Introduction to Initialization

Abstract

The spectrum of atmospheric motions is vast, encompassing phenomena having periods ranging from seconds to millennia. The motions of interest to the forecaster have timescales greater than a day, but the mathematical models used for numerical prediction describe a broader span of dynamical features than those of direct concern. For many purposes these higher frequency components can be regarded as noise contaminating the motions of meteorological interest. The elimination of this noise is achieved by adjustment of the initial fields, a process called initialization. In this chapter, the fundamental equations are examined and the causes of spurious oscillations are elucidated. The history of methods of eliminating high-frequency noise is recounted and various initialization methods axe described. The normal mode initialization method is described, and illustrated by application to a simple mechanical system, the swinging spring.