Transient non normal growth and optimal stochastic forcing of thermohaline variability

The non normal stability behavior of the thermohaline is studied using a simple box model. Physical Mechanisms are explored both for rapid transient amplification of the thermohaline circulation and for optimal stochastic forcing of thermohaline variability. It is found that in a stable parameter regime in which small perturbations eventually decay, there is the possibility for rapid (O(2-3) years) growth of THC anomalies due to the non normal nature of the model dynamics. The relevance of this transient amplification to the nonlinear switches between different steady states of the model is explored.