HF radar observations of Pc5 ULF pulsations driven by the solar wind

Abstract

[1] We present HF radar observations of Pc5 field line resonances in the post-midnight Antarctic ionosphere on April 28/29 1997. Simultaneous oscillations were seen in the solar wind parameters observed by WIND. The spectra of both sets of data show peaks near 1.3 mHz, 1.9 mHz, 2.7 mHz and 3.3 mHz. The data were bandpass filtered and a complex demodulation technique applied to calculate the instantaneous energy flux in the solar wind in each band and hence the power incident on the front of the magnetosphere 70 minutes later. The magnitude of the instantaneous power deposited in the ionosphere at each frequency through Joule heating followed this closely and was an order of magnitude smaller. We conclude that, at least on this occasion, the field line resonances could have been directly driven by the solar wind oscillations.

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…Prikryl et al (1998Prikryl et al ( , 2002 also suggested a direct link between Alfvénic solar wind fluctuations and Pc5 field line resonance observations observed equatorward of the cusp on closed field lines. Stephenson and Walker (2002) similarly presented an analysis of upstream solar wind data and SuperDARN velocity data demonstrating that, at least on occasion, common spectral peaks are observed in both, suggesting direct driving of magnetospheric field line oscillations by wave activity in the solar wind.…”

Phase coherence analysis of a field line resonance and solar wind oscillation

“…[3] Recent work has proposed that discrete compressional MHD oscillations [Stephenson and Walker, 2002;Eriksson et al, 2006] and Alfvenic oscillations [Prikryl et al, 1998] in the solar wind may directly drive magnetospheric FLRs. Other studies have shown similarities between individual discrete solar wind compressional oscillations and global magnetospheric pulsations observed in geosynchronous magnetic fields [Kepko and Spence, 2003] and in low latitude ground based magnetometer measurements [Villante et al, 2007].…”

Large-scale coordinated observations of Pc5 pulsation events

“…Other ways of exciting the cavity include the mechanism of Mann et al (1999), who showed how the overreflection mechanism could extract energy from the shear motion at the boundary. Observations of some events show correlation with coherent waves in the solar wind (Kepko et al, 2002;Stephenson and Walker, 2002). These can excite the cavity modes (Walker, 2002) and hence excite the field line resonance.…”

“…When observed in the meridian plane the oscillation appears to be standing. There is generally phase advance in the azimuthal direction, which is characterized by the azimuthal wave number m. Various sources have been identified such as Kelvin-Helmholtz oscillations at the magnetopause (Southwood, 1968), excitation of cavity or waveguide modes (Kivelson and Southwood, 1985;Samson et al, 1992), direct control by oscillations in the solar wind (Stephenson and Walker, 2002), and more recently fluctuating field-aligned currents in the auroral zone (Pilipenko et al, 2016). Pulsations can also be generated by drift-bounce resonance with ring current particles (Dungey, 1965).…”