SPECTRAL ENERGY CONTRIBUTIONS OF QUASI-PERIODIC OSCILLATIONS (2-35 DAYS) TO THE VARIABILITY OF THE F(0)F2

The relative contributions of quasi-periodic oscillations from 2 to 35 days to the variability of f(o)F2 at middle northern latitudes betwee n 42 degrees N and 60 degrees N are investigated. The f(o)F2 hourly da ta for the whole solar cycle 21 (1976-1986) for four European ionosphe ric stations Pome (41.9 degrees N, 12.5 degrees E), Poitiers (46.5 deg rees N, 0.3 degrees E), Kaliningrad (54.7 degrees N, 20.6 degrees E) a nd Uppsala (59.8 degrees N, 17.6 degrees E) are used for analysis. The relative contributions of different periodic bands due to planetary w ave activity and solar flux variations are evaluated by integrated per cent contributions of spectral energy for these bands. The observation s suggest that a clearly expressed seasonal variation of percent contr ibutions exists with maximum at summer solstice and minimum at winter solstice for all periodic bands. The contributions for summer increase when the latitude increases. The contributions are modulated by the s olar cycle and simultaneously influenced by the long-term geomagnetic activity variations. The greater percentage of spectral energy between 2 to 35 days is contributed by the periodic bands related to the midd le atmosphere planetary wave activity.