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					   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, 917-946
                   Introduction

   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 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 outmost domain is stationary and ranged from 10oS
  to 65oN.
 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.
   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.
            Experimental design

   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 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.
                      Hurricane Gilbert

   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.
               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).
                      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.
                       Hurricane Opal

   The forecast
    starting at 0000
    UTC 2 Oct.
    produced a
    maximum
    cooling of 4.5o-
    4.7oC.
                 Hurricane Opal




   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.
   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).
                 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.
                   Hurricane Felix

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




   Cross section along 31.75oN
                    Hurricane Felix
   Sea-level pressure
                 Hurricane Fran
   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.
                    Hurricane Fran
   Cross section of SSTs
    along 31oN and 32oN
    from 3-day composite
    AVHRR satellite images
    and ocean model-
    predicted SSTs at the
    beginning of the coupled
    model forecast.
Hurricane Fran
1995-98 hurricane seasons
                      Summary

   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.

				
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posted:11/6/2011
language:English
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