Annales Geophysicae www.ann-geophys.net 0992-7689 1432-0576 20 1 2002 10.5194/angeo-20-41-2002 http://www.ann-geophys.net/20/41/2002/ http://www.ann-geophys.net/20/41/2002/angeo-20-41-2002.html http://www.ann-geophys.net/20/41/2002/angeo-20-41-2002.pdf 41 55 0000-00-00 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 T. R. Robinson University of Leicester, Leicester, LE1 7RH, UK Correspondence to: T. R. Robinson (txr@ion.le.ac.uk) 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.<br><br><b>Key words. </b>Ionosphere (active experiments; ionospheric irregularities) Radio science (ionospheric propagation)