On the Movement of Planetary Waves in Wavenumber-Period Space

[摘要] The movement of zonal harmonic waves with wavenumbers n=1-6 and with different periods is studied at the 500-mb level and 60°N in 20 winters since 1947/48. The deviations from various running means and the 24-hour tendency field are utilized, and on the basis of time-longitude harmonic analysis, which is essentially equivalent to quadrature spectrum analysis, the movement of travelling waves is investigated in the wavenumber-period space.It is shown that the planetary waves with n=1 and 2 and with periods from 10 to 50 or 60 days move generally westward, and that the wave n=2 with a period of 3 days, the wave n=3 with periods smaller than 10 days and waves n≥4 with periods smaller than 30 days, move mostly eastward. For n=3 retrogressive and progressive waves are observed in the range of periods from 10 to 30 days. Thus for periods larger than about 10 days the wave n=3 separates the travelling waves into retrogressive and progressive waves. The travelling wave n=6 with longer periods are considered to be non-existent because the amplitude of the wave is very small. For the remaining periods the existence of travelling waves is not known mainly owing to the lack of sufficient data. Accordingly the wavenumber-period space is composed of five domains and a schematic model of the travelling planetary-scale waves is presented. In general the amplitude of planetary waves increases with increasing period and decreasing wavenumber but it is almost independent of the period for the higher wavenumbers. As regards the amplitude the wavenumber-period space is divided into two domains, and the amplitude is nearly proportional to period and wavenumber in the first and second domains respectively.

[学科分类] 大气科学