On the observed large-scale atmospheric wave motions

Abstract

On the basis of data from the whole Earth during different periods of the International Geophysical Year the large-scale wave motions at the 500 mb level, and to some extent the 1000 mb level, are studied. The waves are represented by spherical harmonic components of the height field for the whole Earth as well as for each of the two hemispheres. The relative importance of the different components in the expansion of the height field for the whole Earth is illustrared, and the seasonal variations at the two hemispheres are considered. The motion of the different wave components is investigated by computing mean values of the 24-hours phase angle changes. Except for the most large-scale, quasi-stationary components the mean velocities are found to be quite well in agreement with the Rossby-Haurwitz formula for the wave motions in a barotropic, non-divergent model with a solid rotating basic flow. The fluctuations of the quasi-stationary waves are studied by means of quadrature spectrum analysis and by application of different time filters. A certain part of the regular fluctuations seems to be attributed to various westward wave motions with different velocities of propagation. Each of these westward wave motions seems to be composed of more spherical harmonic components with different amplitudes. The quantitative results concerning the velocities of propagation and the amplitudes are generally supporting the idea that these wave motions may be explained essentially by the Rossby effect, for the most large-scale components combined with a divergence effect. DOI: 10.1111/j.2153-3490.1969.tb00427.x