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

Abstract

High‐power ordinary mode radio waves produce artificial ionization in the F region ionosphere at the European Incoherent Scatter (Tromsø, Norway) and High Frequency Active Auroral Research Program (Gakona, Alaska, USA) facilities. We have summarized the features of the excited plasma turbulence and descending layers of freshly ionized (“artificial”) plasma. The concept of an ionizing wavefront created by accelerated suprathermal electrons appears to be in accordance with the data. The strong Langmuir turbulence (SLT) regime is revealed by the specific spectral features of incoherent radar backscatter and stimulated electromagnetic emissions. Theory predicts that the SLT acceleration is facilitated in the presence of photoelectrons. This agrees with the intensified artificial plasma production and the greater speeds of descent but weaker incoherent radar backscatter in the sunlit ionosphere. Numerical investigation of propagation of O‐mode waves and the development of SLT and descending layers have been performed. The greater extent of the SLT region at the magnetic zenith than that at vertical appears to make magnetic zenith injections more efficient for electron acceleration and descending layers. At high powers, anomalous absorption is suppressed, leading to the Langmuir and upper hybrid processes during the whole heater on period. The data suggest that parametric upper hybrid interactions mitigate anomalous absorption at heating frequencies far from electron gyroharmonics and also generate SLT in the upper hybrid layer. The persistence of artificial plasma at the terminal altitude depends on how close the heating frequency is to the local gyroharmonic.

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

“…In the course of the pump pulse from 13:46 to 13:56 UT the background ionosphere enhanced and reflection altitudes decreased. This has nothing to do with descending structures observed at the EISCAT/heating and HAARP under O‐mode pumping, which were reported and discussed by Dhillon and Robinson (), Ashrafi et al (), Pedersen et al (), and Mishin et al (). However, such descending ion line backscatter was observed at O‐mode pumping at 7.1 and 5.423 MHz on 21 February 2013 and could be clearly recognized from Figures and in section 2.…”

Creating space plasma from the ground

“…One model called the Quasilinear Zakharov model [ Sanbonmatsu et al ., ; Myatt et al ., ] can model 10 km or greater plasma layers near HF reflection in 2‐D simulations and hundreds of meters in 3‐D simulations with current parallel computing capabilities. Theoretical studies of late time phenomena [ Gurevich et al ., ] and work related to the HAARP ionization layers [ Eliasson et al ., ; Mishin et al ., ] have aided our understanding of the interaction of suprathermal electrons with the ionosphere. However, the detailed physics behind the electron acceleration at late times greater than ~10 ms at Arecibo remains somewhat elusive.…”

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

“…The bottom IA layer was observed near the 480 reflection altitude of the extraordinary polarized powerful HF radio wave, whereas the top IA 481 layer was 12 km above the bottom one. All these features mentioned above can be produced by 482 burned out collapsing cavities and the heat flux-driven instability (Mishin et al, 2016). the ionosphere is an inhomogeneous and dispersive medium.…”