An Atmosphere-Ocean coupled model Morris, A., Bender and Isaac Ginis, 2000 : Real-case simulations of hurricane-ocean interaction using a high-resolution coupled model: Effects on hurricane intensity. Mon. Wea. Rev., 128,

Introduction In order to study the effect of tropical cyclone-ocean interaction on the intensity of observed hurricanes. In order to study the effect of tropical cyclone-ocean interaction on the intensity of observed hurricanes. The GFDL movable triply nested mesh hurricane model was coupled with a high-resolution version of the Princeton Ocean Model (POM, Blumberg and Mellor, 1987). The GFDL movable triply nested mesh hurricane model was coupled with a high-resolution version of the Princeton Ocean Model (POM, Blumberg and Mellor, 1987). The ocean model had 1/6° uniform resolution, which matched the horizontal resolution of the hurricane model in its innermost grid. The ocean model had 1/6° uniform resolution, which matched the horizontal resolution of the hurricane model in its innermost grid.

Experimental design The grid system for each of the triply nested meshes in the present study is summarized in Table 1. The grid system for each of the triply nested meshes in the present study is summarized in Table 1. The outmost domain is stationary and ranged from 10 o S to 65 o N. The outmost domain is stationary and ranged from 10 o S to 65 o N. The two inner meshes are movable and follow the storm center. The two inner meshes are movable and follow the storm center.

Experimental design The POM is a three-dimensional, primitive equation model with complete thermohaline dynamics. The POM is a three-dimensional, primitive equation model with complete thermohaline dynamics. It has an ocean-bottom-following, sigma vertical coordinate system and a free surface. It has an ocean-bottom-following, sigma vertical coordinate system and a free surface.

The no. of vertical layers was set 21 and 23 which enabled the upper ocean dynamics to be represented with greater accuracy. The no. of vertical layers was set 21 and 23 which enabled the upper ocean dynamics to be represented with greater accuracy.

Experimental design The wind stress, heat, moisture, and radiative fluxes computed in the tropical cyclone model were passed into the ocean model. The wind stress, heat, moisture, and radiative fluxes computed in the tropical cyclone model were passed into the ocean model. The ocean model was then integrated one step and a new SST was calculated. The ocean model was then integrated one step and a new SST was calculated. The new SST was used in the ensuing time steps of the tropical cyclone model. The new SST was used in the ensuing time steps of the tropical cyclone model.

Experimental results The resulting prestorm SSTs and surface currents in the ocean model are shown in Fig. 2. The resulting prestorm SSTs and surface currents in the ocean model are shown in Fig. 2.

Hurricane Gilbert The track forecast made by the model was exceptio- nally accurate. The track forecast made by the model was exceptio- nally accurate.

Hurricane Gilbert Fig. 4 shows the comparison of the simulated SST and objectively analyzed observed fields from Shay et al. (1998) along the section AB in Fig. 3. Fig. 4 shows the comparison of the simulated SST and objectively analyzed observed fields from Shay et al. (1998) along the section AB in Fig. 3.

Hurricane Gilbert Time series of minimum sea level pressure for the operational forecast (solid line) and coupled experiment (dotted-dashed line) compared to observed values (thin dotted line). Time series of minimum sea level pressure for the operational forecast (solid line) and coupled experiment (dotted-dashed line) compared to observed values (thin dotted line).

Hurricane Opal The 72-h storm tracks (thin line) for two forecast of Hurricane Opal made by the coupled model starting at different initial time. The 72-h storm tracks (thin line) for two forecast of Hurricane Opal made by the coupled model starting at different initial time.

Hurricane Opal The forecast starting at 0000 UTC 2 Oct. produced a maximum cooling of 4.5 o o C. The forecast starting at 0000 UTC 2 Oct. produced a maximum cooling of 4.5 o o C.

Hurricane Opal Sea-level pressure Sea-level pressure In the experiments with both the coupling and the initial cold wake included, the storm ’ s intensity was much better reproduced compared to the operational forecast. In the experiments with both the coupling and the initial cold wake included, the storm ’ s intensity was much better reproduced compared to the operational forecast.

Fig. 9 indicates the dramatic effect the cold wake had on the accumulated evaporation throughout the period up to landfall. Fig. 9 indicates the dramatic effect the cold wake had on the accumulated evaporation throughout the period up to landfall.

Hurricane Opal The ratio for experiments was in fairly good agreement with the estimates of Emanuel (1986). The ratio for experiments was in fairly good agreement with the estimates of Emanuel (1986).

Hurricane Opal This suggest that the relationship obtained in these experiments between the storm intensity and the changes in the SST from the ocean-atmospheric interaction were reasonable. This suggest that the relationship obtained in these experiments between the storm intensity and the changes in the SST from the ocean-atmospheric interaction were reasonable.

Hurricane Felix The experimental case of Hurricane Felix in the western atlantic. The experimental case of Hurricane Felix in the western atlantic.

Hurricane Felix

Cross section along o N Cross section along o N

Hurricane Felix Sea-level pressure Sea-level pressure

Hurricane Fran The experimental case of Hurricane Fran in the western atlantic. The experimental case of Hurricane Fran in the western atlantic.

Hurricane Fran The SST distribution at 72-h for the two coupled experiments for Hurricane Fran run with and without Edouard ’ s wake. The SST distribution at 72-h for the two coupled experiments for Hurricane Fran run with and without Edouard ’ s wake.

Hurricane Fran Cross section of SSTs along 31 o N and 32 o N from 3-day composite AVHRR satellite images and ocean model- predicted SSTs at the beginning of the coupled model forecast. Cross section of SSTs along 31 o N and 32 o N from 3-day composite AVHRR satellite images and ocean model- predicted SSTs at the beginning of the coupled model forecast.

Hurricane Fran

hurricane seasons

Summary The effect of ocean coupling is one of the important mechanisms that govern the intensity of tropical cyclones. The effect of ocean coupling is one of the important mechanisms that govern the intensity of tropical cyclones. With inclusion of both the cold wake and the ocean coupling the intensity predictions is much improved. With inclusion of both the cold wake and the ocean coupling the intensity predictions is much improved.