A GLOBAL EMPIRICAL-MODEL OF EFFECTS OF LARGE-SCALE INTERNAL GRAVITY-WAVES IN THE NIGHTTIME IONOSPHERE

On the basis of an analysis of a large amount of data from the vertica l ionospheric sounding stations located in the Northern half of the Ea stern hemisphere, a global empirical model of variations of f(o)F2 and the F2 layer height associated with large-scale internal gravity wave s (IGW) during magnetospheric substorms and the first few hours of mag netic storms is constructed. The model is valid for night hours in the interval from subauroral latitudes to equatorial ones for all seasons and for different levels of solar activity. The model allows one to e stimate the probability, delay relative to substorm onset, amplitude a nd time evolution of the IGW effects in the ionospheric F region. Usin g this model, the main features of the IGW effect in the ionospheric F region are derived depending on season, latitude: and levels of solar and magnetic activities. It is found that the IGW probability is quit e high; it increases with increases of substorm intensity and solar ac tivity. For substorms with AE(max) > 1000 nT in years of solar maximum , this probability amounts to as much as 100%. The IGW amplitude also increases with increases of substorm intensity and solar activity. The IGW effect amplitude depends on solar activity nonlinearly: it increa ses appreciably when F-10,F-7 changes from 75 to 150 and almost does n ot vary when F-10,F-7 grows from 150 to 200. At high solar activity, s easonal variations are clearly exhibited: the IGW effect amplitude is noticeably greater in winter and the equinoxes than in summer. In year s of solar minimum, seasonal variations are negligible. For all season s and levels of solar and magnetic activities, the effect amplitude is greatest at subauroral latitudes and then decreases smoothly as the l atitude is reduced, with a local maximum near geomagnetic latitude phi = 20 degrees. Interpretations of some features of the effect are sugg ested. (C) 1998 Elsevier Science Ltd. All rights reserved.