Pc 3-4 Pulsations Near the Cusp: Observations using Search Coil Magnetometers and HF Radars on Svalbard

Details Pc 3-4 Pulsations Near the Cusp: Observations using Search Coil Magnetometers and HF Radars on Svalbard Pc 3-4 Pulsations Near the Cusp: Observations using Search Coil Magnetometers and HF Radars on Svalbard

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm23a1688e&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM23A-1688

Physics

2706 Cusp, 2731 Magnetosphere: Outer, 2752 Mhd Waves And Instabilities (2149, 6050, 7836)

Scientific paper

Pc 3-4 pulsations (f ~10-100 mHz) originating in the ion foreshock upstream of Earth's bow shock due to the interaction between reflected ions and the solar wind frequently are observed in dayside ground magnetometer records at high latitudes. Many early studies noted increased Pc 3-4 wave power in the vicinity of the dayside cusp and inferred entry via the cusp, but later studies have revealed a more complex picture. In this study, we examined power near local noon at Pc 3-4 frequencies observed by search coil magnetometers at three closely-spaced stations on Svalbard (Ny Alesund, Longyearbyen, and Hornsund). Nineteen days with clear band-limited Pc 3-4 wave power near local noon, and thirteen days with only broadband wave power, were selected for which clear cusp signatures were available in data from the Finland SuperDARN radar, which was used to accurately determine the cusp latitude. 3-s resolution fixed- beam mode data from a radar beam viewing over Svalbard also made it possible to determine Pc 3-4 periodicity in regions of the cusp and auroral zone ionosphere that returned sufficient signal. Band-limited (Pc 3-4) and broadband ULF signals in near-noon magnetometer data showed a similar latitude distribution: wave power peaked about 4-5 degrees south of the cusp. Radar backscatter from the cusp showed no evidence of Pc 3-4 modulation in this region during any of these intervals, whereas two intervals of data at lower latitudes did show modulation at Pc 3-4 frequencies. These observations are consistent not with entry via the cusp proper but along field lines equatorward of the cusp which map to the low-latitude boundary layer or outer magnetosphere. Because this location is similar to that observed for the maximum power of traveling convection vortex events / magnetic impulse events (TCVs/MIEs), we suggest that similar physics may play a role in transmitting perturbations from the upstream solar wind into the dayside magnetosphere in both cases.

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