Nonlinear Normal Mode Initialization of a Limited Area Model Using Nonstationary Rossby Modes

摘要

For the application of the nonlinear normal mode method to the initialization of a limited area prediction model, the construction of the normal modes of the linearized model equations is treated. Instead of setting Coriolis parameter equal to a constant value in the equations, leading to stationary Rossby modes, a simple extension, by modifying the linearized model equations so that they admit solutions with nonzero Rossby frequencies, is considered. The results are compared with those using a nonlinear normal mode initialization with constant Coriolis parameter. They show that the two methods are virtually identical in their effect upon the initial fields and upon their development during the first hours of the forecast.