New Vortex Initialization Scheme for the NCEP's HWRF Model

The HWRF model uses a 6 h predicted vortex from previous cycle as the first guess. We assume the vortex achieves the mass-wind balance during 6 hours model forecast. To have a more realistic initial vortex structure, the location, size and intensity of the first guess vortex are modified based on observations. The new vortex scheme aims to better keep the model balance during the vortex structure modification, in such way that the geopotential is adjusted based on only an increment of the wind change using the gradient wind balance. Besides, the modified vortex is smoothly merged into the environments, so that the only vortex changes without large scale damage. The spin-up/down issue was alleviated by the new vortex initialization scheme in the preliminary result, and more results will be presented during the conference.