ANALYTIC CALCULATION OF THE ORDINARY (O) AND EXTRAORDINARY (X) MODE NOSE FREQUENCIES ON OBLIQUE IONOGRAMS

On oblique ionograms, the maximum frequencies of the ordinary and extr aordinary modes are referred to as nose frequencies. The difference in the nose frequencies depends on parameters such as the length of the propagation circuit and the direction of propagation. In this paper, t he difference in nose frequencies is studied using the frequency scali ng technique of BENNETT et al. [(1991) Appl. Comput. Electromagn. Soc. Jl 6, 192]. For long paths, an explicit formula is obtained which giv es the difference approximately as a function of the local magnetic di p and azimuth of propagation at the ray mid point. For shorter paths, it is shown how analytic ray tracing can be used to determine the diff erence.