Discrete Spectra and Continuous Spectrum of the BarotropicQuasi-Geostrophic Model-A Calculation ofMeteorological Data

摘要

Atmospheric disturbances at 300 hPa are decomposed into normal modes, referred asdiscrete-spectrum disturbances which can propagate freely in the observed zonal mean flow, andnon-modal transient disturbances, referred as continuous-spectrum disturbances which arecontinuously sheared and eventually absorbed by the zonal flow. It is shown that normal modesrepresent only a small fraction of the observed atmospheric disturbances, while continuous-spectrum disturbances represent the majority of observed disturbances, even when the basic flow isunstable.Daily variabilities 0f the observed continuous-spectrum disturbances are presented. They areshown to follow the results of wave-packet theory. Calculations suggest that there are abundantsources to excite continuous-spectrum disturbances in the atmosphere.