HF wave scattering by field‐aligned plasma irregularities considering refraction in the ionosphere

Abstract

[1] This paper analyzes the effect of ionospheric refraction on the scattering of high frequency (HF) signals by random field-aligned irregularities in the upper ionosphere. Ray optics calculations are made using the perturbation method for a plane-stratified (on average) ionosphere, i.e., the incident and scattered waves are both supposed to propagate along the undisturbed trajectories with neglect of the geomagnetic field effect. The equation for the so-called cone of aspect-sensitive scattering is derived to relate the trajectory characteristics of the incident and aspect-sensitive scattered signals. The Born approximation is applied to calculate the scattering cross-section for the anisotropic power law model spectrum of random irregularities of the upper ionosphere. The possibility of excitation of the ionospheric interlayer waveguide by the aspect-sensitive scattered HF signals is analyzed in detail for the specific conditions of the HF heating experiment at European Incoherent Scatter (EICSAT).

Physical mechanisms associated with long‐range propagation of the signals from ionospheric heating experiments

“…Introduction of the ground scattering mechanism of the long-range propagation of the heater's signals changes the general perception of the effect observed by Zalizovski et al [2009]. Note that self-scattering in the sense that was assumed in earlier publications [Zalizovski et al, 2009;Galushko et al, 2013] is no longer required to explain the effect. Scattering by natural ionospheric irregularities may be sufficient to explain the spectral broadening of one of the two signal components, and ionospheric scattering is not necessary to explain the long-range propagation.…”

“…Realization of this fact served as an incentive for our work. This paper, similar to Galushko et al [2013], considers in detail only one aspect of the effect described in Zalizovski et al [2009]. We suggest an alternative, more adequate mechanism that enables long-range propagation of the wideband component of the signal: scattering of the main beam, after its return from the ionosphere, by the mountain relief in the vicinity of the heater.…”

“…[]. Authors of a recent publication [ Galushko et al ., ] made an attempt to relate the two arguing a theoretical possibility that self‐scattering (treated by them as single scattering) was responsible for feeding the ionospheric waveguide by a portion of the heater's main beam radiation at conditions of the EISCAT Tromsø experiment [ Zalizovski et al ., ] thus enabling observations of the scattered component at superlong ranges. However, this attempt is flawed in several respects.…”

“…First, the approximation of isotropic plasma used in Galushko et al . [] is too crude for their type of estimates heavily relying on raypath shapes in the conditions when the ratio between the radio frequency, and the electron gyrofrequency is only 2.7. The authors provide mainly geometrical considerations and do not evaluate absolute energetic effectiveness of the single‐scattering and channeling processes.…”

“…The self-scattering does happen to the near-vertically propagating powerful HF radiation, and therefore, it is not specific to the effect observed by Zalizovski et al [2009]. Authors of a recent publication [Galushko et al, 2013] made an attempt to relate the two arguing a theoretical possibility that self-scattering (treated by them as single…”