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Abstract: Tropical cyclone intensity is strongly affected by the air‐sea heat flux beneath the storm. When strong storm winds enhance upper ocean turbulent mixing and entrainment of colder water from below the thermocline, the resulting sea surface temperature cooling may reduce the heat flux to the storm and weaken the storm. Recent studies suggest that this upper ocean turbulence is strongly affected by different sea states (Langmuir turbulence), which are highly complex and variable in tropical cyclone conditions. In this study, the upper ocean response under Hurricane Edouard (2014) is investigated using a coupled ocean‐wave model with and without an explicit sea state dependent Langmuir turbulence parameterization. The results are compared with in situ observations of sea surface temperature and mixed layer depth from AXBTs, as well as satellite sea surface temperature observations. Overall, the model results of mixed layer deepening and sea surface temperature cooling under and behind the storm are consistent with observations. The model results show that the effects of sea state dependent Langmuir turbulence can be significant, particularly on the mixed layer depth evolution. Although available observations are not sufficient to confirm such effects, some observed trends suggest that the sea state dependent parameterization might be more accurate than the traditional (sea state independent) parameterization. [ABSTRACT FROM AUTHOR]

The evolution and propagation of large anticyclonic eddies similar to the Loop Current eddies found in the Gulf of Mexico are studied in a two-layer intermediate equation numerical model. It is found that the propagation of these eddies is governed primarily by the β effect, lower-layer flow driven by the surface eddies, and the image effect. As the eddies move westward under the influence of the β effect, they drive deep circulation that typically includes a cyclone near the eddies' trailing edge. This cyclone accelerates the eddy southward, leading to a path substantially different from that found in reduced-gravity models of similar surface eddies. When the eddy encounters a continental slope, the lower-layer flow is dispersed by topographic Rossby waves, and the eddy loses its southward propagation component. If the continental slope is backed by a shelf that is wider than the eddy's radius, a deep anticyclone will form over the shelf as the eddy approaches the shelf break. This anticyclone will drive the surface eddy rapidly southward until it crosses the shelf break and encounters the boundary, where the eddy will turn northward under the influence of the image effect. Eddies initialized over a zonal slope, which cannot develop the deep circulation that accelerates the eddy southward because of topographic Rossby wave dispersion, propagate nearly zonally until they encounter the western boundary. Over a northern slope such as that found in the Gulf of Mexico, these eddies will retroflect and propagate westward under the influence of the image effect if the northwest corner shelf is narrow, but they will turn southward along the western boundary if the northwest corner shelf is wide. [ABSTRACT FROM AUTHOR]

A mesh movement scheme is implemented in a multiply nested primitive equation ocean model. Mesh movement can be specified or determined in the course of the model run so as to follow an evolving oceanic feature, such as a wave front or propagating eddy, or atmospheric forcing, such as a tropical cyclone. Mass, heat, and momentum are conserved during the movement. The mesh movement scheme is tested in idealized and realistic configurations of the model. The idealized tests include simulations in which the moving meshes follow a propagating equatorial Kelvin wave, a dipole, or move across an existing mesoscale eddy. The tests demonstrate that the solutions in the fine-mesh region of the nested meshes reproduce well the equivalent solutions from uniform fine-mesh models. The model is applied for simulations of the ocean response to tropical cyclones, in which the moving meshes maintain high resolution near the cyclone center. The solution in the inner meshes reproduces very well the uniform fine-mesh simulation, in particular the sea surface temperature. It demonstrates that the moving meshes do not degrade the solution, even with the application of strong winds and the generation of energetic surface currents and near-inertial gravity waves. The mesh movement scheme is also successfully applied for a real-case simulation of the ocean response to Typhoon Roy (1988) in the western North Pacific. For this experiment, the model is initialized using the fields from a general circulation model (GCM) multiyear spinup integration of the large-scale circulation in the tropical Pacific Ocean. The nested-mesh solution shows no difficulty simulating the interaction of the storm-induced currents with the existing background circulation. [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC)-ocena feedbacks are studied using a coupled tropical cyclone-ocean model consisting of an eightlayer triply-nested movable grid model of a TC and a three-layer primitive equation ocean model. The numerical results indicate that the TC-ocean interaction influences intensities, structures, and the trajectories of tropical cyclones. Two possible mechanisms, barotropic and baroclinic, influencing TC tracks under TC-ocean interaction are suggested. The barotropic mechanism is related to the changes of the vertically averaged TC structure, induced by the TC-ocean coupling. The baroclinic mechanism is related to the asymmetry of the condensation heating within the TC caused by the asymmetry of heat and moisture fluxes at the sea surface. This asymmetry arises due to the asymmetry in sea surface cooling relative to the storm center. The experiments indicate that the influence of TC-ocean interaction on the TC tracks is the greatest for the case of a zero background flow. In the case of a non-zero background flow the sensitivity of storm tracks to the coupling with the ocean decreases. It is found that the influence of the ocean coupling on the TC track is quite sensitive to the method of convective heating parameterization in the TC model. The TC-ocean interaction also results in a change of the amount and spatial distribution of precipitation. [ABSTRACT FROM AUTHOR]

A new multiply nested primitive equation ocean model is presented. The model employs a two-way interactive nesting technique successfully applied for many years in the Geophysical Fluid Dynamics Laboratory--NOAA hurricane prediction model. The formulation of the mesh nesting algorithm allows flexibility in deciding the number of meshes and the ratio of grid resolutions between adjacent meshes. Other advanced features include realistic coastline geometry and spatially variable grid spacing. The results of various idealized experiments indicate good performance of the nesting technique. The most important feature of the model is the ability to combine large-scale and regional-scale predictions. The model is tested as a general circulation model (GCM) in a 3-yr spinup experiment of the large-scale circulation in the tropical Pacific Ocean. It demonstrates skill comparable to that of other recently developed GCMs. The resulting large-scale fields are then used in the nested configuration as initial conditions for simulations of the ocean response to a westerly wind burst and a tropical cyclone. Significant improvements over a coarse, single-mesh model have been achieved in resolving finescale features of the wind-induced current and temperature fields. These results highlight the importance of model resolution for realistic simulations of mesoscale ocean variability. [ABSTRACT FROM AUTHOR]