The peculiarities of the manifestation of long-time oscillations in variations of critical frequency of an ionosphere F2-layer

On a database of vertical sounding of the ionosphere, received on middle-latitude stations Irkutsk (52.5°N, 103°E), Moscow (55.5°N, 37.3°E), and Boulder (40.0°N, 254.7°E) we investigated features of display of the long-period fluctuations (with the periods of internal atmospheric planetary waves) in variations of critical frequency of a F2-layer for a maximum and a minimum of solar activity. Existence of fluctuations with the periods ∼7, -10, -16, -22 and -27 days has been revealed. Their amplitude and time of existence essentially depend on a level of solar activity, a season and regional features. It is shown, that in a minimum of solar activity fluctuations with the shorter periods ( 20 days) were more often observed. Fluctuations with the periods - 16 days are most on a regular basis shown, in the summer they can be present during two months. It is established, that fluctuations such as planetary waves in Eastern Siberia are observed approximately in 2 times more often, than in Northern America.