Wj. Weng et Jd. Neelin, Analytical prototypes for ocean-atmosphere interaction at midlatitudes. Part II: Mechanisms for coupled gyre modes, J CLIMATE, 12(9), 1999, pp. 2757-2774
A simple midlatitude coupled model for idealized ocean basins is used to in
vestigate processes of ocean-atmosphere interaction and its role in interde
cadal climate variability at midlatitudes. The ocean model consists of a li
nearized quasigeostrophic upper ocean layer and a sea surface temperature (
SST) equation for an embedded surface mixed layer. The atmospheric response
to the ocean is through wind stress and heat flux feedbacks associated wit
h SST. Eigenvalue analysis of both coupled and uncoupled models presented h
ere complements previous work on the stochastically forced system. Comparis
on of the eigenspectrum of coupled and uncoupled cases shows that coupling
creates an oscillatory interdecadal mode whose properties are distinct from
any other mode in the system. This mode exists whether the atmospheric fee
dbacks are weak or strong, and is stable even in the strong feedback case.
The weak decay rate makes it possible fbr me mode to be maintained by atmos
pheric stochastic forcing. Analytic approximations to the dispersion relati
on show, how the spatial structure of the atmospheric feedback tends to sel
ect a large-scale spatial pattern for this eigenmode. The oscillation invol
ves westward Rossby wave propagation in the ocean with the atmosphere carry
ing information back eastward into the interior of the basin in response to
SST anomalies produced by advection. ST modes are also found, which purely
decay in most cases due to both local and nonlocal negative heat flux feed
backs. A case with large positive heat flux feedback can produce a purely g
rowing SST mode but does not greatly impact the interdecadal mode.