050, 7836)

Scientific paper

Spacecraft traveling through the cusp at altitudes ranging from near the magnetopause to just above the ionosphere have consistently found the cusp to be filled with intense but irregular power in both electric and magnetic fields in the upper ULF frequency range (up to at least 4 Hz). Ground-based induction magnetometers have for many years observed Pc 1-2 (electromagnetic ion cyclotron) waves in this same frequency range at various latitudes including near the footpoint of the cusp, but it has not been possible with magnetometers alone to either confirm or deny a cusp source for any of these waves, partly because of the occurrence of horizontal ducting of these waves in the ionosphere. We report here on the first simultaneous, collocated observations of a set of induction magnetometers installed at three sites on Svalbard (Longyearbyen, Ny Alesund, and Hornsund), and auroral imagers also located at the first two of these sites. Data during northern winter 2006-2007, when the cusp footpoint was in darkness, showed occasional narrowband Pc 1-2 wave events, frequent broadband noise when energetic particle precipitation occurred overhead, but the consistent absence of broadband ULF power above the noise level when only soft cusp precipitation was overhead. The intensity of narrowband Pc 1-2 wave events most often increased toward lower latitudes, consistent with wave sources on closed field lines. However, on one day when the cusp was observed to be equatorward of Longyearbyen, band-limited Pc 1-2 wave power was strongest at Ny Alesund, the northernmost station. This latter observation is consistent with waves originating in the plasma mantle just poleward of the cusp, as was found in a recent study using the Polar satellite and more widely spaced ground-based ULF observations by Engebretson et al. [2005], and again suggests that the cusp proper is not the source of any narrowband Pc 1-2 wave activity that can be observed on the ground, and little if any broadband activity as well.

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