Evolution of atmospheric baroclinic waves
The evolution of atmospheric baroclinic waves is investigated by a six-layer forced dissipative quasi-geostrophic $\beta$-plane channel model. In the control run, the model has: (i) a realistic zonal thermal forcing, (ii) a surface Ekman layer, a Newtonian cooling and an interior biharmonic friction as the dissipation and (iii) an initial state consisting of a weak but general wave field superimposed on a jet-like zonal mean flow. The whole evolution of the baroclinic waves can be divided into three periods; namely, the baroclinically growing period in which the synoptic waves grow exponentially, the transition period in which the synoptic waves decay and the planetary waves grow, and the equilibration period in which the planetary waves become dominant. The synoptic waves stop growing exponentially due to the wave-wave interaction as well as the barotropic decay as pointed out by Simmons and Hoskins (1978). The planetary waves are forced by the synoptic waves through the nonlinear cascade process. The energy spectra show a $\lambda\sp{-3}$ distribution in the region of high total wavenumber ($\lambda$) and a $\lambda\sp{-5/3}$ distribution in the low wavenumber region.
University of Illinois - Urbana-Champaign
Networked Digital Library of Theses and Dissertations
University of Illinois at Urbana-Champaign