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NASA NTRS1991

Nonlinear baroclinic adjustment

The concept of baroclinic adjustment is reexamined in the context of a fully nonlinear two-layer model on a beta-plane. Based on the results, a single, conceptually very simple mechanism of the nonlinear equilibration of waves and the mean flow is proposed, which is termed 'nonlinear baroclinic adjustment'. The new concept appears applicable to cases that currently require different explanations, varying from case to case, to account for the equilibration of the mean temperature gradient in the presence of external driving.

Cehelsky, Priscilla↗

NASA NTRS1987

Theories of multiple equilibria and weather regimes : A critical reexamination. II - Baroclinic two-layer models

Previous results based on low- and intermediate-order truncations of the two-layer model suggest the existence of multiple equilibria and/or multiple weather regimes for the extratropical large-scale flow. The importance of the transient waves in the synoptic scales in organizing the large-scale flow and in the maintenance of weather regimes was emphasized. The result shows that multiple equilibria/weather regimes that are present in lower-order models examined disappear when a sufficient number of modes are kept in the spectral expansion of the solution to the governing partial differential equations. Much of the chaotic behavior of the large-scale flow that is present in intermediate-order models is now found to be spurious. Physical reasons for the drastic modification are offered. A peculiarity in the formulation of most existing two-layer models is noted that also tends to exaggerate the importance of baroclinic processes and increase the degree of unpredictability of the large-scale flow.

Cehelsky, Priscilla↗