Electron Temperature Inversion by Stimulated Brillouin Scattering During Electron Gyroharmonic Heating at EISCAT

Abstract

This work reports a holistic experimental investigation of stimulated Brillouin scattering (SBS) features and electron temperature inversion near the third electron gyroharmonic 3fce using the European Incoherent Scatter (EISCAT) heating facility. The evolution of SBS features including spectral offset, width, and power varies asymmetrically near 3fce. The asymmetries among SBS, electron temperature, and high frequency‐enhanced ion lines are clearly exhibited for pumping above f0 ≥ 3fce. Electron temperature Te at the resonance regime has been retrieved from the measured SBS spectra based on the wave matching theory. The inversion results by SBS are consistent with measurement by the EISCAT UHF incoherent scatter radar (ISR) at the resonance altitude. The comparison of electron temperature Te and ion temperature Ti between SBS and ISR enlightens great potentials for developing realistic ionospheric diagnostic technique.

Ion Gyro‐Harmonic Structures in Stimulated Emission Excited by X‐Mode High Power HF Radio Waves at EISCAT

“…Excited electrostatic waves in the ionosphere source region could be either ion-acoustic (IA) or electrostatic ion cyclotron (EIC) waves, depending on the angle between the wave vector and the background magnetic field vector B. IA waves were excited in the interaction region along the magnetic field B and the EIC waves were dominant nearly perpendicular to B, that is consistent with the theoretical predictions (Bernhardt et al, 2010;Shukla & Stenflo, 2010). European incoherent Scatter (EISCAT) O-mode HF pumping experiments with frequency stepping through the third 3f ce and fourth 4f ce electron gyro-harmonics (Borisova et al, 2014;H. Y. Fu et al, 2020) have demonstrated that MSBS IA lines were excited above and below electron gyro-harmonics and suppressed as the pump frequency approached close to 3f ce and 4f ce .…”

Controlled beat-wave Brillouin scattering in the ionosphere

“…5). In previous Brillouin experiments [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] , only the pump wave 0 was transmitted while wave 1 occurred naturally as SEE escaping the ionosphere and was recorded on the ground as a downshifted sideband. The physical process of natural SBS involves a nonlinear interaction in which the incident (pump) EM wave 0 decays into an electrostatic IA wave 2 and a scattered EM wave 1 that grow via the SBS instability 14,40 , where the electrostatic IA wave 2 is initially excited by noise-like fluctuations in the plasma.…”

“…The first observations of stimulated Brillouin scattering in ionospheric experiments were reported from the Jicamarca radar and at Arecibo 31,32 when the transmitted frequency f 0 was significantly higher than the maximum plasma frequency of the ionosphere, making the ionosphere transparent to the EM wave. More recently, there were also clear observations of SBS during ionospheric heating experiments for f 0 below the maximum plasma frequency so that the ionosphere was opaque to the EM wave [33][34][35][36] . In addition, experiments have demonstrated scattering of the EM wave off ion cyclotron/Bernstein waves [37][38][39][40][41][42][43][44][45][46][47] .…”

“…1), on 29 November 2014, and analyse the results by means of numerical simulations. To avoid saturation by the direct signal from the transmitter (if the reception of the probe was to be carried out at Ramfjordmoen using the HF receiver), the remote SEE receiver 36,39 installed at Kroken was instead used to record the signal. As seen in Fig.…”

Multi-frequency SuperDARN radar observations of the modulated ionosphere by high-power radio-waves at EISCAT

“…The excited SEEs (Stimulated Electromagnetic Emissions) within 1 kHz to 100 kHz (known as wideband SEE or WSEE) of the HF pump radio-waves have been investigated in detail over the past three decades (Leyser, 2001). The recent studies have also revealed new unique features within 1 kHz of the HF pump field, which is known as narrowband SEE (NSEE) features (Norin et al, 2008;Bernhardt et al, 2009Bernhardt et al, , 2010Bernhardt et al, , 2011Bordikar et al, 2013Bordikar et al, , 2014Fu et al, 2013Fu et al, , 2015Mahmoudian et al, 2013aMahmoudian et al, , b, 2014aMahmoudian et al, , b, 2016Mahmoudian et al, , 2019aYellu et al, 2018aYellu et al, , b, 2019. The recent works have proved the capability of SEE measurements in studying the excited plasma waves as well as the plasma related phenomena such as wave-particle interaction and non linear saturation, in the heated ionosphere.…”