Effects of non-Gaussian ocean-intrinsic variability in a stochastic Stommel two-box ocean model

The classical Stommel two-box ocean model is a minimal model of theocean thermohaline circulation. In certain parameter regimes of atmosphericforcing the model exhibits two stable equilibria, corresponding to a temperature-dominated regime and a salinity-dominated regime. Variability in theatmospheric forcing induces low frequency variability in the ocean circulation,and can induce transitions between the temperature-dominated and salinity-dominated regimes. Variability in the temperature and salinity (tracer)transport between boxes can also induce ocean-intrinsic variability andtransitions between regimes.We present a simple stochastic model for the fluctuations in the tracertransport between the boxes. The transport is modeled the product of acirculation anomaly and a tracer anomaly, where both anomalies are modeled asfast Gaussian stochastic processes. The resulting tracer transport exhibitsrapid, non-Gaussian fluctuations around a mean diffusive tracer transport.We examine the qualitative effects of this non-Gaussian stochastic inter-boxexchange, and compare to Gaussian models of inter-box exchange and to modelswith a deterministic exchange. All models include stochastic variability in theatmospheric forcing.