Technical Approach
The major tools of this project are high-resolution ocean and tropical
cyclone models used in either coupled or uncoupled configurations
(
Hurricane-Ocean Prediction System )
The first ocean model is the sigma-coordinate primitive equation
Princeton Ocean Model (POM). We have used the POM for the Atlantic
region and we plan to continue to use it for this area for the near
future. The POM is a three-dimensional, free-surface primitive
equation model. This model is widely distributed to the academic
community and used by the Navy in various applications. The latest
version of the model is described in detail by Mellor (1996).
The second model is a movable nested grid ocean model developed by our
group here at GSO/URI (Ginis et al. 1998, Rowley and Ginis 1999), and
is applied for western North Pacific tropical cyclones. The major
feature of the model is its multiply-nested, movable mesh configuration
which is capable of depicting the ocean response with high resolution
underneath the tropical cyclone. In the vertical, the model consists of
a surface mixed layer and an active layer below, which is divided into
an arbitrary number of numerical layers by means of a sigma
coordinate. This configuration offers some advantages compared with
both layer and level models by providing fine resolution exactly where
it is needed: below the mixed layer. Vertical turbulent mixing in the
model is modeled as a hybrid of the Kraus-Turner-type mixed layer model
and Price's dynamical instability model. By combining the advantages
of those two models, the hybrid scheme simulates vertical mixing in a
very efficient and effective manner. The horizontal diffusion terms
are calculated using the scales of motion resolved by the model and the
local deformation field (Smagorinsky, 1963). The density is calculated
using the modified UNESCO equation of state (Mellor 1991).
We employ one of the premier tropical cyclone forecast systems, the
Geophysical Fluid Dynamics Laboratory (GFDL) model (Kurihara et al.
1997), which was adopted as the official operational hurricane
prediction model at the National Weather Service starting with the 1995
hurricane season. In May 1996, Fleet Numerical Meteorology and Oceanography
Center (FNMOC) started running the Navy
implementation of the GFDL tropical cyclone model, GFDN, in support of
the Joint Typhoon
Warning Center (JTWC). The GFDL model is a primitive
equation model formulated in latitude, longitude, and sigma
coordinates, now being employed with 18 levels in the vertical. The
mesh configuration is based on a triply nested movable grid system
(presently with 1, 1/3 and 1/6 degree resolutions), in which the inner
meshes of finer resolutions are telescopically nested. The model
physics include the cumulus parameterization by Kurihara (1973), a
Monin-Obukhov formulation for surface flux calculations, the Mellor and
Yamada (1974) level 2 turbulence closure scheme for vertical diffusion,
and the Fels-Schwartzkopf radiation package (Schwartzkopf and Fels,
1991).
Multi-Nested Mesh Hurricane Model
Another model developed by Falkovich et al. 1995 is used in this
project to study the interactions of binary tropical cyclones. The
model has five meshes and is capable of simulating two interacting
tropical cyclones. The outermost domain is motionless, while the four
internal meshes (two telescopically nested meshes for each cyclone)
move with storm centers). The numerical algorithm is designed in such
a way that the meshes of different cyclones can cross each other. The
model is based on the primitive equation system in sigma coordinates on
the beta plane, presently configured with 12 levels. Condensation
heating is calculated at resolvable grid scales (Khain, 1988) so that
convection is hydrostatic, but explicit. Horizontal turbulent fluxes
are parameterized using a nonlinear viscosity scheme similar to that of
Kurihara and Tuleya (1974). The vertical turbulent mixing coefficient
for momentum is assumed to be proportional to the vertical wind shear
and calculated as in Khain (1979). All meteorological variables at the
anemometer level and the fluxes of sensible and latent heat and
momentum are calculated using the Deardorff (1972) parameterization.
Back to Tropical Cyclone-Ocean Interaction
Back to the Numerical Modeling Lab page