Normal mode initialization

The baroclinic primitive equation models used for short‐ and medium‐range weather forecasting admit undesirable high‐frequency gravity waves. The gravity waves are excited by initial imbalances between the observed wind and mass fields and by inconsistencies between model and atmosphere. Over the years, many initialization techniques have been devised to balance the initial state, but without notable success. The recent introduction of normal mode initialization techniques has, to a large degree, solved the problem. The present review will discuss the development of the technique from first principles, introduce the slow manifold concept, and discuss successful applications and remaining problems.