A dynamical model of "quasi-stationary' states in large-scale atmospheric motions

Abstract

A theoretical study is made to establish the concept of "quasi-stationary (QS)' states in irregular, large-scale atmospheric motions by using a simple model. It is a truncated, two-layer, quasi-geostrophic model in a β-channel with surface topography, external thermal forcing (ie, meridional differential heating) and dissipative processes. We define a QS state as a period when the magnitude of the time derivative of spectral components, |x(t)|, is smaller than a prescribed threshold value. For a wide range of parameter values of the thermal forcing, each QS state is found to occur when the trajectory x(t) passes immediately next to a local minimum point (MP) of |x| in phase space; the MP is either a stationary solution or a nonstationary minimum point bifurcating from a limit point of a stationary solution. -from Author