Characteristics of HF Radio Waves Propagation along Subauroral and Mid-latitude Paths over Eastern Siberia during Magnetoactive Period in February 2014

摘要

Based on vertical and oblique-incidence sounding data, we analyzed characteristics of HF propagation during magnetoactive period in February 2014. The oblique-incidence sounding data had been obtained over subauroral and mid-latitude paths: Magadan-Irkutsk, Khabarovsk-Irkutsk, Khabarovsk-Norilsk, and Magadan-Norilsk. The period considered was characterized by a series of solar flares accompanied by intensification of proton and X-ray fluxes as well as by coronal mass ejections. These processes caused two magnetic storms of different intensity. During the main and recovery phases of the first storm, positive ionospheric disturbances were observed in the day. and negative, in the night. During the second magnetic storm, the maximum observed frequencies (MOF) over the Magadan-Irkutsk path fell sharply by 3-5 MHz. Intervals of low MOF values alternated with intervals of absence of reflected signals in ionograms. It specifics that boundaries of the main ionospheric trough could be displaced to the latitude of this path's midpoint. A similar absence of reflected signals in the ionograms was registered over the Khabarovsk-Norilsk path. Besides, during these two storms the oblique sounding ionograms showed additional signals with large time delays over the Magadan-Irkutsk and Khabarovsk-Irkutsk paths in evening and nocturnal hours. The abnormal signals were characterized by strong diffusion and their frequencies considerably exceeded MOF of standard propagation modes. Since the ionosphere is not perfectly horizontally stratified during magnetic storms, signals associated with propagation mode may arrive at a receiving point over a wide range of azimuth angles.