Is the bimodal oscillating Adriatic-Ionian circulation a stochastic resonance?

The observed pseudoperiodic reversal of the upper-layer circulation of the Ionian Sea has been assumed to be related to some internal feedback processes (density driven) by the so-called BiOS (Adriatic-Ionian Bimodal Oscillating System) hypothesis. The idea behind this paper is that the Ionian circulation is driven by what happens in the boundary of the region, and so a very simple dynamical model has been derived by integrating in the bounded flow domain (the Ionian Basin) on the f-plane of the two-layer quasi-geostrophic evolution equations. Furthermore, a nonlinear term which mimics the mutual interaction between the moving layers has been introduced. By considering a stochastic Gaussian noise acting as a forcing and a decadal periodic input term having an amplitude much smaller than the noise variance, a stochastic resonance appears in the solution for a certain range of the values of the parameters. The decadal forcing at the boundary of the Ionian basin can be related to the low-frequency atmospheric variability in the surrounding basins. The resonance has a period consistent with the observed decadal time scale of the reversal between cyclonic and anti-cyclonic phases.