Normal Mode Initialization for a Multilevel Grid-Point Model. Part II: Nonlinear Aspects

Abstract

In Part II of this paper, we describe the nonlinear normal mode initialization applied to the ECMWF multilevel global grid-point model and show that the procedure is highly successful in eliminating spurious high-frequency oscillations from forecasts made by the model. We determine the number of vertical modes that can be included in the procedure and demonstrate insensitivity to minor changes in the definitions of the modes. Attempts to include physical parameterizations within the initialization procedure are described as are the problems which arise with such attempts. It is shown that adiabatic nonlinear initialization is adequate to eliminate high-frequency gravity mode oscillations from a forecast by a model which includes non-adiabatic processes.