THE INFLUENCE OF THE MEAN STATE ON INTERDECADAL VARIABILITY IN FLAT-BOTTOMED OCEAN MODELS

It has been well-demonstrated that many flat-bottomed ocean models pos sess interdecadal oscillatory solutions. Recently, propagation of visc ous (or coarsely resolved) Kelvin waves around the boundary has been i mplicated in the oscillations. In this paper, we examine how the mean state affects the character of the oscillation. We find that the strat ification along the northern boundary has a large effect upon the osci llation. Mean states with an essentially unstratified north-east corne r, lead to long period oscillations as the viscous boundary wave slowl y crosses the northern boundary. Conversely, mean states with a strati fied north-east corner, but unstratified north-west corner, lead to sh ort-period, but larger-amplitude, oscillations since boundary wave pro pagation is arrested only in the north-west corner. We demonstate that the different character of oscillations under different zonal redistr ibutions of a diagnosed flux are a consequence of the different mean s tates induced by the redistribution.