Part II : Data Assimilation IFS DOCUMENTATION – Cy 36 r 1 Operational implementation 26 January 2010 PART II : DATA ASSIMILATION

Chapter 3 3D variational assimilation (with the first-guess at appropriate time) Chapter 4 Background term Chapter 5 Observation operators and observation cost function (J o) Chapter 6 Background, analysis and forecast errors Chapter 7 Gravity-wave control Chapter 8 Diagnostics Chapter 9 Observation processing Chapter 10 Observation screening Chapter 11 Land-surface analysis Chapter 12 Analysis of sea-ice concentration and sea surface temperature Chapter 13 Data flow References Literary and scientific copyrights belong to ECMWF and are reserved in all countries. This publication is not to be reprinted or translated in whole or in part without the written permission of the Director. Appropriate non-commercial use will normally be granted under the condition that reference is made to ECMWF. The information within this publication is given in good faith and considered to be true, but ECMWF accepts no liability for error, omission and for loss or damage arising from its use. 1.1 Introduction 1.2 Scientific publications 1.3 Brief history of 3D-and 4D-Var in ECMWF operations 1.4 Incremental formulation of variational data assimilation 1.1 INTRODUCTION This documentation of 4D-Var and 3D-FGAT serves as a scientific guide to the data assimilation codes within ECMWF's Integrated Forecasting System (IFS). The documentation is divided into a number of chapters. This first chapter provides an overview of ECMWF's data assimilation system, a brief history of its evolution and a description of the basic scientific formulation. The second chapter describes the practical implementation of the multi-resolution incremental method for 4D-Var data assimilation (used operationally since January 2003, Cy25r3), and the solution algorithm including minimization and preconditioning. The 3D-FGAT configuration as used in the production of ERA-40 (Uppala et al., 2005) and operationally in the so-called Boundary-Condition suite is described in Chapter 3. Thereafter follows a description of the background term (Chapter 4) and a chapter on observation operators and the organisation of observation cost-function calculations for conventional and satellite data (Chapter 5). Chapter 6 deals with the computation and cycling of background and analysis errors and Chapter 7 is on initialization and control of gravity waves. Diagnostic tools for investigation of the performance of the assimilation system are described in Chapter 8. The modules for observation selection, quality control and screening are described in Chapter 9 and Chapter 10. Chapter 11 describes the land surface analysis, including the screen level parameters, the soil analysis and the snow analysis, Chapter 12 describes the sea surface temperature and sea-ice analysis. Finally …