Abstract
Abstract. The relative contributions of quasi-periodic oscillations from 2 to 35 days to the variability of foF2 at middle northern latitudes between 42°N and 60°N are investigated. The foF2 hourly data for the whole solar cycle 21 (1976–1986) for four European ionospheric stations Rome (41.9°N, 12.5°E), Poitiers (46.5°N, 0.3°E), Kaliningrad (54.7°N, 20.6°E) and Uppsala (59.8°N, 17.6°E) are used for analysis. The relative contributions of different periodic bands due to planetary wave activity and solar flux variations are evaluated by integrated percent contributions of spectral energy for these bands. The observations suggest that a clearly expressed seasonal variation of percent contributions 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 solar 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 middle atmosphere planetary wave activity.Key words. Ionosphere · Ionosphere-atmosphere interactions · Mid-latitude ionosphere · Plasma waves and instabilities
Highlights
The existence and persistence of quasi-periodic oscillations with periods from 2 to 35 days, that play an important role in the variability of the ionospheric parameters, are found in many investigations
The relative contributions of dierent periodic bands due to planetary wave activity and solarux variations are evaluated by integrated percent contributions of spectral energy for these bands
The solar cycle and seasonal variations of the relative contributions of the main quasi-periodic oscillation bands from 2 to 35 days to the variability of foF2 is the purpose of the present study
Summary
The existence and persistence of quasi-periodic oscillations with periods from 2 to 35 days, that play an important role in the variability of the ionospheric parameters, are found in many investigations. The persistence of ten separate periodic bands, centred about a period of 2, 3, 5, 6.5, 9, 13.5, 18.6, 21.8, 27.4 and 31.5 days were found in the temporal variations of foF2 at northern middle latitudes during solar cycle 21 (Apostolov and Altadill, 1996) and the long-term variations (seasonal and solar cycle) of their oscillation characteristics were evaluated. These bands may be related with the analogous 2, 5, 10 and 16-day global middle atmosphere oscillations and with the direct solar ionization variations due to the solar rotation (27±29-days) and half solar rotation (13.5±14days) periods The amplitudes of these foF2 quasiperiodic oscillations are characterized by a considerable variability for dierent time scales, but with certain regularity in the temporal variations related to seasons and long-term solar and geomagnetic activity variations. Several potential mechanisms have been proposed to explain the inuence of the more intensively studied planetary 2-day wave in the middle atmosphere on the arising of upper ionosphere quasi-2-day oscillations. The solar cycle and seasonal variations of the relative contributions of the main quasi-periodic oscillation bands from 2 to 35 days to the variability of foF2 is the purpose of the present study
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