Pc 3-4 Pulsations Near the Cusp: Latitude dependence near the open-closed field line boundary

Details Pc 3-4 Pulsations Near the Cusp: Latitude dependence near the open-closed field line boundary Pc 3-4 Pulsations Near the Cusp: Latitude dependence near the open-closed field line boundary

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm23a1689y&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM23A-1689

Physics

2706 Cusp, 2752 Mhd Waves And Instabilities (2149, 6050, 7836), 2784 Solar Wind/Magnetosphere Interactions

Scientific paper

Dayside ground magnetometer records at high latitudes frequently show evidence of Pc 3-4 pulsations (f ~ 10-100 mHz) which originate in the ion foreshock upstream of the Earth's bow shock due to the interaction between reflected ions and the solar wind. Previous studies have noted increased Pc 3-4 wave power in the vicinity of the dayside cusp and inferred that the upstream waves gained entry via the cusp, although more recent studies have revealed a more complex picture. Here, we examine Pc3-4 wave power near local noon observed by search coil magnetometers at three closely-spaced stations on Svalbard. Three intervals are chosen when the upstream conditions are favourable for Pc3-4 generation, clear band-limited Pc3-4 wave power is observed near local noon, and an extended interval of HF radar backscatter indicative of the cusp is detected by the Hankasalmi SuperDARN radar. A stereo mode of radar operation is employed, such that 3 s time resolution is available on one radar beam, whilst the high latitude convection is revealed with 1 min. resolution. The location of the equatorward edge of the HF radar cusp may then be directly compared with the Pc3-4 wave power measured at three latitudes as the cusp migrates across the stations. The radar data show clear evidence of transient ionospheric flows and high spectral widths associated with field lines newly- opened by dayside reconnection processes, but no evidence of oscillations in the Pc3-4 frequency range. In the ground magnetic field a peak in Pc3-4 power is generally observed in the equatormost magnetometer, except when the cusp is significantly poleward of the stations, consistent with a peak in wave power ~4 degrees equatorward of the cusp, but suggesting a modest dependence of wave power with latitude on closed field lines When the cusp does move equatorward of the magnetometer stations the Pc3-4 power drops rapidly, and does so earliest at the most poleward magnetometer station, suggesting a sharp drop in wave power when the open field line region is reached. This behaviour is confirmed by comparison of Pc3-4 wave power recorded at Svalbard with that recorded at lower latitudes at Halley Bay in Antarctica. These observations are not consistent with entry via the cusp proper, but rather along closed field lines equatorward of the cusp which map to the low-latitude boundary layer or outer magnetosphere.

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