THE IONOSPHERIC TROUGH DYNAMICS IN THE NORTHERN AND SOUTHERN HEMISPHERES - THE LONGITUDINAL AND IMF EFFECT

A study was made of the dynamics of the main ionospheric trough in the northern and southern hemispheres using data of ion density winter me asurements on the Kosmos-900 satellite from 1977 to 1979. Significant longitudinal variations of the trough position have been found which p rove to be different in the different hemispheres: in the northern hem isphere they have the shape of a double wave (period 180 degrees longi tude) with an amplitude of 4-6 degrees of latitude by both day and nig ht whereas, in the southern hemisphere, they exhibit a simple wave (pe riod 360 degrees longitude) with amplitude of about 6 degrees in the n ight hours and 10-12 degrees of latitude in the day hours. The analysi s of the IMF influence on the trough position by day and night has sho wn 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 azimut hal IMF components act in opposite phase while in the southern hemisph ere the effects of the two components are added. Analytic relationship s between the trough shift magnitude and the values of B-Z and B-Y are discussed.