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Ensemble Prediction with Perturbed Initial and Lateral Boundary Conditions over Complex Terrain

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. Outline. Introduction WRF Model

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Ensemble Prediction with Perturbed Initial and Lateral Boundary Conditions over Complex Terrain

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  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. Outline • Introduction • WRF Model • Perturbed Initial conditions (ICs) • Perturbed lateral boundary conditions (LBCs) • ICs’ ensemble • LBCs’ ensemble • Conclusion & discussion

  3. Introduction “KNOW WHAT YOU KNOW, KNOW WHAT YOU DO NOT KNOW.” “知之为知之，不知为不知“ 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… Lagged Ensemble Ref: Lorenz, 1982, Atmospheric predictability experiments with a large numerical model. Tellus (1982), 34, 505-513.

  4. WRF Model • 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. Flow Chart WRF 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. Model set-up • 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; The two-nested domains

  6. Perturbed Initial Conditions Where, Uh stands for horizontal correlations, Uv for vertical covariances, and Up for multivariate covariances.

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

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

  9. Perturbed Lateral Boundary Conditions

  10. Perturbed Lateral Boundary Conditions (Cntnd)

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

  13. ICs’ ensemble (50 members) Pert. ICs only for D01, interpolate ICs from D01 for D02 Domain1 Domain1 Domain2 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. Pert. ICs only for D01 2nd day 5th day Domain 2 10th day 15th day “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.

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

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

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

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

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

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

  21. LBCs’ ensemble (50 members) ICs Ens: spread 1.5/2 times smaller than RMSE RMSE vs. spread 300mb 500mb LBCs Ens: spread is equivalent with RMSE. 925mb 850mb 700mb

  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. Thanks for your attention.

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