Magneto‐Ionic Triple Splitting of Ionospheric Waves

Abstract

In recent years reports have appeared from various ionospheric observatories concerning the appearance of a third magneto‐ionic component or a so‐called z trace. The phenomenon has also been called magneto‐ionic triple splitting. After having recorded a number of such triple splits at the new Kiruna observatory, we became very interested in the problem as a whole. The entire matter was examined theoretically and as a result it has been possible to show that strong coupling often exists between the ordinary and z components as a critical level. It has further been possible to show that the z wave becomes strongly excited when the collisional frequency v approaches the critical collisional frequency v_c of Appleton and Builder. When v is larger than v_c the o echo rapidly disappears and only the z and x components remain (if v_c is sufficiently small, i.e. at very high latitudes). A useful expression for the transmission coefficient of the o —z wave has been derived.