This work explores some aspects of the dynamics of baroclinic waves in a non-linearly equilibrated system. The analysis is numerical, using a two-layer quasigeostrophic model on a beta plane, relaxed to a zonally symmetric basic state with a radiative damping time scale. Such system is found to produce a statistically stationary climate, in which the baroclinic waves compete with the radiative forcing. The properties of the waves in the equilibrated system have been studied for different degrees of baroclinicity, and compared with their linear counterparts and the predictions of a linear stochastic model.
Except from a narrow band in the vicinity of the linear stability limit, for most values of the driving the spectrum at equilibration includes all waves. Consequently, as a difference with the more idealized non-linear initial value problem, non-linear wave-wave interactions are important at all stages of the development. The dynamics of the waves was found to be very different at low baroclinicity, when the extraction of energy from the mean is primarily quasi-linear, and at high criticality, when many waves are able to extract energy from the mean flow. In the latter case, the richness of the frequency spectrum of the non-linear forcing might explain the success of the linear stochastic model to reproduce the covariances of the full non-linear system.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics