The theory of non-linear oscillator applied to the BiOS mechanism

TL;DR

This paper models the BiOS mechanism in the Ionian Sea using a non-linear oscillator, specifically a Van der Pol equation, revealing decadal variability and stochastic resonance phenomena that explain observed circulation reversals.

Contribution

It introduces a dynamical systems model for BiOS, incorporating stochastic noise and periodic forcing, to explain long-term variability and resonance effects in sea circulation.

Findings

Decadal oscillations are captured by the Van der Pol model.

Periodic forcing induces period doubling in the system.

Stochastic resonance enhances long-term variability understanding.

Abstract

The observed pseudo-periodic 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 mechanism seems to be very well described by a non-linear oscillator dynamical system. By setting the state variables as the salinity of Adriatic deep water and the sea level anomaly in the Ionian region a Van der Pol equation has been obtained. The periodic cycle so obtained is of the order of a decade as observed in the data. Furthermore, a periodic term, which mimics the decadal variability of the forcing (mainly atmospheric), produces a period doubling phenomenon which is typical of the forced Van der Pol oscillator. By considering also a stochastic gaussian noise acting as a forcing and a decadal periodic input term, having an amplitude much smaller than the noise variance, a sub-harmonic stochastic resonance appears in the solution for a certain range of the values of the parameters. This yields the possibility of a longer time scale variability of the BiOS mechanism.