1 / 29

Massimo Bonavita and Lucio Torrisi CNMCA-UGM, Rome (Italy)

Ensemble data assimilation in an operational context: the experience at the Italian Weather Service. Massimo Bonavita and Lucio Torrisi CNMCA-UGM, Rome (Italy). SREPS Workshop, Bologna 7-8 April 2005. Scope. Current NWP system at CNMCA Motivations CNMCA Hybrid ENKF setup

sabina
Download Presentation

Massimo Bonavita and Lucio Torrisi CNMCA-UGM, Rome (Italy)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ensemble data assimilation in an operational context: the experience at the Italian Weather Service Massimo Bonavita and Lucio Torrisi CNMCA-UGM, Rome (Italy) SREPS Workshop, Bologna 7-8 April 2005

  2. Scope • Current NWP system at CNMCA • Motivations • CNMCA Hybrid ENKF setup • Impact studies on the CNMCA NWP system • Conclusions and developments SREPS Workshop, Bologna 7-8 April 2005

  3. Domain size 385 x 257 Grid spacing 0.25 Deg (28 km) Number of layers 40 Time step and scheme 150 sec, split semi-implicit Forecast range 72 hrs Initial time of model run 00/12 UTC L.B.C. IFS L.B.C. update frequency 3 hrs Initial state CNMCA 3D-PSAS Initialization Digital Filter External analysis None Status Operational Hardware IBM Power4 N° of processors used 32 (Model), 90 (Analysis) CNMCA NWP System SREPS Workshop, Bologna 7-8 April 2005

  4. Domain size 465 x 385 Grid spacing 0.0625 (7 km) Number of layers 35 Time step and scheme 40 s,3 time-lev split-expl Forecast range 60 hrs Initial time of model run 00 UTC Lateral bound. condit. IFS L.B.C. update frequency 3 hrs Initial state EURO-HRM 3D-PSAS Initialization Digital Filter External analysis T,u,v, PseudoRH, SP Special features Filtered topography Status Operational Hardware IBM P690 (ECMWF) N° of processors 120 CNMCA NWP System SREPS Workshop, Bologna 7-8 April 2005

  5. CNMCA NWP System • Intermittent (6-h) data assimilation cycle • Observations: • Synoptic: TEMP, PILOT, SYNOP, SHIP, BUOY • A-synoptic: AMSUA rad, AMDAR-AIREP, AMV, Wind Profilers, QUIKSCAT-ERS2 scatt. winds SREPS Workshop, Bologna 7-8 April 2005

  6. CNMCA NWP System • 3D-PSAS objective analysis in (T,u,v,Pseudo RH, Surf. Press.; Bonavita and Torrisi, 2005) • Parallel (MPI) minimization algorithm of the c.g.d. type of the cost function: SREPS Workshop, Bologna 7-8 April 2005

  7. CNMCA NWP System • Multivariate (T,u,v – Surf. Press.,u,v) correlation functions in spherical geometry • Thermal wind - geostrophic constraint on analysis increments SREPS Workshop, Bologna 7-8 April 2005

  8. Motivations • Known limitation of 3D-Var approach: Stationary forecast error covariances • Possible solution: Ensemble Kalman Filter (Evensen, 1994) • Limited computational cost w.r.t. Extended KF; • Algorithmic simplicity w.r.t. 4DVar: does not require development of a linear and adjoint model; • It does not require linearized evolution of forecast error covariances • It may provide good initial perturbations for ensemble forecasting SREPS Workshop, Bologna 7-8 April 2005

  9. Motivations … but • Limited ensemble size may lead to small ensemble spread • The analysis increments can only occur within the subspace spanned by Pb => O(Nensemble), i.e. very low dimensional w.r.t. model and observations degrees of freedom SREPS Workshop, Bologna 7-8 April 2005

  10. Motivations Possible remedies: • Hybrid EnKF (Hamill & Snyder, 2000; Etherton & Bishop, 2004): • Covariance spatial localization (Houtekamer & Mitchell, 2001) SREPS Workshop, Bologna 7-8 April 2005

  11. CNMCA Hybrid ENKF setup • 24 Perturbed Obs. Members + reference member (unperturbed observations) • Analysis step at half model resolution (0.5°) • Ensemble used to correct only correlation part of covariance product SREPS Workshop, Bologna 7-8 April 2005

  12. HEnKF data assimilation cycle 18 UTC Observations 00 UTC Observations Member j Perturbed Observations 12 UTC B. C. Member j Perturbed Observations 18 UTC B. C. Member j 3DVAR / ENKF using members i≠j Member j 3DVAR / ENKF using members i≠j 6h Forecast 6h Forecast The reference run uses all members to compute the background error correlations and unperturbed observations. SREPS Workshop, Bologna 7-8 April 2005

  13. CNMCA Hybrid ENKF setup Effect of flow-dependent background error covariances SREPS Workshop, Bologna 7-8 April 2005

  14. CNMCA Hybrid ENKF setup SREPS Workshop, Bologna 7-8 April 2005

  15. CNMCA Hybrid ENKF setup SREPS Workshop, Bologna 7-8 April 2005

  16. CNMCA Hybrid ENKF setup • Covariance spatial localization: 1. Horizontal decorrelation length Lc=600Km 2. Vertical decorrelation parameter Kp= 1 SREPS Workshop, Bologna 7-8 April 2005

  17. CNMCA Hybrid ENKF setup Effect of flow-dependent background error covariances (u-wind component 500 hPa) SREPS Workshop, Bologna 7-8 April 2005

  18. CNMCA Hybrid ENKF setup Effect of horizontal covariance localization (Temperature 500 hPa) SREPS Workshop, Bologna 7-8 April 2005

  19. CNMCA Hybrid ENKF setup Effect of horizontal covariance localization(v-wind component, 500 hPa) SREPS Workshop, Bologna 7-8 April 2005

  20. CNMCA Hybrid ENKF setup Effect of vertical covariance localization SREPS Workshop, Bologna 7-8 April 2005

  21. Impact studies: Verification methodology Comparison of forecasts produced from the analyzed fields with SYNOP and RAOB observations.

  22. Impact studies SREPS Workshop, Bologna 7-8 April 2005

  23. Impact studies SREPS Workshop, Bologna 7-8 April 2005

  24. Impact studies SREPS Workshop, Bologna 7-8 April 2005

  25. Impact studies SREPS Workshop, Bologna 7-8 April 2005

  26. Conclusions and future plans • Current CNMCA HEnKF forecast skill is overall comparable to pure 3DVAR assimilation. • HEnKF have been set up based on recent literature and heuristic assumptions. SREPS Workshop, Bologna 7-8 April 2005

  27. Conclusions and future plans • Careful tuning of HEnKF parameter: , Lc, Kp • Use of ensemble covariances, not just correlations • System is intrinsically suitable for parallelization but still expensive in terms of billing units: Nensx(analysis and t+6h forecasts) !  further reduction of analysis resolution, but tradeoff with realistic covariance structures SREPS Workshop, Bologna 7-8 April 2005

  28. Conclusions and future plans • Explore the possibility of using ensemble members for short range EPS SREPS Workshop, Bologna 7-8 April 2005

  29. Thank you! SREPS Workshop, Bologna 7-8 April 2005

More Related