A recent advance in the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) is described and used to study two-way air-sea coupling and its impact on two different weather scenarios. The first case examines the impact of a hurricane-induced cold ocean wake on simulated changes in the structure of Hurricane Katrina. The second case investigates the effect of wind-and current-induced island wakes and their impact on the local electromagnetic (EM) and acoustic propagation characteristics in the Southern California Bight region. In the Katrina case, both the atmosphere and ocean show a strong response from airsea interaction. The model results show that wind-induced turbulent mixing, vertical advection, and horizontal advection are the three primary causes of the development of the trailing cold ocean wake. A distinct spatial separation is seen in these three primary forcing terms that are generating the bulk of the cooling in the ocean mixed layer. An asymmetric tropical cyclone structure change has been documented in detail from a more realistic, full physics, and tightly coupled model. These changes include a broadening of the eye, a reduced radius of hurricane-force wind, and a pronounced inner-core dry slot on the west side of the storm. In the island wake experiment, many finescale variations in the wind, current, and static stability structure resulting from the two-way interaction are described. These variations take the form of narrow vorticity and temperature anomalies that are found to reside in the ocean and atmosphere well downwind from the Channel Islands. Upwind differences in the lower-atmospheric wind and thermal structure also arise and are found to have a small impact on the lee-flow structure and EM characteristics of the southernmost Channel Islands.

In this paper the effect of a summer Mistral event on the Ligurian and Tyrrhenian Seas in the northwestern Mediterranean is discussed, using a coupled numerical model and satellite and in situ observations. The focus is on the spatial and temporal distribution of the ocean mixed layer response to the strong winds, and on how this is affected by atmosphere-ocean coupling. The model used is the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS Ò1), developed at the Naval Research Laboratory. This system includes an atmospheric sigma coordinate, non-hydrostatic model, coupled to a hydrostatic sigma-z level ocean model (Naval Coastal Ocean Model), using the Earth System Modeling Framework (ESMF). The model is run at high (km scale) resolution to capture the fine structure of wind jets and surface cooling. Two non-assimilating numerical experiments, coupled and uncoupled, are run for a 3-day period of a Mistral event, to examine more closely the impact of coupling on the surface flux and sea surface temperature (SST) fields. The cooling of SST up to 3°C over 72 h in the coupled run significantly reduced the surface momentum and heat fluxes, relative to the uncoupled simulation, where the SST was kept fixed at the initial value. Mixed layer depths increase by as much as 30 m during the event. A heat budget analysis for the ocean is carried out to further explain and investigate the SST evolution. Shear-induced mixing in inertial waves is found to be important to the surface cooling. Effects of coupling on the atmospheric boundary layer are found to be significant, but overall the effect of coupling on the synoptic low pressure system is small.

In situ experimental data and numerical model results are presented for the Ligurian Sea in the northwestern Mediterranean. The Ligurian Sea Air-Sea Interaction Experiment (LASIE07) and LIGURE2007 experiments took place in June 2007. The LASIE07 and LIGURE2007 data are used to validate the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) 1 developed at the Naval Research Laboratory. This system includes an atmospheric sigma coordinate, nonhydrostatic model, coupled to a hydrostatic sigma-z-level ocean model (Navy Coastal Ocean Model), using the Earth System Modeling Framework (ESMF).A month-long simulation, which includes data assimilation in the atmosphere and full coupling, is compared against an uncoupled run where analysis SST is used for computation of the bulk fluxes. This reveals that COAMPS has reasonable skill in predicting the wind stress and surface heat fluxes at LASIE07 mooring locations in shallow and deep water. At the LASIE07 coastal site (but not at the deep site) the validation shows that the coupled model has a much smaller bias in latent heat flux, because of improvements in the SST field relative to the uncoupled model. This in turn leads to large differences in upper-ocean temperature between the coupled model and an uncoupled ocean model run.

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