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DATA ASSIMILATION
IFS documentation Front Page
Table of contents
CHAPTER 1 Incremental
formulation of 3D/4D variational assimilation-an overview
CHAPTER 2 3D variational assimilation
CHAPTER 3 4D variational assimilation
CHAPTER 4 Background term
CHAPTER 5 Conventional observational
constraints
CHAPTER 6 Satellite observational
constraints
CHAPTER 7 Background, analysis
and forecast errors
CHAPTER 8 Gravity-wave control
CHAPTER 9 Data partitioning (OBSORT)
CHAPTER 10 Observation screening
CHAPTER 11 Analysis of snow
CHAPTER 12 Land surface analysis
CHAPTER 13 SST and sea-ice analysis
CHAPTER 14 Reduced-rank Kalman filter
Previous Section
8.1 Introduction
In 3D-Var, gravity-wave control is achieved via the techniques of normal-mode initialization (NMI), in 4D-Var a weak constraint digital filter is used. The construction of a high-resolution analysis by combining a high-resolution background with increments defined at lower resolution makes direct use of an incremental form of nonlinear NMI, as in Chapter 1 `Incremental formulation of 3D/4D variational assimilation-an overview' for 3D-Var and Chapter 3 `4D variational assimilation' Eq. (3.3) for 4D-Var. There is an initialization step in creating the low-resolution background field, see Section 2.2. Computation of the penalty term
(see Eq. (1.1)) is based on NMI methods for 3D-Var,
on DFI for 4D-Var.Section 8.2 provides a brief overview of NMI techniques, together with references to scientific papers in which further details can be found. Section 8.3 describes the computation of normal modes and related arrays. Section 8.4 documents the implementation of nonlinear NMI in 3D- and 4D-Var, while Section 8.5 describes the computation of
. Section 8.6
gives an overview of digital filter initialization techniques while
Section 8.7 describes its implementation.Next Section
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20.03.2002 |
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