1. Ensemble Prediction with Perturbed Initial and Lateral Boundary Conditions over Complex Terrain Jinhua Jiang, Darko Koracin, Ramesh Vellore Desert Research Institute, Reno, Nevada Weather Impacts Decision Aids (WIDA) Workshop, 2012, Reno, NV

2. Page  2 Outline  Introduction  WRF Model  Perturbed Initial conditions (ICs)  Perturbed lateral boundary conditions (LBCs)  ICs’ ensemble  LBCs’ ensemble  Conclusion & discussion

3. Page  3 Introduction Where is the uncertainty of NWP from?  A Initial-boundary value problem  Model frame/structure （ Grid structure, model discretization ）  Physical parameterizations  Domain size, grid resolution  Model topography, SST, soil moisture… “KNOW WHAT YOU KNOW, KNOW WHAT YOU DO NOT KNOW.” “ 知之为知之，不知为不知 “ Ref: Lorenz, 1982, Atmospheric predictability experiments with a large numerical model. Tellus (1982), 34, 505-513. Lagged Ensemble

4. Page  4 WRF Model Flow Chart WRF  Arakawa-C grid;  Terrain-following hydrostatic- pressure vertical coordinate (η);  Flux-form Euler Equations;  Discretization: Runge-Kutta scheme, (Wicker & Skamarock(2002) time splitting for acoustic integration;  Gravity wave/Vertical velocity: Rayleigh Damping layer. Ref: Skamarock, W. C., J. B. Klemp, J. Dudhia, et al. 2008, A Description of the Advanced Research WRF Version 3. NCAR Technical Note. NCAR/TN-475+STR.

5. Page  5 Model set-up The two-nested domains Time period: 12-27 Dec. 2008; Vertical level: 37; ICs/LBCs: GFS data; 0-180hr, 0.5° x 0.5° ; 180-384 hrs, 2.5 x 2.5. PBL: Mellor-Yamada-Janjic; Radiation: RRTM LW scheme, Goddard SW scheme; Land surface: Unified Noah LSM; Microphysics: Morrison 2-moment scheme;

6. Page  6 Perturbed Initial Conditions  Where, U h stands for horizontal correlations, U v for vertical covariances, and U p for multivariate covariances.

7. Page  7 Background error Cross- section1 Cross- section2 Cross- section1 Model levels

8. Page  8 Perturbed Initial Conditions (continued) Perturbation of temperature (left) and pressure (right).

9. Page  9  Perturbed Lateral Boundary Conditions

10. Page  10 Perturbed Lateral Boundary Conditions (Cntnd) ab 700hpa T0.42390.3867 500hpa T0.48290.4485 300hpa T0.27550.1563 700hpa GHT0.40610.4263 500hpa GHT0.49220.5428 300hpa GHT0.46830.4887 700hpa U0.37370.3345 500hpa U0.37250.3475 300hpa U0.2750.2244 700hpa V0.31040.2631 500hpa V0.40920.3882 300hpa V0.19040.1407

11. Page  11 Perturbed Lateral Boundary Conditions (Cntnd)  Error curve Error curve(left) & Ration of error growth(right). Error growth ratio of temperature at 500hpa from the physical ensemble RMSEs data(Koracin & Vellore, et. al.)

12. Page  12  Perturbed Lateral Boundary Conditions (Cntnd) Perturbed pressure at 10-m model level

13. Page  13 ICs’ ensemble (50 members) Pert. ICs only for D01, interpolate ICs from D01 for D02 Domain1 Domain2 Temperature (right) and Geopotential height (left) of domain 1 and domain 2 at 500hPa at OAK, CA, from ICs’ ensemble (only D01 perturbed).

14. Page  14 “Spaghetti” plots of the 238 K (blue lines) and 258 K (green lines) air temperature from domain 2 for forecast times of 2, 5, 10 and 15 days. Domain 2 Pert. ICs only for D01 2nd day 5th day 10th day 15th day

15. Page  15 Pert. ICs only for D02 Domain2 ICs’ ensemble (50 members) Difference: LBCs for domain 2 (size: 3708 km X 3708 km) Temperature (right) and Geopotential height (left) of domain 2 at 500hPa at OAK, CA, from ICs’ ensemble (only D02 perturbed).

16. Page  16 Pert. ICs only for D02 ICs’ ensemble (50 members) Domain 2 With same LBCs the perturbation in ICs fades. 2nd day 5th day 10th day 15th day

17. Page  17 LBCs’ ensemble (50 members) LBCs’ perturbation only for domain 2 Temperature (right) and Geopotential height (left) of domain 2 at 500hPa at Oakland and Reno, CA, from LBCs’ ensemble (only D02’s LBCs perturbed). Caught the second front passage. Oakland Reno

18. Page  18 LBCs’ ensemble (50 members) LBCs’ perturbation only for domain 2 2nd day 5th day 10th day 15th day

19. Page  19 Talagrand diagram (500hPa) More obs. fall between ensemble members, less out the range. LBCs’ ensemble (50 members)

20. Page  20 Talagrand diagram (700hPa) More obs. fall between ensemble members, less out the range. LBCs’ ensemble (50 members)

21. Page  21 RMSE vs. spread ICs Ens: spread 1.5/2 times smaller than RMSE LBCs Ens: spread is equivalent with RMSE. 700mb 850mb 925mb 300mb500mb LBCs’ ensemble (50 members)

22. Page  22 Conclusion & discussion For the limited-area ensemble, e.g. a domain size ~ 4000kmX4000km: Error in out-domain/lateral boundary conditions is important. Small error in initial conditions fades after two days; Perturbation in lateral boundary conditions play a main role later on. More issues to be addressed: ? Different domain size, ? Multi-models (different grid structure, discretization) ? Model SST/Soil moisture & temperature/Topography ? Physical parameterizations ? Ensemble member size…

23. Page  23 Thanks for your attention.

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