Trends in the characteristics of the annual and semiannual variations observed in the radio wave absorption in the lower ionosphere |
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| Authors: | J Lastovi?ka D Pancheva |
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| Institution: | (1) Institute of Atmospheric Physics, Academy of Science of the Czech Republic, Bocni II, CZ-14131 Prague 4, Czech Republic;(2) Department of Physics, University of Wales, Aberystwyth, Ceredigion, SY23 3BZ, UK;(3) Geophysical Institute, Bulgarian Academy Science, Acad. G. Bonchev str. bl. 3, BG-1113 Sofia, Bulgaria |
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| Abstract: | The continuous increase in concentration of greenhouse gases in the atmosphere is expected to cool higher levels of the atmosphere. There is some direct and indirect experimental evidence of long-term trends in temperature and other parameters in the mesosphere and lower thermosphere (MLT). Here we look for long-term trends in the annual and semiannual variations of the radio wave absorption in the lower ionosphere, which corresponds to the MLT region heights. Data from central and southeastern Europe are used. A consistent tendency to a positive trend in the amplitude of the semiannual wave appears to be observed. The reality of a similar tendency in the amplitude of the annual wave is questionable in the sense that the trend in the amplitude of the annual wave is probably induced by the trend in the yearly average values of absorption. The phases of both the annual and semiannual waves display a forward tendency, i.e. shift to an earlier time in the year. A tentative interpretation of these results in terms of changes of the seasonal variation of temperature and wind at MLT heights does not contradict the trends observed in those parameters. |
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| Keywords: | Ionosphere (ionosphere - atmosphere interactions mid-latitude ionosphere) Meteorology and atmospheric dynamics (middle atmosphere dynamics) |
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