Temporal and spatial distribution of the spectral components of foF2

A spectral analysis of almost all available monthly median of the maximum plasmafrequency in the F-region (foF2) was performed. Some evidence for a significant tidal influence on the diurnal and semidiurnal variation has been found. The declination effect (Eyfrig, 1963) appears in our spectral presentation as a dependence of the degree of the seasonal variation and of the phase of the 24 hour period on the magnetic declination. The most peculiar phenomenon is the different variation of the annual component in North America and Eurasia with the sunspot number. There are several indications that the variation of (foF2) is also influenced by the variation of the gravitational potential. Some other results are presented which are believed to be related to dynamic processes in the F-region.