Effects of multiple scatter on the propagation and absorption of electromagnetic waves in a field-aligned-striated cold magneto-plasma: implications for ionospheric modification experiments

Abstract

Abstract.A new theory of the propagation of low power electromagnetic test waves through the upper-hybrid resonance layer in the presence of magnetic field-aligned plasma density striations, which includes the effects of multiple scatter, is presented. The case of sinusoidal striations in a cold magnetoplasma is treated rigorously and then extended, in an approximate manner, to the broad-band striation spectrum and warm plasma cases. In contrast to previous, single scatter theories, it is found that the interaction layer is much broader than the wavelength of the test wave. This is due to the combined electric fields of the scattered waves becoming localised on the contour of a fixed plasma density, which corresponds to a constant value for the local upper-hybrid resonance frequency over the whole interaction region. The results are applied to the calculation of the refractive index of an ordinary mode test wave during modification experiments in the ionospheric F-region. Although strong anomalous absorption arises, no new cutoffs occur at the upper-hybrid resonance, so that in contrast to the predictions of previous single scatter theories, no additional reflections occur there. These results are consistent with observations made during ionospheric modification experiments at Tromsø, Norway.

EISCAT Svalbard radar observations of SPEAR-induced E- and F-region spectral enhancements in the polar cap ionosphere

“…Morales and Lee, 1977) could give rise to the sporadic E-layer ion line enhancements reported in this paper. These cavitons and the spatial extent of associated density inhomogeneities are consistent with the study by Robinson (2002) who applied a multiple scatter theory to the propagation of electromagnetic test waves during RF-induced heating and found a broadening of the interaction region.…”

First observations of SPEAR-induced artificial backscatter from CUTLASS and the EISCAT Svalbard radars

“…In particular, the so-called "overshoot" phenomenon (Robinson, 1989) regularly seen in non aspect-sensitive scatter is thought to be due to the anomalous absorption (Robinson, 2002) of heater wave power at the UHR due to the relatively slow development of striations there. This quenches the more rapidly developing non aspect-sensitive scatter at the heater reflection height, which is typically a few kilometres above the UHR.…”

Angular dependence of pump-induced bottomside and topside ionospheric plasma turbulence at EISCAT

“…Since striations cause strong anomalous absorption of the HF pump wave [e.g., Stocker et al, 1992;Robinson, 2002], their existence is undesirable if plasma resonance experiments near the higher HF reflection altitude are to be performed. One way to mitigate against pump-induced striations is to employ low duty cycle HF pumping with a low average effective radiated power (ERP).…”