Abstract
Properties of the quasi-stationary Rossby waves along the westerly jets are investigated with the space-time spectral analysis of 200hPa meridional wind velocity for four regions in the Northern Hemisphere summer using ECMWF data for 1980 to 1993. The observed zonal wavenumber of eastward (westward) propagating disturbances increases (decreases) as the frequency increases. The eastward propagating disturbances are stronger than the westward propagating ones. The quasi-stationary Rossby waves are seen not only in 10- to 30-day time scales but also in 30- to 90-day time scales.
These observed zonal wavenumber-frequency relationships are reproduced by a β-channel model with step-like basic states. Calculated zonal wavenumber of eastward (westward) propagating solution of this model increases (decreases) as the frequency increases. The eastward propagating solutions are more strongly trapped in the westerly jet than the westward propagating ones. For these four waveguides mentioned, the results of the spectral analysis agree with the properties of the solutions deduced from the β-channel model with basic states derived from the climatological basic flow near these waveguides.
