An Atmosphere-An Atmosphere-Ocean coupled modelOcean coupled model

Morris, A., Bender and Isaac Ginis, 2000 : Real-case simulations oMorris, A., Bender and Isaac Ginis, 2000 : Real-case simulations of hurricane-ocean interaction using a high-resolution coupled mf hurricane-ocean interaction using a high-resolution coupled model: Effects on hurricane intensity. odel: Effects on hurricane intensity. Mon. Wea. Rev.Mon. Wea. Rev., , 128128, 917-94, 917-94

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IntroductionIntroduction

In order to study the effect of tropical cyclone-ocean iIn order to study the effect of tropical cyclone-ocean interaction on the intensity of observed hurricanes. nteraction on the intensity of observed hurricanes.

The GFDL movable triply nested mesh hurricane modThe GFDL movable triply nested mesh hurricane model was coupled with a high-resolution version of the Prel was coupled with a high-resolution version of the Princeton Ocean Model (POM, Blumberg and Mellor, 198inceton Ocean Model (POM, Blumberg and Mellor, 1987). 7).

The ocean model had 1/6° uniform resolution, which The ocean model had 1/6° uniform resolution, which matched the horizontal resolution of the hurricane mmatched the horizontal resolution of the hurricane model in its innermost grid .odel in its innermost grid .

Experimental designExperimental design The grid system for each of the triply nested The grid system for each of the triply nested

meshes in the present study is summarized in meshes in the present study is summarized in Table 1.Table 1.

The outmost domain is stationary and ranged The outmost domain is stationary and ranged from 10from 10ooS to 65S to 65ooN.N.

The two inner meshes are movable and follow the The two inner meshes are movable and follow the storm center.storm center.

Experimental designExperimental design

The POM is a three-dimensional, primitive equation mThe POM is a three-dimensional, primitive equation model with complete thermohaline dynamics.odel with complete thermohaline dynamics.

It has an ocean-bottom-following, sigma vertical coorIt has an ocean-bottom-following, sigma vertical coordinate system and a free surface.dinate system and a free surface.

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

Experimental designExperimental design

The wind stress, heat, moisture, and radiative fluxes cThe wind stress, heat, moisture, and radiative fluxes computed in the tropical cyclone model were passed inomputed in the tropical cyclone model were passed into the ocean model.to the ocean model.

The ocean model was then integrated one step and a The ocean model was then integrated one step and a new SST was calculated.new SST was calculated.

The new SST was used in the ensuing time steps of the The new SST was used in the ensuing time steps of the tropical cyclone model.tropical cyclone model.

Experimental resultsExperimental results

The resulting The resulting prestorm SSTprestorm SSTs and surface s and surface currents in thcurrents in the ocean mode ocean model are shown iel are shown in Fig. 2.n Fig. 2.

Hurricane GilbertHurricane Gilbert

The track foreThe track forecast made by tcast made by the model was he model was exceptio-nally exceptio-nally accurate.accurate.

Hurricane GilbertHurricane Gilbert

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

Hurricane GilbertHurricane Gilbert

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

Hurricane OpalHurricane Opal

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

Hurricane OpalHurricane Opal

The forecast The forecast starting at starting at 0000 UTC 2 0000 UTC 2 Oct. produced Oct. produced a maximum a maximum cooling of cooling of 4.54.5oo-4.7-4.7ooC.C.

Hurricane OpalHurricane Opal

Sea-level pressureSea-level pressure In the experiments with both the coupling and the initial cold wake In the experiments with both the coupling and the initial cold wake

included, the storm’s intensity was much better reproduced compared included, the storm’s intensity was much better reproduced compared to the operational forecast.to the operational forecast.

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

Hurricane OpalHurricane Opal

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

Hurricane OpalHurricane Opal

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

Hurricane FelixHurricane Felix

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

Hurricane FelixHurricane Felix

Hurricane FelixHurricane Felix

Cross section along 31.75Cross section along 31.75ooNN

Hurricane FelixHurricane Felix Sea-level pressureSea-level pressure

Hurricane FranHurricane Fran

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

Hurricane FranHurricane Fran

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

Hurricane FranHurricane Fran

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

Hurricane FranHurricane Fran

1995-98 hurricane seasons1995-98 hurricane seasons

SummarySummary

The effect of ocean coupling is one of the The effect of ocean coupling is one of the important mechanisms that govern the intensity important mechanisms that govern the intensity of tropical cyclones.of tropical cyclones.

With inclusion of both the cold wake and the With inclusion of both the cold wake and the ocean coupling the intensity predictions is much ocean coupling the intensity predictions is much improved.improved.