Abstract
Regime behavior is investigated in a highly-truncated baroclinic spectral model with topography, frictional dissipation, and Newtonian cooling. Regimes are defined as the restriction of solution trajectories to isolated regions of phase space. "Trough regime" initiation is characterized by the retrogression of the largest scale wave into its preferred location upstream of the orographic ridge during periods of weak zonal winds. Prior to regime initiation, the wave typically amplifies, often due to topographic instability. Regime termination normally occurs as a synoptic-scale wave amplifies. Wave-wave interaction between the synoptic-scale and the large-scale wave is a requirement for regime termination; if this interaction is removed, regime transitions do not occur. Thus regime behavior, in this simple model, is understood in terms of pure Rossby wave dynamics, modified preferentially by ambient conditions. Large orographic scale waves entering the regime domain encounter weak westerlies permitting slow retrogression and weak baroclinicity, implying persistence much more frequently than would be expected by chance; no other features occur persistently with regime transition.
Kennedy, Laura Scott (1990). The initiation and termination of persistent atmospheric phenomena in a low order spectral model. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1108976.