1. Introduction

[2]  Long-distance propagation of HF radio waves in various geophysical conditions has been considered in a large number of publications [see, e.g., Gurevich and Tsedilina, 1979; Kravtsov et al., 1979, and references therein]. The interest in the problem is due, on one hand, to the needs of practical HF radiocommunication and over-horizon radiolocation and, on the other hand, to abilities to study the formation mechanisms of short-wave field at long-distant paths in quiet and disturbed ionosphere. Under natural conditions, there are considerable difficulties in the study of the mechanisms of HF long-distant propagation due to the uncontrolled influence of many factors on the signal characteristics. The total effect of this influence may lead to a very complicated picture of the field formation. We mention here such factors as the presence of the sporadic E layer, traveling ionospheric disturbances (TID), localized disturbances in the regions of particle precipitations, etc.

[3]  In the mid-1970s, the creation of investigation facilities in Russia and the United States to study the impact on the ionospheric plasma by powerful decameter radioemission made it possible to study mechanisms of long-distance HF propagation in controlled conditions. This considerably simplified the problem of separation and identification of various propagation modes. The first experiments on controlling long-distance HF propagation both at fixed frequencies [Getmantsev et al., 1976] and in the wide frequency band of a linearly frequency modulated (LFM) sounder [Uryadov et al., 1995] showed the efficiency of leading radio waves out of the ionospheric wave channel (IWC) due to the scattering at artificial small-scale magnetically oriented irregularities. In these experiments the heating facilities were used to create controlled disturbances at heights of the ionospheric channel. With the development of the national and global network of LFM sounders, it became possible to carry out wide-scale studies of the impact of artificial ionospheric turbulence (AIT) on short-wave propagation.

[4]  In this paper the new results of the study of the AIT influence on the radio wave propagation are presented. The results were obtained using the national and foreign LFM sounders. The AITs were created by the impact on the ionospheric F region of the field of powerful radio waves emitted by the SURA heating facility (Vasil'sursk town, Nizhny Novgorod region, Russia). The diagnostics of AIT was performed by a bistatic Doppler HF radar. The AIT properties were controlled by the artificial radioemission of the ionosphere (ARI). For the properties of ARI, see Frolov et al. [2001, and references therein].

[5]  The experiment was conducted in the period of a magnetic storm. The storm began on 17 August 2003; its various phases covered the entire period of observations. The magnetic storm considerably influenced the results of the experiment. There are a relatively small number of AIT studies in the conditions of magnetic-ionospheric disturbances, and these studies have been conducted mainly on the basis of the heating facilities in Tromsö [Blagoveshchenskaya et al., 1999]. The results of our experiment showed that the HF sounding can be an effective tool of diagnostics of the ionospheric effects of a magnetic storm at F -region heights in the midlatitude ionosphere.