A. G. Bronin

RADIATIVE TRANSFER IN A LAYER OF MAGNETIZED PLASMA WITH RANDOM IRREGULARITIES

Abstract The problem of radio wave reflection from an optically thick plane uniform layer of magnetized plasma is considered in the present work. The plasma electron density irregularities are described by a spatial spectrum of arbitrary form. The small-angle scattering approximation in invariant ray coordinates is proposed as a technique for the analytical investigation of the radiation transfer equation. The approximate solution describing the spatial and angular distribution of radiation reflected from a plasma layer is obtained. The solution obtained is investigated numerically for the case of ionospheric radio wave propagation. Two effects occur as a consequence of multiple scattering: a change in the reflected signal intensity and an anomalous refraction.The problem of radio wave reflection from an optically thick plane monotonous layer of magnetized plasma is considered at present work. The plasma electron density irregularities are described by spatial spectrum of an arbitrary form. The small-angle scattering approximation in the invariant ray coordinates is suggested for analytical investigation of the radiation transfer equation. The approximated solution describing spatial-and-angular distribution of radiation reflected from a plasma layer has been obtained. The obtained solution has been investigated numerically for the case of the ionospheric radio wave propagation. Two effects are the consequence of multiple scattering: change of the reflected signal intensity and anomalous refraction.

Anomalous attenuation of extraordinary waves in ionosphere heating experiments

Multiple scattering from artificial random irregularities HF-induced in the ionosphere F region causes significant attenuation of both ordinary and extraordinary radio waves together with the conventional anomalous absorption of ordinary waves due to their conversion into the plasma waves. To study in detail features of this effect, purposeful measurements of the attenuation of weak probing waves of the extraordinary polarization have been performed at the Sura heating facility. Characteristic scale lengths of the involved irregularities are ~0.1-1 km across the geomagnetic field lines. To determine the spectral characteristics of these irregularities from the extraordinary probing wave attenuation measurements, a simple procedure of the inverse problem solving has been implemented and some conclusions about the artificial irregularity features have been drawn. Theory and details of experiments have been stated earlier. This paper reports results of two experimental campaigns carried out in August 2000 and June 2001 under support of Russian Foundation for Basic Research (grants No. 99-02-17525 and No. 01-02-31008). Particularity of these experiments consisted in using of lower heating power (20-80 MW ERP). Regular character of the multiple scattering effects has been confirmed.Multiple scattering of radio waves by artificial random irregularities HF-induced in the ionosphere F region may cause significant attenuation of both ordinary and extraordinary waves together with common anomalous absorption of ordinary waves due to their non-linear conversion into plasma waves. To demonstrate existence and strength of this effect, direct measurements of attenuation of both powerful pump wave and weak probing waves of extraordinary polarization have been carried out during an experimental campaign on September 6, 7 and 9, 1999 at the Sura heating facility. The attenuation magnitude of extraordinary waves reaches of 1-10 dB over a background attenuation caused by natural irregularities. It is interpreted in the paper on the base of the theory of multiple scattering from the artificial random irregularities with characteristic scale lengths of 0.1-1 km. Simple procedure for determining of irregularity spectrum parameters from the measured attenuation of extraordinary waves has been implemented and some conclusions about the artificial irregularity formation have been obtained.

Group propagation time of quasi-monochromatic radiation in a plane layer of plasma with random irregularities

The influence of multiple scattering in a plasma layer with random irregularities on the propagation time of a totally reflected pulse signal has been considered. Two approaches have been implemented. The first one is based on an analytical solution of the radiative transfer equation. The second one is based on a numerical simulation in the spirit of the Monte Carlo technique. The general conclusion is that, subject to relative position of a transmitter and a receiver and the irregularity shape, one can observe both a decrease and an increase of the propagation time in comparison with the reflection from the same layer deprived of random irregularities. The numerical estimates made in this paper regard the case of radio sounding of the ionospheric plasma. It has been shown that the magnitude of the considered effect is of the order of the characteristic pulse length applied in the ionosphere vertical sounding.

On the theory of anomalous absorption of an ordinary wave

We obtain and analyze numerically exact formulas for anomalous absorption of a probing ordinary wave due to its transformation into plasma waves under vertical sounding of an ionospheric plasma layer with given spectrum of irregularities. The nature of possible approximations and their validity limits are analyzed.

Reduction of radiation-transport equation to invariant variables for randomly inhomogeneous plano-stratified magnetoactive plasma

ConclusionIt has been shown that the geometrical-optical radiation-energy balance in a plano-stratified layer is a strict mathematical consequence of the energy-transport equation. Its representation in invariant variables provides a number of advantages, which have been discussed in detail [3].

Statistical characteristics of polarization of pulse signals in vertical probing of the ionosphere

In the model of equatorial bubbles (2)-(6), the effects of plasma diamagnetism are taken into account. The results of numerical experiments show that the gradient plasma drift and related diamagnetic currents have no marked effect on the dynamics and structure of RayleighTaylor inhomogeneities greatly extended along the field lines, for both the linear and nonlinear stages of development. The action of the gradient drift is manifested only in the formation of the structure of the current cells. For the boundary conditions (7) and (8), eliminating the local frequency of solutions of system (2)-(6), the diamagnetic current in the region of integration forms a structure in the shape of Greek letter g. This current flows into the region occupied by the inhomogeneity in the west, flows around it in a clockwise direction, and flows out in the east. Disregarding the diamagnetism, the current lines are practically parallel to the y-axis.

Collisionless damping of ordinary electromagnetic waves in the ionospheric plasma with power spectrum of inhomogeneities

Collisionless absorption of ordinary waves in the ionosphere is considered due to scattering into the z-mode from random inhomogeneities in the resonance region. The non-Hermitian components of the effective dielectic permeability tensor are determined for an isotropic power spectrum with an exponential index of 2, and for a model of infinitely extended irregularities with a power spectrum exponential index of 2-4. The anomalous absorption of vertically probing ordinary waves is calculated for the irregularity spectra described above, as well as for a power spectrum with exponential index of 4.

Dielectric properties of a collisionless magnetoactive plasma with a power-law spectrum of random inhomogeneities

The dielectric properties of a randomly inhomogeneous magnetoactive plasma are investigated in the present study under conditions of extraordinary wave resonance. The electron concentration inhomogeneities are characterized by a spatial spectrum of the form r ~ (p2 + km2)-2 exp (-p2s where k m = 2~/L, with s and L being the minimum and maximum inhomogeneity scales. For s << L the spectrum has a power-law shape over a wide range of wave numbers. Taking into account spatial dispersion, the anti-Hermitian components of the effective dielectric permittivity are calculated.