The control of gravity waves in data assimilation

The need to control gravity waves in data assimilation and the general concept of initialization are discussed. The basic method of non-linear normal-mode initialization is introduced, and aspects of its implementation in models are presented, covering the vertical and horizontal modal decomposition, implicit initialization and diabatic initialization. The control of gravity waves in the ECMWF variational data assimilation system is described. An introduction to the alternative method of digital filtering is also given.

Contents

1. Introduction
2. Non-linear normal-mode initialization
3. Control of gravity waves in the ECMWF variational data assimilation
4. Digital filtering
5. Appendix
   • A. Definition of operators for the ECMWF vertical finite-difference scheme
   • B. The Lamb wave
   • C. The non-recursive implementation of the recursive filter
6. References