The ionospheric trough dynamics in the northern and southern hemispheres: the longitudinal and IMF effect

Abstract A study was made of the dynamics of the main ionospheric trough in the northern and southern hemispheres using data of ion density winter measurements on the Kosmos-900 satellite from 1977 to 1979. Significant longitudinal variations of the trough position have been found which prove to be different in the different hemispheres: in the northern hemisphere they have the shape of a double wave (period 180° longitude) with an amplitude of 4–6° of latitude by both day and night whereas, in the southern hemisphere, they exhibit a simple wave (period 360° longitude) with amplitude of about 6° in the night hours and 10–12° of latitude in the day hours. The analysis of the IMF influence on the trough position by day and night has shown both B Z and B Y to affect the shift of the ionospheric trough. It has been found that in the northern hemisphere the vertical and azimuthal IMF components act in opposite phase while in the southern hemisphere the effects of the two components are added. Analytic relationships between the trough shift magnitude and the values of B Z and B Y are discussed.