LONG-TERM TRENDS IN PLANETARY WAVE ACTIVITY (2-15 DAYS) AT 80-100 KM INFERRED FROM RADIO-WAVE ABSORPTION

The daytime radio wave absorption in the lower ionosphere measured by the A3 method (oblique incidence on the ionosphere) in central and southeastern Europe is used to study long-term trends in the planetary wave activity in the period range of 2 15 days in the upper middle atmosphere. In central Europe we have found no trends in the 1960s and 1980s, but a positive trend in the 1970s (early 1970s-early 1980s); in southeastern Europe we have not established any trend in the 1970s, but a positive one in the 1980s (beginning in late 1970s). These trends are of non-solar origin. They are possibly an indication of changes of anthropogenic origin in the Earth's atmosphere.