Amplification and Meridional Confinement of Stationary and Quasi-stationary Eddies in a Two-Layer Model

Roberto Benzi Dipartimento di Fisica, Università di Roma “Tor Vergata,” Rome, Italy

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Piero Malguzzi CNR-FISBAT, Bologna, Italy

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Abstract

The problem of resonance and meridional confinement of planetary-scale waves is investigated in the framework of a quasigeostrophic, two-layer, β-plane model with lateral sponge layers. It is shown that the model resonant wavenumber is meridionally confined despite the predictions of the linear barotropic theory based on the time-mean zonal wind. As a consequence, the fully nonlinear model exhibits a resonant response to orographic forcing significantly higher than that predicted by the linearized (baroclinic) version of the model itself.The model response to a localized (zonally and meridionally) orography is also studied and found to be consistent with previous results observed in spherical geometry. The significance of this result and the mechanisms leading to meridional confinement are discussed. It is suggested that nonlinearity and the inverse energy cascade process are responsible for the observed, enhanced wave confinement.

Abstract

The problem of resonance and meridional confinement of planetary-scale waves is investigated in the framework of a quasigeostrophic, two-layer, β-plane model with lateral sponge layers. It is shown that the model resonant wavenumber is meridionally confined despite the predictions of the linear barotropic theory based on the time-mean zonal wind. As a consequence, the fully nonlinear model exhibits a resonant response to orographic forcing significantly higher than that predicted by the linearized (baroclinic) version of the model itself.The model response to a localized (zonally and meridionally) orography is also studied and found to be consistent with previous results observed in spherical geometry. The significance of this result and the mechanisms leading to meridional confinement are discussed. It is suggested that nonlinearity and the inverse energy cascade process are responsible for the observed, enhanced wave confinement.

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