High-latitude observations of impulse-driven ULF pulsations in the ionosphere and on the ground

Abstract

Abstract.We report the simultaneous observation of 1.6-1.7 mHz pulsations in the ionospheric F-region with the CUTLASS bistatic HF radar and an HF Doppler sounder, on the ground with the IMAGE and SAMNET magnetometer arrays, and in the upstream solar wind. CUTLASS was at the time being operated in a special mode optimized for high resolution studies of ULF waves. A novel use is made of the ground returns to detect the ionospheric signature of ULF waves. The pulsations were initiated by a strong, sharp decrease in solar wind dynamic pressure near 09:28 UT on 23 February 1996, and persisted for some hours. They were observed with the magnetometers over 20 • in latitude, coupling to a field line resonance near 72 • magnetic latitude. The magnetic pulsations had azimuthal m numbers ∼−2, consistent with propagation away from the noon sector. The radars show transient high velocity flows in the cusp and auroral zones, poleward of the field line resonance, and small amplitude 1.6-1.7 mHz F-region oscillations across widely spaced regions at lower latitudes. The latter were detected in the radar ground scatter returns and also with the vertical incidence Doppler sounder. Their amplitude is of the order of ±10 m s −1 . A similar perturbation frequency was present in the solar wind pressure recorded by the WIND spacecraft. The initial solar wind pressure decrease was also associated with a decrease in cosmic noise absorption on an imaging riometer near 66 • magnetic latitude. The observations suggest that perturbations in the solar wind pressure or IMF result in fast compressional mode waves that propagate through the magnetosphere and drive forced and resonant oscillations of geomagnetic field lines. The compressional wave field may also stimulate ionospheric perturbations. The observations demonstrate that HF radar ground scatter may contain important information on small-amplitude features, extending the scope and capability of these radars to track features in the ionosphere.

Pc3-4 ULF waves observed by the SuperDARN TIGER radar

“…As we mentioned in the Introduction, their generation is commonly attributed to the ion-cyclotron instability in the proton beams reflected from the Earth's bow shock (e.g. Fairfield, 1969;Paschmann et al, 1979). Ponomarenko et al (2002) showed that, through its dependence on solar wind parameters, the signal component most likely originates from the upstream ion-cyclotron instability in reflected proton beams (e.g.…”

“…Due to their well-established dependence on solar wind and IMF parameters, it is widely believed that at least some of the daytime band-limited Pc3-4 MHD waves may be generated upstream of the Earth's bow shock by the ion-cyclotron instability in reflected proton beams (Fairfield, 1969;Paschmann et al, 1979;Hoppe and Russell, 1983).…”

“…Rishbeth and Garriott, 1964), including oblique sounding using sea/ground scatter (e.g. Bourdillon et al, 1989;Menk et al, 2003) or scattered by ionospheric irregularities (e.g. Walker et al, 1979).…”

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

“…Here, however, the waves are typically visible as modulations of ground backscatter, as first exploited by Menk et al (2003). developed a new visualistion technique which greatly enhances the ability to identify such modulated ground backscatter returns, and the use of this technique is illustrated in Fig.…”

Evidence of transverse magnetospheric field line oscillations as observed from Cluster and ground magnetometers

“…The cavity formed by magnetospheric boundaries can be set into oscillation by impulsive driving such as solar wind pressure variation (Menk et al, 2003) or broad band driver such as Kelvin-Helmholtz waves (Chen and Hasegawa, 1974b;Mann et al, 1999). Such oscillations of the magnetospheric waveguide might then cause a local field line to oscillate at its natural frequency where this frequency matches one of the waveguide harmonics Samson et al, 1992;Walker et al, 1992;Wright, 1994;Rickard and Wright, 1994).…”