Page 1 The Construction and Use of Linear Models in Large-scale Data Assimilation Tim Payne Large-Scale Inverse Problems and Applications in the Earth Sciences October 24th 2011
Page 2 © Crown copyright 2011 Part I. The Construction of Linear Models in Data Assimilation
Page 3 © Crown copyright 2011 Notation
Page 4 © Crown copyright 2011 Update-Prediction Cycle
Page 5 © Crown copyright 2011 First Strategy – exact evolution of covariances
Page 6 © Crown copyright 2011 Second strategy – EKF using tangent-linear
Page 7 © Crown copyright 2011 Third strategy – EKF using best linear approximation
Page 8 © Crown copyright 2011 Explicit formula for best linear approximation
Page 9 © Crown copyright 2011 Basic properties of best linear approximation
Page 10 © Crown copyright 2011 Cloud function
Page 11 © Crown copyright 2011 Smith Cloud Scheme with ‘ad hoc’ Regularisation
Page 12 © Crown copyright 2011 Smith Cloud Scheme with ‘Optimal’ Regularisation
Page 13 © Crown copyright 2011 Incremental 4D-Var
Page 14 © Crown copyright 2011 Options for linearisation step required for incremental 4D-Var
Page 15 © Crown copyright 2011 Gain matrix implied by each option
Page 16 © Crown copyright 2011 Advantage of BLA over TL in incremental 4D-Var
Page 17 © Crown copyright 2011 Pseudo Chain-rule for best linear approximation
Page 18 © Crown copyright 2011 Use of best linear approximation in EKF
Page 19 © Crown copyright 2011 The prior covariance implied by different approximations
Page 20 © Crown copyright 2011 Prior covariance using best linear estimate
Page 21 © Crown copyright 2011 Prior covariance using the best linear estimate always underestimates the true prior
Page 22 © Crown copyright 2011 The Duffing Map
Page 23 © Crown copyright ,000 iterates of Duffing Map
Page 24 © Crown copyright 2011 Reminder of EKF algorithm
Page 25 © Crown copyright 2011 Prior covariance for Duffing Map
Page 26 © Crown copyright 2011 Mean square analysis error in Duffing map: TL and best linear estimate compared
Page 27 © Crown copyright 2011 Part II. The Use of Linear Models in Data Assimilation
Page 28 © Crown copyright 2011 Linearisation error in 4D-Var as used in real numerical weather prediction models
Page 29 © Crown copyright 2011
Page 30 © Crown copyright 2011 Linear model for evolution of increments
Page 31 © Crown copyright 2011 Linearisation error as a stochastic error
Page 32 © Crown copyright 2011 Issues in forming EKF
Page 33 © Crown copyright 2011 Signal model for system with time correlated linearisation error
Page 34 © Crown copyright 2011 EKF with time correlated linearisation error
Page 35 © Crown copyright 2011 Parameters for filter including linearistion error
Page 36 © Crown copyright 2011 Example: L95, nearly perfect full model, persistence for linear model
Page 37 © Crown copyright 2011 Example: L95, nearly perfect full model, persistence for linear model, results
Page 38 © Crown copyright 2011 Variational version: weak constraint 4D-Var allowing for time correlated linearisation error
Page 39 © Crown copyright 2011 Remarks on variational form
Page 40 © Crown copyright 2011 Long window weak constraint 4D-Var allowing for linearisation error, same example
Page 41 © Crown copyright 2011 Summary to Part I
Page 42 © Crown copyright 2011 Summary to Part II
Page 43 © Crown copyright 2011 The End