<1> The causes of longitudinal and latitudinal variations in the F2-layer maximum in the summer nighttime ionosphere at middle, subauroral, and auroral latitudes are investigated. To do this the following problems are solved in sequence. The longitudinal variations in hmF2 are studied in the belt of invariant latitudes between 40¿ and 65¿ according to the Intercosmos 19 satellite data. It is shown that the longitudinal effect in the quiet ionosphere is rather stable but differs by its character in the Southern and Northern hemispheres. Considerable discrepancies between Intercosmos 19 data and International Reference Ionosphere (IRI) model are detected at high latitudes. On the basis of the longitudinal variations in hmF2 using the servo model of the ionosphere and the Mass Spectrometer Incoherent Scatter thermosphere model, variations in the vertical drift velocity, W, caused by neutral wind are calculated. In terms of the Tikhonov regularization method, the approach to a solution of the inverse problem on deriving meridional and zonal components of the neutral wind from the longitudinal variations in W is developed. A comparison with the Horizontal Wind Model (HWM) neutral wind model is performed and an attempt to correct this model for the considered conditions is made. Estimation of the contribution of the neutral wind, composition and temperature into longitudinal and latitudinal variations in hmF2 is performed. The causes of the asymmetry between the Northern and Southern hemispheres are discussed.