Long-term variations of ionospheric parameters as a basis for the study of the upper-atmospheric climate

The challenge of climate is treated as a problem not only of statistical dynamics of the ground-level atmosphere but also of electrodynamics, with due regard for all atmospheric regions—from the troposphere to the boundary with the Earth’s magnetosphere. Long-term series of uniform measurements of the parameters of the thermosphere/ionosphere system make possible suggesting some climatic characteristics for the upper atmosphere. We present the results derived from analyzing the data of vertical-incidence ionospheric radio sounding (1948–1996) and the horizontal wind velocity measurements in the lower thermosphere/ionosphere (1976–1996) from observatory Irkutsk, East Siberia (52°N, 105°E). The analysis revealed long-term variations of such parameters as the minimum reflection frequency (fmin), the F-region virtual height (h ′F), the critical frequency (foF2), the electron density dispersion ( N) (spread-F parameter), the occurrence frequency of different types of sporadic ionospheric features, the virtual height of these sporadic layers, and the prevailing wind velocity in the height range 80–100 km. The association of climatic characteristics of the upper atmosphere with solar and geomagnetic activity, and the evolution of large-scale variations of the parameters under investigation are discussed.