Some aspects of dynamic initialization using real tropical wind data

Abstract

In this study an iterative initialization scheme suitable for tropical regions is designed, tested and used as an initialization vehicle in an experiment involving real tropical data. The model equations for the initialization scheme are the so called shallow water equations bounded by rigid walls at the north and south boundaries. The advective terms of the model equations are evaluated using the quasi-lagrangian scheme. This advective scheme was modified following Kanamitsu [18] so as to prevent the occurrence of the so called two grid distance waves. Time differencing scheme in the time integration (10 time steps forward ans 10 time steps backward) of the model equations is the Euler-backward type. The initialization scheme is found to conserve mean total energy, mean potential vorticity and mean square potential vorticity following an air parcel.

The designed initialization scheme was used in an initialization experiment involving real tropical wind data. In this experiment, we started with observed wind field (rotational plus irrotational component) and the geopotential computed from non linear balance equation. The results from this experiment show that the initially imbalanced motion and mass fields tend to settle down to some form of balance during the initialization process. It is further noted that the “initialized” motion fields have more organized streamline pattern than the original wind field. Also, the streamline patterns shown that the difference between the initialized and original motion fields is small. This is desirable for any initialization scheme.