Features of High-Angle Ray Propagation on Paths Crossing the Ionospheric Trough

Abstract

We present the results of experimental study of the features of high-angle ray propagation on subauroral (Magadan — N. Novgorod) and mid-latitude (Khabarovsk — N. Novgorod) chirp-sounding paths crossing the ionospheric trough near its northern and southern boundaries, respectively. The seasonal and diurnal occurrence of a high-angle ray and its frequency range were studied in 1998–2000. It is found that the rate of occurrence of a high-angle ray on the mid-latitude path is maximum in spring and summer. This rate is also maximum in the evening and nighttime hours (19:00–03:00 LT) during all seasons excluding the summer solstice. The diurnal distribution of the rate of occurrence in June is almost uniform. The observed seasonal-diurnal behavior of the rate of occurrence of the high-angle ray is smoother on the subauroral path. The frequency ranges of the high-angle ray on both paths are similar in June, while in winter and spring the frequency range of the high-angle ray on the subauroral path is larger than on the mid-latitude one. We put forward a hypothesis that the different seasonal and diurnal behavior of the occurrence of a high-angle ray and the frequency range of this ray on both paths are stipulated by the features of the formation of a HF-signal field under the influence of two factors, the photoionization and the small-scale stratification of the electron density in the vicinity of the ionospheric trough, which can form a fluctuational waveguide.