CLUSTER observations of lower hybrid waves excited at high altitudes by electromagnetic whistler mode signals from the HAARP facility

Abstract

We report new observations from the CLUSTER spacecraft of strong excitation of lower hybrid (LH) waves by electromagnetic (EM) whistler mode waves at altitudes ≥20,000 km outside the plasmasphere. Previous observations of this phenomenon occurred at altitudes ≤7000 km. The excitation mechanism appears to be linear mode coupling in the presence of small scale plasma density irregularities. These observations provide strong evidence that EM whistler mode waves are continuously transformed into LH waves as the whistler mode waves propagate at high altitudes beyond L ∼ 4. This may explain the lack of lightning generated whistlers observed in this same region of space.

Cluster observations of ELF/VLF signals generated by modulated heating of the lower ionosphere with the HAARP HF transmitter

“…Closer examination of the detected pulses shows that at both frequencies there actually are two pulses roughly centered close to the nominal frequency, separated in frequency by approximately 25 Hz. These sideband waves have been interpreted as being lower hybrid (LH) waves possibly generated through linear mode coupling in the presence of small-scale plasma density irregularities (Bell and Ngo, 1990;Bell et al, 2004).…”

Observations of Turbulence Generated by Magnetic Reconnection

“…Here, although it is possible that whistler waves may be scattering off plasma density variations and converting into lower hybrid fluctuations [21][22][23], the anomalous resistivity associated with the lower hybrid waves is still found to be small; η ∼ 10 −3 Ωm [24]. Given a cross tail current density of ∼ 10 −8 Am −2 , this corresponds to an electric field of ∼ 0.01mV m −1 , (< 1% of the reconnection electric field) meaning that any modification to the overall reconnection rate is negligible.…”

Whistlers observed outside the plasmasphere: Correlation to plasmaspheric/plasmapause features

“…Supported by simultaneous Waves of High frequency and Sounder for Probing of Electron density by Relaxation (WHISPER) observations of electron density, the Platino et al [2005] study presents evidence that whistlers are observed in the low-density regions outside the plasmasphere only in the presence of large-scale irregularities within which the wave can be ducted. Furthermore, Platino et al [2005] argue that the Cluster observations of lightning-generated whistlers outside the plasmasphere support the theory of the loss of the electrostatic whistler mode energy via mode conversion to quasi-static lower hybrid waves [Bell and Ngo, 1990;Bell et al, 2004]. This work will place the Cluster-observed whistlers presented by Platino et al [2005] into a global context with respect to the plasmasphere/plasmapause itself by employing the near-real-time monitoring of the global structure and dynamics of Earth's plasmasphere provided by the Extreme Ultraviolet Imager (EUV) imager aboard the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite.…”

“…We then conclude this report with a discussion in section 4 of the implications that these associated Cluster/EUV observations have for the whistler wave propagation beyond the plasmasphere, whistler mode conversion theory as proposed by Bell et al [2004] and the potential consequences for radiation belt populations exposed to these escaping lightning-generated whistler waves. More to the point, we argue that the density irregularities necessary for the ducting of lighting-generated whistlers to locations outside of the plasmasphere are a direct consequence of the localized-and perhaps filamentary-inner magnetospheric electric fields responsible for the formation of these larger-scale plasmaspheric features and lower latitude access to ducting channels afforded sferics by the formation of these features.…”

“…Additionally, these authors make the case that their observations, supported by ray tracing simulations, agree with the hypothesis that the lack of lightning-generated whistler observations beyond the plasmapause is a consequence of the mode conversion of electromagnetic whistler mode waves to quasi-electrostatic lower hybrid waves. These mode-converted lower hybrid waves then propagate from the region of their excitation, dissipating the electromagnetic whistler wave energy [Bell and Ngo, 1990;Bell et al, 2004]. In addition, the ray tracing simulations of Platino et al [2005] suggest that the mode conversion between whistler and lower hybrid modes can occur several times during the course of the whistler wave propagation, leading to highly dispersed whistlers with observational lifetimes of a second or more.…”