Ensemble Prediction with Perturbed Initial and Lateral Boundary Conditions over Complex Terrain
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Ensemble Prediction with Perturbed Initial and Lateral Boundary
Conditions over Complex TerrainJinhua Jiang, Darko Koracin, Ramesh Vellore
Desert Research Institute, Reno, NevadaDesert Research Institute, Reno, Nevada
Weather Impacts Decision Aids (WIDA) Workshop, 2012, Reno, NV
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Outline
Introduction WRF Model Perturbed Initial conditions (ICs) Perturbed lateral boundary conditions (LBCs) ICs’ ensemble LBCs’ ensemble Conclusion & discussion
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Introduction
Where is the uncertainty of NWP from?A Initial-boundary value problemModel frame/structure ( Grid structure, model discretization)Physical parameterizationsDomain size, grid resolutionModel 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
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WRF Model
Flow Chart
WRFWRF
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.
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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;
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Perturbed Initial Conditions
)3(** RpUUURpUx hvp
Where, Uh stands for horizontal correlations, Uv for vertical covariances, and Up for multivariate covariances.
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Background error
Cross-section1
Cross-section2
Cross-section2
Cross-section1
Mod
el le
vels
Mod
el le
vels
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Perturbed Initial Conditions (continued)
Perturbation of temperature (left) and pressure (right).
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Perturbed Lateral Boundary Conditions
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Perturbed Lateral Boundary Conditions (Cntnd)
a b700hpa T 0.4239 0.3867500hpa T 0.4829 0.4485300hpa T 0.2755 0.1563700hpa GHT 0.4061 0.4263
500hpa GHT 0.4922 0.5428
300hpa GHT 0.4683 0.4887700hpa U 0.3737 0.3345500hpa U 0.3725 0.3475300hpa U 0.275 0.2244700hpa V 0.3104 0.2631500hpa V 0.4092 0.3882300hpa V 0.1904 0.1407
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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.)
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Perturbed Lateral Boundary Conditions (Cntnd)
Perturbed pressure at 10-m model level
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ICs’ ensemble (50 members)
Pert. ICs onlyfor 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).
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“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
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Pert. ICs only for D02
Domain2 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).
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Pert. ICs only for D02ICs’ ensemble (50 members)
Domain 2
With same LBCs the perturbation in ICs fades.
2nd day 5th day
10th day 15th day
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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
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LBCs’ ensemble (50 members)LBCs’ perturbation only for domain 2
2nd day 5th day
10th day 15th day
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Talagrand diagram (500hPa)More obs. fall between ensemble members, less out the range.
LBCs’ ensemble (50 members)
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Talagrand diagram (700hPa)More obs. fall between ensemble members, less out the range.
LBCs’ ensemble (50 members)
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RMSE vs. spreadICs Ens: spread 1.5/2 times smaller than RMSE
LBCs Ens: spread is equivalent with RMSE.
700mb 850mb 925mb
300mb 500mb
LBCs’ ensemble (50 members)
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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…
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Thanks for your attention.
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