A Note on the Spectral Density of Vorticity of Ultra-Long Waves in Middle Latitudes at the 500-mb Level in the Winter Season

[摘要] By making use of height data at the 500-mb level during a winter season (December 1974, January 1975, February 1975), the spectral densities of vorticities for ultra-long waves in the frequency domain are examined. The result shows that the spectral densities for zonal wavenumber k=1-3 are approximately proportional to the minus second power of the frequency in middle latitudes. The spectral densities for each term in the vorticity equation of ultra-long waves, such as the advection term and so-called β term, are also examined. And it is shown that the nonlinear interaction of baroclinic waves due to the advection term in the vorticity equation plays an important role in determining the rate of change of vorticity for ultra-long waves.In the last part of this paper, the statistical forecast of the height for ultra-long waves at the 500-mb level is discussed under the assumption that the height is regarded as a stationary random process. And it is noted that the mean square of forecast error tends to the climate variance in a few days.

[学科分类] 大气科学