Transcript Ensemble Prediction with Perturbed Initial and Lateral

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
 Perturbed Initial conditions (ICs)
 Perturbed lateral boundary conditions (LBCs)
 ICs’ ensemble
 LBCs’ ensemble
 Conclusion & discussion
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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…
Ref: Lorenz, 1982, Atmospheric predictability
experiments with a large numerical model. Tellus
(1982), 34, 505-513.
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Lagged
Ensemble
WRF Model
Flow Chart
 Arakawa-C grid;
 Terrain-following hydrostaticpressure 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.
WRF
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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.
Model set-up
• Time period: 12-27 Dec. 2008;
• Vertical level: 37;
• ICs/LBCs: GFS data;
•
•
•
•
The two-nested domains
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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;
Perturbed Initial Conditions
x  U * Rp  U pUvUh * Rp
(3)
Where, Uh stands for horizontal correlations, Uv for vertical covariances, and Up
for multivariate covariances.
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Background error
Crosssection2
Crosssection1
Model levels
Crosssection1
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Model levels
Crosssection2
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
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b
700hpa T
500hpa T
300hpa T
700hpa GHT
0.4239
0.4829
0.2755
0.4061
0.3867
0.4485
0.1563
0.4263
500hpa GHT
0.4922
0.5428
300hpa GHT
700hpa U
500hpa U
300hpa U
700hpa V
500hpa V
300hpa V
0.4683
0.3737
0.3725
0.275
0.3104
0.4092
0.1904
0.4887
0.3345
0.3475
0.2244
0.2631
0.3882
0.1407
Perturbed Lateral Boundary Conditions (Cntnd)
 Error curve
Error curve(left) & Ration of error growth(right).
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Error growth ratio of temperature at 500hpa from
the physical ensemble RMSEs data(Koracin & Vellore, et. al.)
Perturbed Lateral Boundary Conditions (Cntnd)
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Perturbed pressure at 10-m model level
ICs’ ensemble (50 members)
Pert. ICs only
for D01,
interpolate ICs
from D01 for D02
Domain1
Domain2
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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).
Pert. ICs only for D01
Domain 2
2nd day
10th day
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5th 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.
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).
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ICs’ ensemble (50 members)
Pert. ICs only for D02
With same LBCs
the perturbation in
ICs fades.
2nd day
5th day
Domain 2
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10th day
15th day
LBCs’ ensemble (50 members)
LBCs’ perturbation only for domain 2
Caught the second
front passage.
Oakland
Reno
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Temperature (right) and Geopotential height (left) of domain 2 at 500hPa at Oakland and Reno, CA,
from LBCs’ ensemble (only D02’s LBCs perturbed).
LBCs’ ensemble (50 members)
LBCs’ perturbation only for domain 2
2nd day
10th day
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5th day
15th day
LBCs’ ensemble (50 members)
Talagrand diagram (500hPa)
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More obs. fall
between ensemble
members, less out
the range.
LBCs’ ensemble (50 members)
Talagrand diagram (700hPa)
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More obs. fall
between ensemble
members, less out
the range.
LBCs’ ensemble (50 members)
ICs Ens: spread
1.5/2 times smaller
than RMSE
RMSE vs. spread
300mb
700mb
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500mb
850mb
LBCs Ens: spread
is equivalent with
RMSE.
925mb
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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X a  X b  BHT (HBHT   2 )1[ y o  H ( X b )]
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(4)