A Stimulated Emission Diagnostic Technique for Electron Temperature of the High Power Radio Wave Modified Ionosphere

• Published in: Geophysical research letters Vol. 49; no. 15
• Main Authors: Fu, H. Y., Jiang, M. L., Vierinen, J., Häggström, I., Rietveld, M. T., Varberg, E., Sato, H., Wu, J., Scales, W. A., Jin, Y. Q.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.08.2022; Wiley
• Subjects: Artificial neural networks; Correlation; Diagnostic techniques; Electromagnetic radiation; Electron energy; electron temperature inversion; Emissions; High frequency; Incoherent scatter radar; Inversion; Ion temperature; Ionosphere; ionospheric modification; Line spectra; Methods; Neural networks; Nonlinear waves; Parameter modification; Particle interactions; Physics; Plasma turbulence; Plasmas (physics); Radar; Radio waves; Scattering; stimulated Brillouin scattering; Stimulated emission; Temperature inversion; Temperature inversions; Temperature ratio; Theories; Turbulence; Width
• ISSN: 0094-8276; 1944-8007; 1944-8007
• DOI: 10.1029/2022GL099390

We report observations of stimulated electromagnetic emission (SEE) induced by high power high frequency (HF) radio waves near the third electron gyroharmonic (3fce ${f}_{\mathrm{ce}}$) at European Incoherent Scatter Radar (EISCAT). It is discovered that stimulated Brillouin scattering (SBS) spectrum behaves similarly as spectral ion lines of the incoherent scatter radar (ISR) for HF pumping frequency above 3fce ${f}_{\mathrm{ce}}$. The SBS spectral width shows correlation with electron to ion temperature ratio Te/Ti. A new inversion method is proposed by incorporating the SBS spectral width within an artificial neural network approach to achieve electron temperature inversion for ionospheric turbulent plasmas. This work provides a potential new technique to diagnose parameters in the modified ionosphere when the ISR is not available. Plain Language Summary Nonlinear interaction of high‐power electromagnetic waves and magnetized plasmas produces a plethora of fundamental phenomena. Stimulated electromagnetic emissions (SEEs) arises from nonlinear interaction and induces plasma turbulence observable by incoherent scatter radars (ISR). It is important to compare SEE and ISR spectral lines for understanding nonlinear physics in the resonance regime. The SEE‐based methods may provide complimentary diagnostic tools to the traditional ISR theory. In addition, the SEE‐based inversion theory and method is still lacking due to nonlinear wave‐wave and wave‐particle interaction. The physical correlation between SEEs and ISR spectra will provide benefit for better inversion techniques. This work reports experimental observation and parameter inversion of stimulated Brillouin scatter (SBS) at EISCAT (European Incoherent Scatter Radar). We successfully discover similarity between the ISR ion lines and SBS near the third electron gyroharmonic by high power radio waves at EISCAT. A new diagnostic technique based on SEEs have been developed using physical model and an artificial neural network approach. The inversion of SEEs overcomes the non‐Maxwellian limitations on ISR measurements. These observations demonstrate a physical intrinsic correlation between ISR ion and SBS lines, which provides possibilities for developing new inversion techniques based on SBS in comparison with well‐known ISR theory. Key Points Discovery of similarity between high frequency‐induced stimulated Brillouin scattering (SBS) and incoherent scatter radar spectrum Intelligent stimulated electromagnetic emission inversion architecture proposed by incorporating physical insights within an artificial neural network approach Novel ionospheric electron temperature inversion based on SBS and downshifted maximum spectral lines