Can ionospheric refraction and oblique reflection explain the Canadian 50 MHz IGY radio aurora observations?

Abstract

Uspensky and Williams (1988) have recently suggested that the aspect sensitivity of the radio aurora is universally near 10 dB/deg. They have further suggested that the Canadian measurement of 1–2 dB/deg at 48 MHz can be understood by correctly accounting for E region ionospheric refraction and oblique reflection in the case of equatorward directed radio waves. This hypothesis has an attractive simplicity. Moorcroft (1989) has subsequently proposed refraction by tilted layers to explain a number of puzzling features of Canadian Bistatic Auroral Radar System (BARS) data. We have therefore made an examination of the ionospheric conditions necessary to enable refraction/reflection to explain the Canadian International Geophysical Year (IGY) observations and have compared them with those expected in the E region ionosphere. It is established that refraction in extended and uniform E region plasma layers is insufficient to explain these observations using the Uspensky and Williams hypothesis. On the other hand, it may be possible that oblique reflection in a thin, dense, and localized sporadic E structure is sufficient to support the hypothesis. More information about these structures is required before a definitive conclusion can be drawn. The properties necessary for these structures to be consistent with an universal aspect sensitivity of about 10 dB/deg are presented.