Effects of ionospheric irregularities on radio waves—I. Phase path changes

Abstract

The effects of ionospheric irregularities on the phase path of radio waves reflected at vertical incidence are studied using model irregularities. The basic approach used is quite general in that irregularities and background ionospheres of arbitrary shape may be considered. Simple triangular shaped irregularities have been used to demonstrate the application of the method and to illustrate the major effects of irregularities on the phase path. For the ionospheric conditions considered, irregularities below the level X ~ 0.9 have relatively little effect on the phase path of ordinary rays. Irregularities extending above this level produce relatively large effects because the refractive index varies most rapidly near the reflection level. The increased effects of irregularities near the reflection level is not as dramatic in the extraordinary ray case because the refractive index does not change quite as rapidly near the reflection level as it does in the ordinary ray case. When the reflection height is changed by the irregularity the situation is complex because different effects produce opposite changes in the phase path. The result is that an irregularity of a given percentage intensity has its maximum effect on the phase path when it is centred just below the reflection height. The phase path change produced by an irregularity is very dependent on the irregularity intensity and background gradient of the ionosphere but is less sensitive to changes in irregularity thickness. Possible applications of the results to experiments are discussed.