Stimulated Brillouin scattering during electron gyro-harmonic heating at EISCAT

H Y Fu,T K Yeoman,S J Briczinski,A Senior,J M Ruohoniemi,W A Scales,M T Rietveld,P A Bernhardt,M J Kosch

doi:10.5194/angeo-33-983-2015

Abstract

Abstract. Observations of secondary radiation, stimulated electromagnetic emission (SEE), produced during ionospheric modification experiments using ground-based, high-power, high-frequency (HF) radio waves are considered. The High Frequency Active Auroral Research Program (HAARP) facility is capable of generating narrowband SEE in the form of stimulated Brillouin scatter (SBS) and stimulated ion Bernstein scatter (SIBS) in the SEE spectrum. Such narrowband SEE spectral lines have not been reported using the European Incoherent Scatter (EISCAT) heater facility before. This work reports the first EISCAT results of narrowband SEE spectra and compares them to SEE previously observed at HAARP during electron gyro-harmonic heating. An analysis of experimental SEE data shows observations of emission lines within 100 Hz of the pump frequency, interpreted as SBS, during the 2012 July EISCAT campaign. Experimental results indicate that SBS strengthens as the pump frequency approaches the third electron gyro-harmonic. Also, for different heater antenna beam angles, the CUTLASS radar backscatter induced by HF radio pumping is suppressed near electron gyro-harmonics, whereas electron temperature enhancement weakens as measured by EISCAT/UHF radar. The main features of these new narrowband EISCAT observations are generally consistent with previous SBS measurements at HAARP.

Highlights

Ionospheric plasma turbulence can be created by injection of powerful high-frequency (HF) radio waves from groundbased transmitters
Electromagnetic backscattered waves were produced by the European Incoherent Scatter (EISCAT) HF transmitter operating with an effective radiated power (ERP) of 148 MW for the magnetic zenith beam
Strong emissions downshifted by ∼ 8 Hz and upshifted by ∼ 12 Hz in the spectra are clearly observed in Fig. 1 with power within 10 dB relative to the reflected pump wave

Summary

Introduction

Ionospheric plasma turbulence can be created by injection of powerful high-frequency (HF) radio waves from groundbased transmitters. Stimulated Brillouin scattering (SBS) has been recently observed in the high-power, HF wave ionospheric experiments, shifted by a few tens of hertz from the pump. Mahmoudian et al (2013b) investigated the threshold for SBS at HAARP and experimentally showed that an effective radiated power (ERP) ∼ 140 MW is required to excite SBS associated with ion acoustic (IA) waves. These observations motivated this campaign at EISCAT to produce SBS using lower-power HF heating.

Experiment setup

Narrowband SEE observations

Associated wideband SEE and irregularities

Discussion and conclusions