CHARACTERISTICS OF QUASI-2-DAY OSCILLATIONS IN THE F(0)F2 AT NORTHERNMIDDLE LATITUDES

The temporal variations of the characteristics of f(o)F2 quasi-2-day o scillations at middle latitudes in the northern hemisphere are investi gated. The hourly data for the period 1976-1986 for four European iono spheric stations, Kiev (50.5 degrees N, 30.5 degrees E), Kaliningrad ( 54.7 degrees N, 20.62 degrees E), Lannion (48.75 degrees N, 3.45 degre es W) and Slough (51.48 degrees N, 0.57 degrees W), are used for analy sis. Periodogram and complex demodulation analysis are used to evaluat e the period and amplitude time variations of this oscillation. It is found that quasi-2-day oscillations in f(o)F2 are present almost conti nuously during the year. The amplitude is larger in the equinoxes and lower in the solstices. The amplitude variations are modulated by the long-term geomagnetic variations during the solar cycle. There is a cl ear expressed seasonal variation of the oscillation period with minimu m in the winter, November-February (42-47 hours), and maximum near sum mer solstice (48-55 hours). The observations suggest that there are th ree types of f(o)F2 quasi-2-day oscillations with behavior of (1) west ward traveling planetary wave with zonal wave number one, predominantl y during summer half year, with greatest occurrence in August, (2) sta tionary planetary wave with a maximum occurrence in the summer solstic e with unknown wave number, and (3) independent oscillations in separa te locations on relatively long distances. The vertical plasma drift v ariations can explain the annual and long-term modulation effects of f (o)F2 quasi-2-day amplitude variations but encounter significant diffi culties in explaining the discrepancy between zonal wave numbers in th e mesosphere (three) and upper ionosphere (one). Another possibility i s that the arising of quasi-2-day oscillation in the upper ionosphere may be induced by the forcing of such oscillation in the mesosphere wi th further independent development in the F region.