Intermediate downshifted maximum of stimulated electromagnetic emission at high‐power HF heating: A new twist on an old problem

Abstract

We report a new spectral feature of Stimulated Electromagnetic Emission (SEE) from the F region ionosphere observed during high‐power HF heating experiments at the SURA and High Frequency Active Auroral Research Program heating facilities. It is located in the SEE spectrum between the pump wave frequency f0 and the well‐known Downshifted Maximum and thus named the Intermediate Downshifted Maximum (IDM). IDM appears at effective radiated powers (ERP) P0≳30 MW and the pump frequencies above electron gyroharmonics, f0−sfce≳1em50 (up to 250) kHz (s = 2, 3, 4). It mirrors the well‐known Upshifted Maximum (UM) relative to f0. The salient stationary and dynamic properties of IDM are described and discussed.

Exploring HF‐induced ionospheric turbulence by Doppler sounding and stimulated electromagnetic emissions at the High Frequency Active Auroral Research Program heating facility

“…According to The SEE spectrogram (Figure 3, bottom) displays the following spectral features: the NC p (the ponderomotive narrow continuum at frequency shifts Δf NC = f 0 À f NC , À10 < Δf NC < 0 kHz), DM (the downshifted maximum at Δf DM ≈ À(10.5-11.5) kHz), and BC (the broad continuum at Δf BC ≈ À(3-40) kHz). Peculiarities of the NC p , DM, and BC are well described in numerous papers [see, e.g., Leyser et al, 1993Leyser et al, , 1994Leyser, 2001;Frolov et al, 2004;Thidé et al, 2005;Sergeev et al, 2006;Grach et al, 2015]. The NC p is called also FNC (fast narrow continuum) in accordance with characteristic time of its development comprising only few milliseconds.…”

“…The prominent SEE spectral features have long been used as indicators of specific nonlinear mode interactions in the altitude region between the reflection z r of the O-mode pump and slightly below the upper hybrid resonance z UH . A number of prominent SEE spectral features have been established from numerous studies of stationary and dynamic SEE spectra performed at the European Incoherent Scatter (EISCAT), Sura, High Frequency Active Auroral Research Program (HAARP), Arecibo, and Space Plasma Exploration by Active Radar (SPEAR) heating facilities for 2.8 < f 0 < 10 MHz [Stubbe et al, 1984;Leyser et al, 1993Leyser et al, , 1994Frolov et al, 2001;Leyser, 2001;Carozzi et al, 2002;Sergeev et al, 2004;Thidé et al, 2005;Sergeev et al, 2006;Kotov et al, 2008;Grach et al, 2008;Norin et al, 2009;Bernhardt et al, 2010Bernhardt et al, , 2011Bordikar et al, 2013;Mahmoudian et al, 2013Mahmoudian et al, , 2014Grach et al, 2015]. The red-shifted (Δf = f À f 0 < 0) SEE features include the narrow continuum (NC) with frequency shifts |Δf| ≈ 0-7 kHz, the downshifted maximum (DM) with |Δf| ≈ 7-20 kHz and its family (2DM, 3DM, etc.…”

Artificial ionospheric layers driven by high‐frequency radiowaves: An assessment

“…shows the bright band around f 0 inFigure 4zoomed to distinguish the SLT signature (NC) from the UH signature (DM) [cf Grach et al, 2015,. …”

Spatiotemporal Characteristics of HF‐Induced Ionospheric Turbulence Revealed by Diagnostic Stimulated Electromagnetic Emission and Test Radio Waves at HAARP

“…25-1.45 MHz is the electron cyclotron frequency. A number of prominent SEE spectral features have been established from numerous studies of stationary and dynamic SEE spectra performed at the European Incoherent Scatter, Arecibo, SURA, and High-frequency Active Auroral Research Program (HAARP) heating facilities (Bernhardt et al, 2010;Frolov et al, 2001;Fu et al, 2013;Grach et al, 2015Grach et al, , 2016Leyser, 2001;Norin et al, 2008Norin et al, , 2009Sergeev et al, 2006Stubbe et al, 1984;Thidé et al, 2005).…”

“…The DSEE methodic was extensively employed at the SURA heating facility (e.g., Frolov et al, 1994;Grach et al, 2015Grach et al, , 2016Norin et al, 2008;Sergeev et al, 1995Sergeev et al, , 1997Sergeev et al, , 1998, 2017Thidé et al, 2005). Note that the concurrent use of QCP, D, and S radiation modes at different frequencies become possible due to sophisticated system of the transmitter control at the HAARP facility.…”