Statistical and simulation study on the separation in junction frequencies between ordinary (O) and extraordinary (X) wave in oblique ionograms

Abstract

The most important aim in interpreting an oblique ionogram is to obtain the accurate Junction Frequencies (JFs) of the ordinary (O) and extraordinary (X) mode. This requires the correct identification of O- and X-mode traces, so it is very helpful and worthy to grasp the relative position between the two modes. This paper presents a statistical and simulation study of the separation in JFs between O- and X-waves based on observed oblique ionograms over three mid-latitude paths within China and a 3D ray-tracing program. The dependence on local time, season, geomagnetic activity, O-wave JF and group path, solar activity, direction, and length of propagation is investigated. The main conclusions are as follows: (a) the separation on east–west path is susceptible to ionospheric variability, while the separation on north–south path does not show a significant correlation with local time and season; (b) a general diurnal tendency and a summer anomaly on east–west propagation are first proposed and discussed, which may be related to the diurnal variation of hmF2 above the reflection point and the strong lower layers below the reflection point; (c) the separation varies approximately as a cosine function with the propagation direction owning two maxima in the north–south direction and two minima in the east–west direction; (d) the variation patterns of the separation with the propagation length are obviously not the same in different directions. In the case of east–west propagation, the separation decreases to a minimum near ground range of 2000 km and then increases very slowly with increasing ground range, while it monotonically increases for the north–south propagation path.Graphical