ESTIMATE OF THE CONTRIBUTION OF LARGE-SCALE INTERNAL GRAVITY-WAVES AND IMF B-Z COMPONENT NORTHWARD TURNINGS IN LIFTINGS OF THE NIGHTTIME EQUATORIAL IONOSPHERIC F-LAYER DURING MAGNETOSPHERIC DISTURBANCES

An attempt is made to separate the causes of night-time equatorial F-layer strong liftings observed during magnetospheric disturbances. These liftings may be caused by the well-known disturbances in electrodynamical plasma drift under the IMF B-z component northward turnings. The other lifting mechanism is associated with large-scale internal gravity waves (IGW) which are generated by the auroral electrojets and then travel to the equator. These two mechanisms are often superposed. In order to separate their effects, a big amount of sounding data has been analysed along with data on drifts measured at the equatorial station Jicamarca and other helio-geophysical data. The data indicate that large-scale IGW can cause significant lifting of the night-time equatorial F-layer. This effect is observed independently of B, behaviour at this time. In those occasions when IGW arrival at the equatorial latitudes coincides in time with B, northward turning, action of these two mechanisms adds to each other, and their total effect is stronger than the effect of each of them separately.