MODELING OF THE ELECTRON-DENSITY PROFILE IN THE LOWEST PART OF IONOSPHERE D-REGION ON THE BASIS OF RADIOWAVE ABSORPTION DATA .2. SEASONAL-VARIATIONS

A new model of the lowest part of the D-region is obtained by a trial- and-error inversion method. Its basic feature is a step-like transitio n between 55 and 70 km which is not depicted in most ionospheric model s. The seasonal differences of this are considered to be quite importa nt: the bottom of the ionsphere is found to be lower in summer and spr ing, the gradient of the profile below the CR-layer is stronger in win ter, and a well defined 'valley' exists around 70 km in spring. By sim ulating the ionospheric response to a solar flare (SID-effect) in summ er and in winter, an attempt was made to verify the obtained seasonal peculiarities of the quiet ionosphere. Copyright (C) 1996 Elsevier Sci ence Ltd