A mixed-flux equilibrium asynchronous coupling scheme for accelerating convergence in ocean-atmosphere models

A coupled atmosphore/mixed-layer ocean energy balance model of intermediate complexity is used to examine the feasibility of a technique to accelerate the model's convergence rate while using equilibrium asynchronous coupling (EAC). EAC consists of an iterative sequence of integrations of an atmosph eric model driven to equilibrium with fixed SSTs, the output of which is us ed to drive an ocean model to equilibrium. In an attempt to accelerate a ra diatively perturbed climate to its final equilibrium state, we superimpose on the EAC scheme a mixed-flux condition, in which a portion of the turbule nt air-sea heat flux from the most recent atmospheric leg is used in the pr esent oceanic integration. In sensitivity tests using enhanced insolation, this mixed flux approach strongly hastens the model's convergence rate, who se acceleration is regionally dependent the tropics show the strongest sens itivity to the mixed-flux condition, while polar regions are least affected . This geographic variation stems from the presence of polar sea-ice, which promotes a temperature inversion and thereby causes a seasonal change in t he sign of the total turbulent air-sea heat flux. Potential applications an d limitations of this accelerated EAC method are also discussed.