Abstract
Planetary wave type oscillations have been observed in the lower and middle atmosphere but also in the iono- sphere, including the ionospheric F2 layer. Here we deal with the oscillations in foF2 analysed for two Japan- ese and two US stations over a solar cycle (1979-1989) with the use of the Morlet and Paul wavelet transforms. Waves with periods near 5, 10 and 16 days are studied. Only events of duration of three wave-cycles and more are considered. The results are compared with the results of a similar analysis made for foF2 and the lower ion- osphere over Europe (Lastovicka et al., 2003a,b). The 5-day period wave events display a typical duration of 4 cycles, while the 10- and 16-day wave events are less persistent with typical duration of about 3.5 cycles and rather 3 cycles, respectively, in all three geographic regions. The persistence pattern in terms of number of cy- cles and in terms of number of days is different. In terms of number of cycles, the typical persistence of oscilla- tions decreases with increasing period. On the other hand, in terms of number of days the typical persistence ev- idently increases with increasing period. The spectral distribution of event duration is too broad to allow for a reasonable prediction of event duration. Thus the predictability of the planetary wave type oscillations in foF2 seems to be very questionable. The longitudinal size of the planetary wave type events increases with increasing wave period. The persistence of the planetary wave type events in foF2 and the lower ionosphere is similar in Europe, but the similarity in occurrence of individual events in foF2 and the lower ionosphere is rather poor.
Highlights
Various processes in the lower-lying layers of the atmosphere, in the troposphere, summarized for simplicity under the term ‘meteorological processes’, can affect the ionosphere basically through two channels: i) electrical and electromagnetic phenomena, and ii) upward propagating waves in the neutral atmosphere
An example of the spectral distribution of event duration is shown in fig. 3, which presents for each region one station
The spectral distribution of event duration is too broad to allow a reasonable prediction of event duration from foF2 measurements themselves
Summary
Various processes in the lower-lying layers of the atmosphere, in the troposphere, summarized for simplicity under the term ‘meteorological processes’, can affect the ionosphere basically through two channels: i) electrical and electromagnetic phenomena, and ii) upward propagating waves in the neutral atmosphere. We treat the latter category, with upward propagating. Upward propagating waves in the neutral atmosphere and their modifications, interactions and modulations affect the ionosphere, when and if they reach it Those waves are planetary waves, tidal waves, gravity waves, and infrasonic waves.
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