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Hurricane Opal (1995) experienced a rapid, unexpected intensification in the Gulf of Mexico that coincided with its encounter with a warm core ring (WCR). The relative positions of Opal and the WCR and the timing of the intensification indicate strong air-sea interactions between the tropical cyclone and the ocean. To study the mutual response of Opal and the Gulf of Mexico, a coupled model is used consisting of a nonhydrostatic atmospheric component of the Naval Research Laboratory's Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS), and the hydrostatic Geophysical Fluid Dynamics Laboratory's Modular Ocean Model version 2 (MOM 2).The coupling between the ocean and the atmosphere components of the model are accomplished by conservation of heat, salt, momentum, as well as the sensible and latent heat fluxes at the air-sea interface. The atmospheric model has two nests with spatial resolutions of 0.6Њ and 0.2Њ. The ocean model has a uniform resolution of 0.2Њ. The oceanic model domain covers the Gulf of Mexico basin and coincides with a fine-mesh atmospheric domain of the COAMPS. The initial condition for the atmospheric component of COAMPS is the archived Navy Operational Global Atmospheric Prediction System operational global analysis, enhanced with observations. The initial ocean condition for the oceanic component is obtained from a 2-yr MOM 2 simulation with climatological forcing and fixed mass inflow into the Gulf. The initial state in the Gulf of Mexico consists of a realistic Loop Current and a shed WCR.The 72-h simulation of the coupled system starting from 1200 UTC 2 October 1995 reproduces the observed storm intensity with a minimum sea level pressure (MSLP) of 918 hPa, occurring at 1800 UTC 4 October, a 6-h delay compared to the observation. The rapid intensification to the maximum intensity and the subsequent weakening are not as dramatic as the observed. The simulated track is located slightly to the east of the observed track, placing it directly over the simulated WCR, where the sea surface temperature (SST) cooling is approximately 0.5ЊC, consistent with buoy measurements acquired within the WCR. This cooling is significantly less over the WCR than over the common Gulf water due to the deeper and warmer layers in the WCR. Windinduced currents of 150 cm s Ϫ1 are similar to those in earlier idealized simulations, and the forced current field in Opal's wake is characterized by near-inertial oscillations superimposed on the anticyclonic circulation around the WCR.Several numerical experiments are conducted to isolate the effects of the WCR and the ocean-atmosphere coupling. The major findings of these numerical experiments are summarized as follows. 1) Opal intensifies an additional 17 hPa between the times when Opal's center enters and exits the outer edge of the WCR. Without the WCR, Opal only intensifies another 7 hPa in the same period. 2) The maximum surface sensible and latent heat flux amounts to 2842 W m Ϫ2 . This occurs when Opal's surface circulation brings northwesterly...

Realistic simulations of the Adriatic Sea for over 125 days are conducted using the Navy Coastal Ocean Model with atmospheric forcing provided by the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS is a registered trademark of the Naval Research Laboratory (COAMPS™)). In two separate simulations of the Adriatic, a nested 2‐km‐resolution ocean model is forced by the inner (4‐km) and outer (36‐km) nests of the atmospheric model. Two meteorological stations and two acoustic Doppler current profiler observation sites are used to evaluate modeled atmosphere and ocean velocity fields for 28 January–4 June 2001. Modeled/observed correlations of atmospheric 10‐m velocity are greater than 0.85 for both resolution models. Oceanic 5‐ and 25‐m current fluctuations from both simulations generally match the magnitude and orientation of the observations. The 4‐km‐resolution atmospheric model is differentiated from the 36‐km‐resolution model by its ability to resolve the small‐scale flow structures of the “bora” wind and by its better agreement with observed wind velocity statistics. The ocean simulation forced by the 4‐km‐resolution model is distinguished from the one forced by the 36‐km‐resolution model by its ability to reproduce the expected double‐gyre circulation in the northern Adriatic and by its ability to better capture the magnitude and shape of the observed depth‐dependent velocity correlation with wind at the deeper site. Though the 36‐km forced ocean model agrees better with many observed velocity statistics, the 4‐km forced ocean model produces the highest correlations with observations (exceeding 0.78) at subsurface depths that are most strongly correlated with winds.

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.

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