The nested grid model

The nested grid model (NGM) consists of a stereographic hemispheric grid with the option of one or two interior rectangular grids, each of successively smaller area and finer horizontal resolution. The location and number of the vertical sigma levels is flexible, as is the basic horizontal resolution. Second-order accurate finite-difference formulas are used, in a two-step Lax-Wendroff procedure. Special initial treatments are used to reduce spurious gravity waves from the Himalayas, and to insure symmetry about the Equator.