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 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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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


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.


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.


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


Perturbed Initial Conditions

Where, Uh stands for horizontal correlations, Uv for vertical covariances, and Up for multivariate covariances.


Background error

Cross-section2

Cross-section1

Cross-section2

Model levels

Cross-section1

Model levels


Perturbed Initial Conditions (continued)

Perturbation of temperature (left) and pressure (right).


Perturbed Lateral Boundary Conditions


Perturbed Lateral Boundary Conditions (Cntnd)


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.)


Perturbed Lateral Boundary Conditions (Cntnd)

Perturbed pressure at 10-m model level


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).


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.


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).


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


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).


LBCs’ ensemble (50 members)

LBCs’ perturbation only for domain 2

2nd day

5th day

10th day

15th day


LBCs’ ensemble (50 members)

More obs. fall between ensemble members, less out the range.

Talagrand diagram (500hPa)


LBCs’ ensemble (50 members)

More obs. fall between ensemble members, less out the range.

Talagrand diagram (700hPa)


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


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…


Thanks for your attention.


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