Wave structure of longitudinal variations of night equatorial anomaly

F0F2 longitudinal variations in the night low-latitudinal ionosphere are studied on the ground of data obtained by means of Interkosmos-19 satellite. It is obtained, that in most cases, these variations have a regular wave-like character with ∼ 75 deg longitude period and 2 - 3 MHz average amplitude within the magnetic equator, and 3 - 4 MHz at the anomaly peaks. Longitudinal variations f0F2 at the anomaly peaks are antiphase to those along the magnetic equator. At transition from the anomaly peaks to the average latitudes this wave-like structure step-by-step disappears and is not practically observed at the invariant latitudes over 30 deg. 5 refs., 2 figs