Artificial small-scale field-aligned irregularities in the high latitude F region of the ionosphere induced by an X-mode HF heater wave

Abstract

[1] The effects on the high-latitude F region of the ionosphere by X-mode powerful HF radio waves injected towards the magnetic zenith (MZ) are analysed. The experiments were conducted using the EISCAT/Heating facility and UHF radar at Tromsø, Norway, the CUTLASS (SuperDARN) radar and the EISCAT ionosonde (dynasonde). The results show that the X-mode HF pump wave, radiated into the magnetic zenith from the HF heater, can generate very strong small-scale artificial field aligned irregularities (AFAIs) in the F-region of the high-latitude ionosphere. These irregularities, with spatial scales across the geomagnetic field of the order of 8-15 m, are generated when the heater frequency is above the ordinary-mode critical frequency but comparable with the extraordinary-mode critical frequency. The generation of the X-mode AFAIs was accompanied by electron temperature (Te) enhancements up to 50% above the background level and an increase in the electron density (Ne) by up to 30%.

The behavior of electron density and temperature during ionospheric heating near the fifth electron gyrofrequency

“…Blagoveshchenskaya et al . [, ] reported EISCAT UHF radar observation of an increase up to 30% in electron density over a wide altitude range induced by an X mode pump wave with frequency f HF ≈ f x F 2 , where f x F 2 is the critical frequency of the extraordinary wave for F 2 region. Senior et al .…”

“…The enhancements in N e / N e 0 presented in Figure have similarities to that given by Blagoveshchenskaya et al . [, ], Senior et al . [], and Borisova et al .…”

Comment on “Parametric Instability Induced by X‐Mode Wave Heating at EISCAT” by Wang et al. (2016)

“…The growing body of X‐mode experiments at the EISCAT (European Incoherent Scatter) Scientific Association HF heating facility with the use of various multi‐instrument diagnostics showed that extraordinary (X‐mode) powerful HF radio waves are capable of producing a strong modification of the high latitudinal ionospheric F region, including the generation of the artificial field‐aligned irregularities (FAIs) (Blagoveshchenskaya, Borisova, Yeoman, Rietveld, ; Blagoveshchenskaya, Borisova, Yeoman, Rietveld, Ivanova, et al, ; Blagoveshchenskaya et al, ), optical emissions at red (630 nm) and green (557.7 nm) lines (Blagoveshchenskaya et al, ), and various spectral components in the narrowband stimulated electromagnetic emission spectra (Blagoveshchenskaya et al, ). Considerable study has been given to the HF‐enhanced ion and plasma lines (HFILs and HFPLs) from the EISCAT UHF incoherent scatter radar spectra excited under X‐mode heating, which are the signatures of the ion acoustic (IA) and Langmuir (L) electrostatic waves (Blagoveshchenskaya et al, , ).…”

Optical and ionospheric phenomena at EISCAT under continuous X‐mode HF pumping

“…However, recent experimental data, obtained at the EISCAT (European Incoherent Scatter Scientific Association) HF heating facility, demonstrate that an X ‐polarized HF pump wave can also produce the artificial field‐aligned irregularities (FAI), HF‐enhanced ion, and plasma lines (HFIL and HFPL) in the EISCAT UHF radar spectra. The phenomena mentioned above were generated in the underdense ionosphere in the frequency band f x F 2 ≥ f H > f o F 2 for any heater frequencies in the range f H = 4–8 MHz, where O ‐mode effects cannot be excited at all [ Blagoveshchenskaya et al ., , ]. In addition, only for the higher heater frequencies ( f H > 6 MHz) can the HFIL and HFPL also be excited even in the overdense ionosphere, f H < f o F 2 [ Senior et al ., ].…”