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 possess interdecadal oscillatory solutions. Recently, propagation of viscous (or coarsely resolved) Kelvin waves around the boundary has been implicated in the oscillations. In this paper, we examine how the mean state affects the character of the oscillation. We find that the stratification along the northern boundary has a large effect upon the oscillation. Mean states with an essentially unstratified north-east corner, lead to long period oscillations as the viscous boundary wave slowly crosses the northern boundary. Conversely, mean states with a stratified north-east corner, but unstratified north-west corner, lead to short-period, but larger-amplitude, oscillations since boundary wave propagation is arrested only in the north-west corner.We demonstate that the different character of oscillations under different zonal redistributions of a diagnosed flux are a consequence of the different mean states induced by the redistribution.