A Study of the Long Atmospheric Waves on the Basis of Zonal Harmonic Analysis

Characteristic features of the long atmospheric waves at middle latitudes are discussed on the basis of zonal harmonic analyses of hemispherical weather charts. In the first section mean values of the amplitudes of the waves with wavenumbers from 1 to 10 are presented for the 500-mb and the 1000-mb levels. Spectral distributions of the kinetic energy for the eastward and the northward components of the geostrophic wind at the 500-mb level are computed. In section 2 the semi-permanence of the waves with wavenumbers from 1 to 4 is illustrated. The meridional variation of the waves is investigated in relation to the question about the meridional transport of momentum. On the basis of the vertical variations of the waves of the January and July normal charts the causes of the semi-permanent waves are discussed. The traelling waves with wavenumbers 5, 6, and 7 are treated in section 3. Mean speeds of the waves are considered in relation to the mean velocity of the zonal flow. The vertical structure of the waves is investigated by means of the heights of the 1000-mb and 500-mb levels and the temperature field at the 500-mb level. Finally the speed and vertical structure of the waves are determined theoretically from the solutions of the linear equations in a two-level approximation.