Unstable and damped modes in coupled ocean mixed layer and cloud models

The ocean mixed layer and clouds are coupled by the fluxes of momentum, heat, and water mass at the. interface. The importance of the fluxes of momentum and heat is well recognized by both meteorologists and oceanographers. However, the water mass flux has been given considerable attention only in atmospheric models since the latent heat release is an important source of energy for the atmospheric general circulation. The water mass flux is given less attention in ocean models although it is realized that evaporation and precipitation contribute to the surface buoyancy flux which influences the depth of mixing and the thermohaline circulation. Clouds and the ocean mixed layer are coupled by both the heat and moisture fluxes across the air-ocean interface. Two time scales are demonstrated in this paper: a sea surface temperature (SST) evolution time scale, TT, that is virtually controlled by the oceanic planetary boundary layer (OPBL) and a cloud-SST coupling time scale tau(T) These two time scales depend on the stability of the marine atmospheric boundary layer (MABL). The more unstable the atmosphere, the shorter the time scales will be. For a stable atmosphere, tau(T)-1-3 years, and tau(n, T) - 0.3-1 years. However for an unstable atmosphere, tau(T) - 20-30 days, and tau(n,T) - 3-6 days. An air-ocean coupled model is presented in this paper for two different regimes: (1) the non-entraining ocean mixed layer case and (2) the entraining mixed layer case. The model results demonstrate that the exchanges of heat and water across the sea surface lead to both growing and decaying modes of oscillation on the two time scales due to the stability of the atmosphere. These oscillatory solutions are entirely thermodynamic and do not require wave dynamics for their existence.