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A new 4-dimensional variational data assimilation system for WRF. Juan Zhao , Bin Wang LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing. 2008-07-01. University Allied Workshop. Outline. Introduction to a new DA approach (HSP-4DVAR)
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A new 4-dimensional variational data assimilation system for WRF Juan Zhao , Bin Wang LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 2008-07-01 University Allied Workshop
Outline • Introduction to a new DA approach (HSP-4DVAR) • Observing system simulation experiment (OSSE) • Summary University Allied Workshop
Outline • Introduction to a new DA approach (HSP-4DVAR) • Observing system simulation experiment (OSSE) • Summary University Allied Workshop
Introduction to HSP-4DVAR 4DVAR N*N The huge computing cost of the iterative procedure based on the adjoint technique greatly limits the wide applications of traditional 4DVAR ! Cost function of 4DVAR (incremental form): N-dimensional model space (N:106~108) Calculate by making the nonlinear optimal iteration: An effective and efficient 4DVAR adjoint (ECMWF,2002) University Allied Workshop
Introduction to HSP-4DVAR HSP-4DVAR Historical Sample Projection (HSP)-4DVAR (Bin Wang et al, 2008) new cost function: m-dimensional sample space Abandon adjoint model Avoid making nonlinear optimal iteration m~102 calculate explicitly: ? University Allied Workshop
Introduction to HSP-4DVAR Estimation of B matrix Utilize historical forecast samples to estimate B In model space In sample space University Allied Workshop
Introduction to HSP-4DVAR Estimation of B matrix not full rank (rank = m - 1) underestimation of B University Allied Workshop
Introduction to HSP-4DVAR Estimation of B matrix Take Xb as one of the samples ! full rank (rank = m) University Allied Workshop
Introduction to HSP-4DVAR localization Purpose: to filter the false covariance between one point and another far point in B ( : Schur filtering operator) • Much more timesaving than EnKF localization Use the analysis as the only sample University Allied Workshop
Introduction to HSP-4DVAR Analysis——in the middle of window new 4DVAR traditional 4DVAR 03 06 00 mean value theorem (Math) Xa Xa 3DVAR 03 06 00 Xa University Allied Workshop
Outline • Introduction to a new DA approach(HSP-4DVAR) • Observing system simulation experiment (OSSE) • Summary University Allied Workshop
OSSE—— experiment design Experiment design • Domain configuration: 189×89×29, 30km • TRUE—— forecasts from ECMWF global analysis (2.50×2.50) in the beginning of the assimilation window • CTL—— forecasts from background field; background field is produced from a 48h forecast with NCEP/NCAR reanalysis (10×10) at 48h prior to the beginning of the assimilation window • ASS—— forecasts from analysis field • Simulated obs: temperature (T) on model level 1, 10, 19, 28, interpolated from ‘TRUE’ University Allied Workshop
OSSE—— experiment results Experiment results assimilation window -03 00 03 06 12 18 24 CTL ASS_middle (ASS) ASS_start University Allied Workshop
OSSE—— experiment results 00h RMSE ASS : ASS_middle University Allied Workshop
OSSE—— experiment results 03h RMSE University Allied Workshop
OSSE—— experiment results 06h RMSE University Allied Workshop
OSSE—— experiment results 12h RMSE University Allied Workshop
OSSE—— experiment results 00h RMSE ASS_start = ASS_start — CTL ASS_middle = ASS_middle — CTL < 0 better > 0 worse
OSSE—— experiment results 03h RMSE University Allied Workshop
OSSE—— experiment results 06h RMSE University Allied Workshop
OSSE—— experiment results 12h RMSE University Allied Workshop
OSSE—— experiment results CTL 06h TRUE ASS precipitation ASS : ASS_middle University Allied Workshop
OSSE—— experiment results CTL 12h TRUE ASS precipitation University Allied Workshop
OSSE—— experiment results CTL 18h TRUE ASS precipitation University Allied Workshop
OSSE—— experiment results CTL 24h TRUE ASS precipitation University Allied Workshop
Outline • Introduction to a new DA approach(HSP-4DVAR) • Observing system simulation experiment (OSSE) • Summary University Allied Workshop
Summary (1) • The new WRF HSP-4DVAR system performs well • abandon the adjoint technique • avoid making the nonlinear optimal iteration very time-saving • B is flow-dependent implicitly in the assimilation window explicitly from window to window • A promising approach to be applied in operational NWPs University Allied Workshop
Summary (2) • Plans: • More experiments to test the new DA system (conventional and unconventional obs data) • Further improvement of B (analog prediction sample, EOF technique……) University Allied Workshop
Thank you! Comments and questions are welcome! University Allied Workshop