Evolution of large-scale variations of lower-thermospheric parameters over Irkutsk

For the first time, using many years of measurements of lower-thermospheric parameters (the horizontal wind velocity for 1976–1995, and minimum reflection frequency for 1983–1991) over Irkutsk (52°N, 105°E), the dynamics of their large-scale variations was investigated. The study used a sliding multiple correlation periodogram analysis. Regular seasonal, semi-annual and annual variations were detected. Quasi-biennial variations are regarded as irregular variations with a constantly changing over a rather wide range period. Variations with similar periods were also detected in the planetary index of geomagnetic activity A p, and in the solar radio flux index F 10.7. Our correlation analysis indicates that large-scale variations of the wind velocity and f min in the lower thermosphere are correlated with those in the geomagnetic field. The large-scale variations under investigation characterize a regular long-term variability of lower-thermospheric parameters and can serve as climatic characteristics for the description of the climate of this atmospheric region.