Kurihara, Y., M. A. Bender, and R. J. Ross, 1993: An initialization
scheme of hurricane models by vortex specification. Monthly Weather
Review, 121(7), 2030-2045.
Abstract: A scheme is presented to improve the representation of
a tropical cyclone in the initial condition of a high-resolution hurricane
model. In the proposed method, a crudely resolved tropical cyclone in the
large-scale analysis is replaced by a vortex that is properly specified
for use in the prediction model.
Appropriate filters are used to remove the vortex from the large-scale
analysis so that a smooth environmental field remains. The new specified
bogus vortex takes the form of a deviation from the environmental field
so that it can be easily merged with the latter field at the correct position.
The specified vortex consists of both axisymmetric and asymmetric components.
The symmetric component is generated by the time integration of an axisymmetric
version of the hurricane prediction model. This ensures dynamical and thermodynamical
consistency in the vortex structure, including the moisture field, and
also compatibility of the vortex with the resolution and physics of the
hurricane model. In the course of the integration of the axisymmetric model,
the tangential wind component is gradually forced to a target wind profile
determined from observational information and empirical knowledge. This
makes the symmetric vortex a good approximation to the corresponding real
tropical cyclone. The symmetric flow thus produced is used to generate
an asymmetric wind field by the time integration of a simplified barotropic
vorticity equation, including the beta effect. The asymmetric wind field,
which can make a significant contribution to the vortex motion, is then
added to the symmetric flow. After merging the specified vortex with the
environmental flow, the mass field is diagnosed from the divergence equation
with an appropriately controlled time tendency. The wind field remains
unchanged at this step of initialization.
Since the vortex specified by the proposed method is well adapted to the
hurricane prediction model, problems of initial adjustment and false spinup
of the model vortex, a long-standing difficulty in the dynamical prediction
of tropical cyclones, are alleviated. It is anticipated that the improvement
of the initial conditions can reduce the error in hurricane track forecasting
and extend the feasibility of tropical cyclone forecasting to intensify
change.