First observations of electron gyro-harmonic effects under X-mode HF pumping the high latitude ionospheric F-region

Abstract

Abstract. We provide the first experimental evidence of the sensitivity of phenomena induced 26 by extraordinary (X-mode) polarized HF high power radio waves to pump frequency stepping 27 across the fifth electron gyro-harmonic (5fce) from below to above. The results were obtained at 28 the EISCAT (European Incoherent Scatter Scientific Association) HF heater facility near Tromsø 29 under effective radiated powers of 456 -715 MW, when the HF pump wave was transmitted into 30 the magnetic zenith. We have analyzed the behavior and intensities of various spectral lines in 31 the narrowband stimulated electromagnetic emission (SEE) spectra observed far from the heater, 32 HF-enhanced plasma and ion lines (HFPL and HFIL) from EISCAT UHF incoherent scatter 33 radar spectra, and artificial field-aligned irregularities from CUTLASS (Co-operative UK Twin 34 Located Auroral Sounding System) observations, depending on the frequency offset of the pump 35 field relative to the 5fce. At pump frequencies below 5fce the narrowband SEE spectra exhibited 36 very intense so-called stimulated ion Bernstein scatter (SIBS), accompanied by other spectral 37 components, associated with stimulated Brillouin scatter (SBS), which are greatly suppressed 38 and disappeared in the vicinity of 5fce and did not reappear at fH > 5fce. As the pump frequency 39 reached 5fce, the abrupt enhancements of the HFPL and HFIL power, the appearance of cascade 40 lines in the plasma line spectra, and the onset of increasing CUTLASS backscatter power 41 occurred. That is opposite to the ordinary mode (O-mode) effects in the vicinity of 5fce. The X-42 mode pumping at frequencies below and in the vicinity of the fifth electron gyro-harmonic 43 clearly demonstrated an ascending altitude of generation of induced plasma and ion lines from 44 the initial interaction height, whereas for O-mode heating the region of interaction descended. 45The observations are consistent with the coexistence of the electron acceleration along and 46 across the geomagnetic field at fH < 5fce, while only very strong electron acceleration along the 47 magnetic field was observed at fH ≥ 5fce. 48 49

Distinctive Features of Langmuir and Ion‐Acoustic Turbulences Induced by O‐ and X‐Mode HF Pumping at EISCAT

“…As shown by Blagoveshchenskaya et al (2014Blagoveshchenskaya et al ( , 2015, the HFPLs and HFILs were generated through the whole X-mode transmission pulse at various high heater frequencies both below and above the critical frequency of the F 2 layer (f H ≤ f o F 2 and f o F 2 < f H ≤ f o F 2 + f ce /2, where f ce is the electron gyroharmonic frequency). In the course of the X-mode HF pumping experiments, the excitation of Langmuir and ion-acoustic plasma waves was accompanied by the generation of artificial small-scale FAIs (Blagoveshchenskaya et al, 2011(Blagoveshchenskaya et al, , 2013(Blagoveshchenskaya et al, , 2015, very strong radio-induced optical emissions in red and green lines (Blagoveshchenskaya et al, 2014), and the narrowband stimulated electromagnetic emission within 1 kHz of the heater frequency recorded at a distance of 1,200 km from the EISCAT/Heating facility (Blagoveshchenskaya et al, 2015;Blagoveshchenskaya, Borisova, Kalishin, et al, 2017).…”

Aspect dependence of Langmuir parametric instability excitation observed by EISCAT

“…Here we present two X-mode heating experiments operated on 21 and 22 October 2012, which provide evidence to survey the aspect dependence of PI excited by X-mode EM heating wave. These two experiments were performed by the Russian team to study the X-mode HF heater-induced phenomena in the F region of the ionosphere [Blagoveshchenskaya et al, 2015[Blagoveshchenskaya et al, , 2017. The EISCAT UHF radar is able to observe the Langmuir wave and ion acoustic wave (IAW) propagated along the radar beam.…”

“…Although X-mode heating effects have been discussed by many researchers, until recently, Blagoveshchenskaya et al [2011Blagoveshchenskaya et al [ , 2013Blagoveshchenskaya et al [ , 2014Blagoveshchenskaya et al [ , 2015Blagoveshchenskaya et al [ , 2017 reported the direct evidence of PI excitation by using the European Incoherent Scatter (EISCAT) observations. During X-mode heating experiments, a great number of nonlinear phenomena are observed, such as small-scale field-aligned irregularities [Blagoveshchenskaya et al, 2011[Blagoveshchenskaya et al, , 2013[Blagoveshchenskaya et al, , 2015, enhanced airglow [Blagoveshchenskaya et al, 2014], narrowband SEEs [Blagoveshchenskaya et al, 2015].…”

Stimulated electromagnetic emissions spectrum observed during an X-mode heating experiment at the European Incoherent Scatter Scientific Association

“…These results suggested that the narrow SEE spectra may be associated with the ion acoustic wave, electrostatic ion cyclotron wave, and electrostatic ion cyclotron harmonic wave. Blagoveshchenskaya et al () demonstrated experimental results on the behavior and intensities of various spectral lines in the narrowband SEE spectra within 1 kHz of the heater frequency, depending on the pump frequency stepping across the fifth electron gyroharmonic frequency observed far away from the heater frequency. Blagoveshchenskaya et al () analyzed in detail the narrowband SEE spectral features in the course of the X‐mode experiment on February 25, 2013, at a pump frequency of 5.423 MHz at Saint Peterburg, which is 1,200 km away from Tromsø.…”

“…Blagoveshchenskaya et al () analyzed in detail the narrowband SEE spectral features in the course of the X‐mode experiment on February 25, 2013, at a pump frequency of 5.423 MHz at Saint Peterburg, which is 1,200 km away from Tromsø. However, Blagoveshchenskaya et al (), , did not observe any spectral features within 200 kHz near Tromsø that were associated with X‐mode heating near the fourth gyroharmonic frequency.…”