A GLOBAL NUMERICAL WEATHER PREDICTION MODEL WITH VARIABLE RESOLUTION

A conformal transformation suggested by F. Schmidt is followed to impl ement a global spectral model with variable resolution. A conformal ma pping is defined from a physical sphere (like the earth) to a transfor med (computational) sphere. The model equations are discretized on the computational sphere, and the conventional spectral technique is appl ied to march forward in time. Two types of transformations are investi gated in the present study, namely the rotation and the stretching tra nsformation. Application of the stretching transformation leads to fin er resolution in the meridional direction; however, due to the spheric al geometry, the resolution becomes finer in the latitudinal direction also, and furthermore. the rotation can be used to relocate the model poles. The idea is now to rotate the north pole and refine the resolu tion around the new north pole by applying the stretching transformati on. A multilevel global spectral model is formulated from the current Florida State University global spectral model to implement the total (rotation followed by stretching) transformation. The control run in t his study is a conventional T-170 resolution global spectral model. Th e transformed T-83 resolution global spectral model is used to study H urricane Andrew. The performance of the transformed model is clearly s een to be improved in describing the structure, intensity, and motion of the hurricane over the conventional T-85 resolution spectral model. The computational cost for the transformed model is approximately one -half the cost for the conventional T-170 model. The conformal transfo rmation technique can be thus used as a viable alternative to the limi ted-area models.