Dynamical and thermal feedback mechanisms between the atmosphere and ocean surface

Two kinds of feedback mechanisms in the coupling process between the atmosphere and ocean surface are identified in this paper. One is a negative feedback mechanism, which is effective in the dynamic interaction process through momentum flux exchange between the atmosphere and ocean waves. In this mechanism, the ocean extracts momentum or wind stress from the atmosphere as a forcing field to generate ocean waves, which at the same time slows the atmospheric motion down, due to the loss of momentum by the friction effect. The second is a positive feedback mechanism, which is effective in the thermal interaction process through heat flux exchange. This positive feedback mechanism enhances the transport of sensible and latent heat fluxes to the atmosphere from the underlying ocean surface. As a result, the atmosphere obtains energy from the ocean, which intensifies the corresponding atmospheric motion, for example synoptic systems.

We also show that dynamic interactions can the dominate over thermal interactions, with respect to the coupled atmosphere - ocean system, due to the duration over which they are effective. Thermal interactions dominate only in favorable atmospheric-ocean conditions. The relation between thermal and dynamical interactions, and dominance of one over the other is shown to have implications for storm intensification, or weakening. We present a simple heuristic analysis of the manner in which the balance of these processes are indicators for storm intensification/weakening. This is verified by computations using a standard boundary layer model. Further verification is given in terms of the regional NCAR climate model (RegCM) coupled to the WAM ocean wave model. We present detailed computation, with comparisons to storm situations observed during the Labrador Sea Deep Convection Experiment (LSDCE) of 1997.