Asymmetry in Stimulated Emission Polarization and Irregularity Evolution During Ionospheric Electron Gyroharmonic Heating

Abstract

The first report is made of a holistic investigation of stimulated electromagnetic emission (SEE) during ionospheric electron gyroharmonic heating using a diagnostic approach at the High Frequency Active Auroral Research Program facility. The evolution of SEE polarization and plasma irregularity development near the third electron gyroharmonic 3f ce is investigated, which provides new insights into SEE generation mechanisms by the associated parametric decay instabilities. New more complex SEE spectral line behavior is clearly observed for varying transmitter beam angles. New SEE spectral emissions are observed at ∼75 kHz when pumping below 3f ce . The high-frequency radar echoes and SEE polarimetry appear asymmetric for pumping above 3f ce , which implies that the broad upshifted maximum spectral line formation involves plasma irregularities scattered by high-frequency radar echoes. This has important implications for understanding artificial ionization layer generation during ionospheric modification.Plain Language Summary Nonlinear interaction of high-power electromagnetic waves and magnetized plasmas produces a plethora of fundamental phenomena that can be exploited for powerful diagnostics of the Earth's ionospheric plasma. Stimulated electromagnetic emissions (SEEs) and plasma density turbulence, observable with high-frequency radars, arise from this nonlinear interaction as well as artificial ionization layers. The later has received considerable attention recently due to the importance of the associated fundamental physics and chemistry processes as well as the implications for modern communication and navigation systems. Artificial ionization layers are still not well understood, and this work seeks to provide insight into the generation mechanism by reporting the first results of a novel diagnostic approach that utilizes SEE and high-frequency radar measurements. The experiments were performed at the High Frequency Active Auroral Research Program facility. The evolution of SEE polarimetry and turbulent plasma density structures exhibits a prominent asymmetry when sweeping the transmitter frequency near electron gyrohamonic frequencies. A direct connection was observed between the plasma density structures and SEE spectral lines known to be associated with ionization layers. The observed asymmetric behavior therefore provides new insights into the linkage between ionization layers and generation of plasma density structures with specific characteristics. , S. J. (2018). Asymmetry in stimulated emission polarization and irregularity evolution during ionospheric electron gyroharmonic heating. Geophysical Research Letters, 45,[9363][9364][9365][9366][9367][9368][9369][9370][9371]

Properties of the Stimulated Electromagnetic Emissions During the Inclined High‐Frequency Pumping of the Ionosphere Near the Fourth Electron Gyroharmonic at the High‐Frequency Active Auroral Research Program Facility

“…Previously, SEE properties were studied with fast pump frequency sweeps mainly for vertical pumping (Carrozzi et al, ; Kotov et al, ), including several experiments for s = 4 with the pump beam inclined to the MZ performed at HAARP for α = 14° (Bernhardt et al, ; Grach et al, ; Sergeev et al, , ) and at “Sura” for α = 14° and 18° (Kotov et al, ). Some results were obtained also in similar experiments for s = 3 and 14° < α < 28° at HAARP (Fu et al, ).…”

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

“…between SEE with electron temperature, plasma irregularities, HF-induced plasma, and ion lines has also been investigated at EISCAT (Honary et al, 1995) and HAARP (Fu et al, 2018;Mahmoudian et al, 2016).…”

“…At Arecibo, SBS emissions including IA and EIC have also been observed by Djuth et al (2018) and Mahmoudian, Nossa, et al (2019). Meanwhile, the correlation between SEE with electron temperature, plasma irregularities, HF‐induced plasma, and ion lines has also been investigated at EISCAT (Honary et al, 1995) and HAARP (Fu et al, 2018; Mahmoudian et al, 2016).…”

Recent ionospheric investigations in China (2018–2019)

“…Fu HY et al (2018a) investigated the asymmetry in stimulated emission polarization and irregularity evolution during ionospheric electron gyroharmonic heating. High‐frequency radar echoes and stimulated electromagnetic emission (SEE) polarimetry appear asymmetric for pumping above 3 f ce ( f ce , the electron cyclotron frequency), implying that the broad upshifted maximum spectral line formation involves plasma irregularities scattered by high‐frequency radar echoes.…”