Abstract
Radio wave propagation measurements in the lower ionosphere over Europe allow us to deduce long-term trends in some parameters of the neutral upper middle atmosphere. The multi-frequency radio wave absorption measurements have been used to infer the planetary wave activity over the 1960s – early 1990s. The indirect phase reflection height measurements (IPHA) allow to follow relative variations of pressure near 80 km. The pattern of planetary wave activity provided by measurements along eight radio paths displays no trend in the 1960s and either positive or no (= statistically insignificant) trends in the 1970s and 1980s. IPHA data show a negative trend, i. e. decreasing pressure probably as a result of cooling. These trends are supposed to be of anthropogenic origin, but may also be caused by an unknown long-term (time scale of decades) natural variation.
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