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. Longterm 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 degrees N, 105 degrees 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. (C) 2006 Elsevier Ltd. All rights reserved.