A simple atmosphere-ocean coupled model for the north Pacific interdecadal variability

A possible interdecadal oscillation mechanism in the North Pacific is investigated using a simple coupled ocean-atmosphere model, in which the surface wind stress is statistically modeled and the upper ocean dynamics is described by the Sverdrup balance. The SST anomaly depends upon the meridional heat transport by the Ekman and Sverdrup flow and the surface heat flux. The coupled model is the second-order delayed oscillator equation.

The ocean-atmosphere feedback in the North Pacific sufficiently induces the oscillatory mode in decadal time scale as mostly the weakly damped mode in the relevant parameter regime, so called 'Pacific Decadal Mode (PDM)'. The oscillation of PDM is accomplished by either the delayed dynamic adjustment due to the slowly propagating oceanic Rossby wave or the simultaneous thermodynamic adjustment induced by the switching back-and-forth between two leading SST-wind coupled modes having the monopole and the north-south dipole patterns. The meridional heat transport by the Sverdrup flow and Ekman flow plays a role in the oscillation and instability of PDM, respectively. The frequency and growth rate of PDM are mainly controlled by the time delay for consuming in the Sverdrup balance and the damping rate, respectively.