Statistical Characteristics of the Atmospheric Disturbances

Abstract

The periods of the atmospheric phenomena are supposed to differ from each other according to their scales, e. g., there may be a positive correlation between the magnitude of scales and length of periods in the atmosphere.
The purpose of this paper is to investigate the statistical characteristics of the atmospheric disturbances of various scales and further to find out the mechanism of mutual transfer of vorticity and kinetic energy of mean flow and disturbances. If we succeed in this attempt, the results obtained from are expected to be useful also for such a forecasting problem as numerical prediction. In the present study the following characteristics of the atmospheric phenomena are dealt with, that is, (1) the so-called “width of perturbations ”, (2) the stationarity of variations, (3) the spectral distribution of pressure and (4) the kinetic energy spectra, employing the 36 term harmonic coefficients calculated from the values of 500 mb level along 50°N, 45°N and 30°N latitude circles in the Historical Weather Maps. The periods subjected to analysis are January (1946,1949), May, June and July (1951).
The results obtained are as follows. First the component waves of disturbances can be classified into three (or four) parts. Then let n and F(n) denote wave number and spectral function respectively. The motion of waves of small wave number is non-isotropic, oscillatory and moreover F(n)=const. Meanwhile the motion of waves of great wave number is isotropic, progressive and F(n) ∝ n^-7/3 as expected. Further it may be concluded that the mean flow and the component waves of n=1,2 belong to the former and component waves of n=≤6 belong to the latter region. Accordingly the components of n=3, 4, 5 are considered to constitute the region of middle wave number in our case.
Next, the energy spectra indicate three sources of kinetic energy in the atmosphere, i. e., mean flow, component wave of n=3 and of n=6 or 7.