Studying characteristics of the large-scale ionospheric irregularities induced by high-power HF radio emission with GPS diagnosis

Abstract

UDC 533.9 We present the results of experimental studies of artificial large-scale irregularities of the ionospheric electron number density with dual-frequency GPS diagnosis. The total electron content was analyzed in the GPS signal trajectory when the satellites passed over the heated region. Spectral composition of the observed variations was determined by wavelet analysis. Characteristic scales of artificial irregularities of the electron number density in the F layer are estimated. It is experimentally proved that the irregularities remain for at least 15–20 min after the transmitter is switched off. A more confident excitation and increased intensity of the irregularities were also confirmed when the beam was inclined south of the magnetic-zenith direction. When the ionosphere is affected by high-power HF radio emission, electron-density irregularities with sizes from tens of centimeters to tens of kilometers are formed in the region of its reflection [1]. Diagnosis of the large-scale (more than 0.5 km) structure of the ionospheric region disturbed by a high-power radio wave was based on raying the ionosphere by decametric radio emission from space radio sources, aspect scattering of HF and UHF radio waves, raying the heated region by UHF signals of low-orbit and geostationary satellites, satellite radio tomography, and electron density in-situ measurements during the flyby of spacecraft and geophysical rockets through and over the heated region (see [1, 2] and the references cited therein). Large-scale irregularities with scales 5–50 km can also be effectively studied using dual-frequency raying by signals of the Navstar (GPS) or GLONASS microwave satellite systems. During propagation through the heated region, such signals acquire an additional phase increment stipulated by the dispersion of radio waves in the ionospheric plasma and linearly related to the total electron content (TEC) on the propagation trajectory [3, 4]. Since the early eighties, this method has been used to determine the TEC in the ionosphere under natural conditions, and since 2007 the Navstar satellites have intensely been used to determine the total electron content in the ionosphere during the experiments on ionosphere modification by high-power HF radio emission. Such studies were based on the HAARP [5] and Sura [2, 6] facilities. A TEC increase correlated with the ionospheric heating was observed in the daytime experiments [2] and [5]. In [6], where the observations were performed mainly after the sunset with the beam of the Sura facility inclined 12 ◦ south in the geomagnetic meridian plane, both a notable TEC increase in the heated region determined by the angular sizes of the antenna pattern and long-period (10–15 min) TEC variations relative to the average value were recorded. On the basis of obtained results, the authors of [6] made a statement about the manifestation of the magnetic-zenith effect as the most effective impact on the ionosphere in the direction along the geomagnetic field.