INTERNATIONAL JOURNAL OF GEOMAGNETISM AND AERONOMY VOL. 5, GI3009, doi:10.1029/2004GI000081, 2005

Electron collision frequency and HF waves attenuation in the ionosphere

N. P. Danilkin
Institute of Applied Geophysics, Moscow, Russia

P. F. Denisenko, B. G. Barabashov, and G. G. Vertogradov
Institute of Physics, Rostov on Don State University, Rostov on Don, Russia

Abstract

[1] The results of the studies of the effective electron collision frequency and HF wave attenuation in the midlatitude ionosphere carried out in the Rostov-on-Don University during the past 35 years are presented. It is found that (besides the collision absorption) the attenuation is determined also by additional dissipative and nondissipative mechanisms. The absorption is reliably determined using the gas-kinetic model of the effective electron collision frequency. The additional dissipation mechanism (anomalous absorption of ordinary waves) may occur because of their statistical transformation into slow extraordinary waves at the scattering at small-scale fluctuations of the electron concentration. The only cause of the nondissipative attenuation is the small-angle multiple forward scattering at large-scale irregularities of the ionospheric plasma. At signal propagation in the vicinity of the maximum usable frequency (MUF) the scattering provides an input into the attenuation comparable to the collision absorption. At the illumination of the ionosphere by a point source from the Earth surface, the multiple scattering leads to such distribution of the field at which the emission reflected under small angles to the vertical has an energy deficit. Presence of addition (to the collision) absorption mechanisms of HF waves attenuation leads to overestimated (as compared to the gas-kinetic ones) estimates of the electron collision frequency. The determination of the physical nature of the attenuation made it possible to develop correct methods of modeling of HF radio waves propagation in the three-dimensional inhomogeneous magnetically active ionospheric plasma and test these methods in a vast series of experiments.

Received 24 August 2004; revised 11 January 2005; accepted 1 March 2005; published 30 June 2005.

Keywords: Electron collision frequency; Attenuation of HF radiowaves; Physics of the lower ionosphere.

Index Terms: 2487 Ionosphere: Wave propagation; 2494 Ionosphere: Instruments and techniques; 2439 Ionosphere: Ionospheric irregularities.

Citation: Danilkin, N. P., P. F. Denisenko, B. G. Barabashov, and G. G. Vertogradov (2005), Electron collision frequency and HF waves attenuation in the ionosphere, Int. J. Geomagn. Aeron., 5, GI3009, doi:10.1029/2004GI000081.