Stability of zonal regimes in a truncated model of forced atmospheric flow

Summary The stability properties of zonal circulations induced by external forcing in a rotating atmosphere are investigated making use of a truncated model of the barotropic vorticity equation for forced, dissipative non-divergent flow in spherical geometry. Sufficient conditions for global and local asymptotic stability are found as a function of the dissipation time-scale, the coefficients of non-linear interaction between zonal flow and wave components, and the absolute rotation speed of the atmosphere. For weak, axisymmetric forcing fields the corresponding forced zonal circulation is a global attractor for states belonging to the configuration space of the model, while for larger forcing intensities it is only locally attracting, the extension of the basin of attraction being an increasing function of the absolute angular velocity of the atmosphere.

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Sommario Si analizzano le proprietà di stabilità di circolazioni zonali forzate in una atmosfera rotante facendo uso di un modello troncato a pochi modi dell'equazione di vorticità barotropica per flussi dissipativi in geometria sferica. Si determinano condizioni sufficienti per la stabilità asintotica sia locale che globale in funzione delle scale di tempo dissipative e di interazione nonlineare.

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This research was partly supported by C.N.R. through G.N.F.M.