Ion gyroharmonic structures in stimulated radiation during second electron gyroharmonic heating: 1. Theory

Abstract

[1] Stimulated electromagnetic emissions (SEEs) may provide important diagnostic information about space plasma composition, energetics, and dynamics during active experiments in which ground-based high-powered radio waves are transmitted into the ionosphere. The nonlinear plasma processes producing this secondary radiation are not well understood particularly for some recent observations where the transmitter (pump) frequency is near the second harmonic of the electron gyrofrequency. New, more comprehensive, experimental observations of spectral features within 1 kHz of the pump wave frequency are reported here to begin more careful comparisons of the experimental observations and a possible theoretical underpinning, which is also provided. The experimental observations typically show two distinct types of secondary radiation spectra, which are (a) discrete narrowband harmonic spectral structures ordered by the ion gyrofrequency and (b) broadband spectral structure with center frequency near 500 Hz and similar spectral bandwidth. A theoretical model is provided that interprets these spectral features as resulting from parametric decay instabilities in which the pump field ultimately decays into high-frequency upper hybrid/electron Bernstein and low-frequency neutralized ion Bernstein and/or obliquely propagating ion acoustic waves at the upper hybrid interaction altitude. Detailed calculations of the threshold level, growth rate, unstable wave number, and frequency bandwidth of the instabilities are provided for comparisons with experimental observations. An assessment of the effect of the critical instability parameters are provided including pump electric field strength, proximity of the pump frequency to the electron gyrofrequency and pump electric field geometry. The model shows quite reasonable agreement with the experimental observations. Further discussions are provided of connections with past observed SEE spectral features and potential new diagnostic information provided by these newly categorized spectra.Citation: Samimi, A., W. A. Scales, H. Fu, P. A. Bernhardt, S. J. Briczinski, and M. J. McCarrick (2013), Ion gyroharmonic structures in stimulated radiation during second electron gyroharmonic heating: 1. Theory, J. Geophys.

Ion gyro‐harmonic structuring in the stimulated radiation spectrum and optical emissions during electron gyro‐harmonic heating

“…[15] Discrete narrowband spectral features within 1 kHz of the pump frequency separated by multiples of the ion gyro-frequency f ci observed in the SEE spectrum have been attributed to the simultaneous parametric decay of upper hybrid/electron Bernstein waves into multiple upper hybrid/electron Bernstein and ion Bernstein waves , Samimi et al, 2012a, 2012b. As stated in section 1, this process will be referred to here as Stimulated Ion Bernstein SIB Scatter (SIBS) .…”

“…Recent studies at the High Frequency Active Auroral Research Program (HAARP) facility, showed new SEE spectral features within 1 kHz of the pump frequency due to so-called Stimulated Ion Bernstein Scatter (SIBS) during pump heating near the second electron gyro-harmonic 2f ce Scales et al, 2011;Samimi et al, 2012aSamimi et al, , 2012b. SEE spectral structures ordered by harmonics of the ion gyro-frequency f ci (near 50 Hz) were observed.…”

“…Emissions for f 0 2f ce [23] The SIBS for heating at 2f ce was first investigated for a broad range of pump parameters by Samimi et al [2012b]. During the 2012 campaign a set of experiments was dedicated to a more detailed study of SIBS with pump frequency sweeping through 2f ce and 3f ce .…”

“…A broadband spectral feature, within 1 kHz of pump frequency was observed during heating near 2f ce on occasion as well [Samimi et al, 2012a[Samimi et al, , 2012b. A new theory based on the interaction at the UH altitude, where the pump frequency equals the local UH frequency, was developed by Samimi et al [2012aSamimi et al [ , 2012b which not only was able to explain the ion gyro-structures as a result of SIBS decay process but also predicted the oblique IA decay process as a possible source responsible for broadband spectral features observed in the experiment. The capability of SEE features in predicting irregularities generated during heating experiments can be employed to investigate the generation mechanism and plasma waves involved for other associated processes such as artificial optical emissions.…”

Stimulated Brillouin scattering in magnetized plasmas

“…The scattering by ion-cyclotron waves (e.g. Shukla and Tagare 1979;Samimi A. et al 2013) and drift waves (Shukla et al 1984) can then be important. Related experiments have later been outlined for piezoelectric semiconductor plasmas (e.g.…”