[2] Currently, there exist a few versions of empirical models of the lower ionosphere in this or that way taking into account the dependence of the electron concentration ( ne ) at 60-90 km on solar and geomagnetic activity, latitude, season, and local time [Belikovich et al., 1983; Bilitza, 1990; Bremer and Singer, 1977; Danilov and Ledomskaya, 1983; Danilov et al., 1991; Chasovitin, 1983; Friedrich and Torkar, 1992, 2001\linkfrie01; Knyazev et al., 1993; McNamara, 1979]. However, the discrepancies between these models in a description of the above indicated dependencies even in quiet solar and geomagnetic conditions of middle and lower latitudes are so strong that the question on the causes of the discrepancies is inevitable. As one of such causes, Danilov et al. [1991] considered meteorological effects of the winter anomaly (WA) and stratospheric warmings (SW). Both these phenomena influence strongly and in the opposite directions the structure of the midlatitude lower ionosphere in winter months. Another possible source of the systematic discrepancy between the above indicated models is the longitudinal effect. The role of this effect in formation of the global structure of the D region was considered only in the McNamara [1979] model. At the same time, the satellite measurements of nitric oxide in the lower thermosphere indicate to a relation of [NO] at a height of 105 km not only to the geographic latitude, but to the geomagnetic latitude as well [Gravens and Stewart, 1978]. Bearing in mind that NO is the main ionized agent (actually a source of the D -region formation) and that its content in this region evidently is determined by the vertical transport, one can assume that longitudinal effects should also exist in the latitude-longitude structure of the lower ionosphere. To confirm this statement, one can refer to the results of the measurements of the ionospheric radio wave absorption by the A1 method conducted at the stations of the global network in the periods of IGY (International Geophysical Year) and IQSY (International Quiet Sun Year) [Belkina, 1968; Bremer et al., 1980; Fligel', 1962; George, 1971; Ginzburg and Nesterova, 1974; Givishvili, 1976; Schwentek, 1976; Shirke and Henry, 1967]. One should bear in mind that the A1 method provides a rough enough representation of the ne vertical profile and characterizes mainly the integral content of electrons in the column from the bottom of the ionosphere to the reflection point of the sounding signals located (most often) in the E region. The difficulties of reconstruction of the ne vertical profile we are going to eliminate in the following way. Finding a dependence of ne on these or that geophysical conditions in the altitude range 65-95 km, to fit the obtained ne(h) profiles of the D region to the ne(h) profiles in the E layer, the spatial and time variations of the latter being studied with a high degree of accuracy and reliability. Using the obtained in such a way vertical profiles of ne and the data on the vertical distribution of the neutral atmosphere density (electron collision frequencies), values of the integral absorption L (in dB) at frequencies used for the measurements by the A1 method at this or that station are calculated. The choice of the ne(h) profile corresponding to the corresponding analyzed solar and geophysical conditions is performed by the method of minimization of the difference between the calculated and measured values of L.
[3] The aim of the first part of this paper is to specify the regularities in the spatial-time structure of the lower ionosphere in the latitude interval 66oN-59oS on the basis of the data obtained mainly in rocket measurements (R) and by the partial reflection method (PR).