An AtmosphereOcean coupled model

1
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

2
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 .

3
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.

4
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.

5

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

6
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.

7
Experimental results

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

8
Hurricane Gilbert

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

9
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.

10
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).

11
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.

12
Hurricane Opal

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

13
Hurricane Opal

• Sea-level pressure
• In the experiments with both the coupling and the
  initial cold wake included, the storms intensity
  was much better reproduced compared to the
  operational forecast.

14

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

15
Hurricane Opal

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

16
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.

17
Hurricane Felix

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

18
Hurricane Felix
19
Hurricane Felix

• Cross section along 31.75oN

20
Hurricane Felix

• Sea-level pressure

21
Hurricane Fran

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

22
Hurricane Fran

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

23
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.

24
Hurricane Fran
25
1995-98 hurricane seasons
26
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.