Summary: The study analyses how many harmonic component waves describe the meridional global profile of sea-level pressure distribution reliably; in addition, it analyses whether cycles or quasi-periodicities can be found on the Earth, in the temporal course of sea-level pressure. The real periodicities are determined by a statistical significance test. The yearly and half-yearly cycles are presented in vectorial form.

It has been established that the 1st and 2nd harmonics of the meridional global profile of air pressure distribution well reflect the uneven distribution of sea-level pressure between the two hemispheres. The 3rd harmonic, which shows the steady features of global air pressure field, is a factor of lesser importance. All the further harmonics are unimportant in the formation of this profile. The investigation of the yearly and half-yearly cycles of sea-level pressure has essentially led - on a different data basis - to the same conclusions to which Hann and Süring (1939), as well as Hsu and Wallace (1976) had come. On the basis of the statistical significance test of the periodical component waves obtained by a harmonic analysis of the sea-level pressure time series it can be found that on the Earth, in the temporal course of sea-level pressure, there exist only two kinds of cycles the characteristic 12-month and the less sharp 6-month one. Consequently, the great number of, and very different, periodicities pointed out in the temporal course of sea-level pressure and considered to be statistically significant by numerous authors, are probably not real ones. The most frequently investigated periodicities - the 11-year sunspot cycle, the tropospheric quasi-biennial (mostly 26-month) oscillation, and the Southern Oscillation - are not reflected in the temporal course of sea-level pressure.