Development of a high resolution operational model at JMA

Kengo Matsubayashi Numerical Prediction Division, Japan Meteorological Agency

with Kohei Kawano, Tabito Hara, Kohei Aranami, Hiroshi Kusabiraki,Haruka Kurahashi and Junichi Ishida

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August 19, 2014The World Weather Open Science Conference 2014

Montreal, Canada

Global Meso Local

ObjectivesShort- and

Medium-range forecast

Disaster reduction

Short-range forecast

Aviation forecastDisaster

prevention

NWP model Global SpectralModel(GSM)

Meso-Scale Model(MSM)

Local Forecast Model (LFM)

Horizontal resolution

TL959 (0.1875 deg)

5 km(817x611)

2 km(1581x1301)

Verticallevels / Top

1000.01 hPa

5021.8 km

6020.2 km

ForecastHours

(Initial time)

84 hours(00, 06, 18 UTC)

264 hours(12 UTC)

39 hours(every 3 hours)

9 hours(every hour)

Initial Condition

Global Analysis(4D-Var)

Meso-scale Analysis(4D-Var)

Local Analysis (3D-Var)

ForecastDomain

NWP systems at JMA (deterministic)

Meso

Local

Global

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Current operational NWP systems at JMA• A high resolution

convection-permitting regional NWP system (Local NWP system) has been operated since August 2012.

• It’s purpose is providing information on aviation weather and disaster prevention.

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Basic design of the Local NWP system• The Local NWP system provides 9-hour period forecasts every hour.• In the system design, frequent updates of forecasts (24 times a day!!)

assimilating the latest observation are highly emphasized.

• The Local NWP system consists of two subsystems– NWP model: The Local Forecast Model

(LFM) has a 2-km horizontal grid spacing and 60 vertical layers.

– high resolution to permit explicit convection

– Data assimilation system: The Local Analysis (LA) employs an analysis system based on the three dimensional variational data assimilation (3D-Var) at a 5-km resolution.

Forecast:1581x1301 (2km grids)Analysis:633x522 (5km grids)

High mountains and valleys are more High mountains and valleys are more realistically resolved. realistically resolved.

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1581x1301 with 2km grids.operational domain

Domain of the Local NWP system

40N

30N

40N

30N

A region of the same size (for reference)

Montreal

2600km

3160km

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Advantage of LFM

The LFM has considerable potential to represent the shape of precipitation and its peak values more accurately.

1-hour accumulated precipitation amounts until 1700UTC on July 11 2012

mm/h

max 60mm/h

500km

600km

We are operating LFM, but…• Current dynamical core (JMA-NHM) is too old– Using matured but old technics (developed mainly in 1980s)

• Insufficient accuracy such as no mass conservation, leap-frog scheme

• Forecasts are quite sensitive to numerical diffusion– We do not know what value is the best for coefficients of numerical

diffusion because we have no established way to find the best parameter (just based on empirical)

– Not necessarily compatible with the current computer trend

– Almost no room left for further developing• Fairly convoluted codes• Codes for physics cannot be separated

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DEVELOPMENT OF A NEW DYNAMICAL CORE

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Development of a new dynamical coreMotivation

• A new nonhydrostatic dynamical core named “ASUCA” is under development aiming at1. Higher accuracy, stability

e.g. exact conservation of mass

2. Exclusion of artificial parameters (e.g. numerical diffusion coefficient) as much as possible

3. Higher efficiency on massive parallel scalar multi-core architecture

4. Keeping the codes well structured possible to facilitate the developments and long term maintenance

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The specification comparison of the dynamical core between ASUCA and JMA-NHM

ASUCA JMA-NHM

Governing equations Flux formFully compressible equations

Quasi flux formFully compressible equations

Prognostic variables ρu, ρv, ρw, ρθ, ρ ρu, ρv, ρw, θ, p

Spatial discretization Finite volume method Finite difference Method

Time integration Runge-Kutta 3rd

(long and short)Leapflog with time filter (long)Forward backward (short)

Treatment of sound Conservative Split explicit Split explicit

Advection Combining 3rd and 1st order upwind with flux limiter by Koren(1993)

4th (hor.) and 2nd(ver.) order with advection correction

Numerical diffusion None 4th order linear and nonlinear diffusion

Treatment of rain-drop Time-split Box-Lagrangian

Coordinate Generalized coordinate orConformal mapping + Hybrid-Z

Conformal mapping (hor.)Hybrid – Z (ver.)

Grid Arakawa-C (hor.)Lorentz (ver.)

Arakawa-C (hor.)Lorentz (ver.)

C : Mass conservation A : Higher accuracy S : Higher stability

C

C

C

A

M : Monotonicity

S

A MC

A

C

Mass conservation• Lack of mass conservation might lead to generate errors in the predicted

pressure fields.

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The total mass is obviously smaller than the reference, and the pressure field is different from the reference.

JMA-NHM

MSL pressure forecastDifference from a reference

pressure field

ASUCASum of MSL pressure difference from given reference over the domain is zero.

• The total mass tendency over the domain should be equal to that given by LBC if mass conservation is exactly satisfied.

• If mass does not conserve, accurate pressure field and resulting synoptic scale phenomenon cannot be reproduced.

4th order4th order + adv. correction4th order + adv. correction+ 4th linear diffusion4th order + adv. correction+ 4th linear diffusion+ nonlinear diffusion

Advection scheme

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• JMA-NHM– Based on 4th order scheme– Advection correction– 4th linear diffusion– Nonlinear diffusion

adopted in JMA-NHM

Cycle advection test in a constant velocity field.Green line is the result of after two cycles.

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Advection scheme• Combining– 3rd order upwind in smooth regions

• Higher accuracy, non-monotonicity （ Godunov’s theorem ）

– 1st order upwind in sharp gradient regions• Monotonicity , lower accuracy

with using flux limiter function proposed by Koren(1993)

Koren(1993)

Monotonicity is preserved, no overshoot and no undershoot appeared.

Cycle advection test in a constant velocity field.Green line is the result of after two cycles.

Warm bubble test

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potential temperature

10km

Initial bubble size: 4000mPT perturbation: +2K

Warm bubble test

In a courser resolution, the position and the shape of the bubble are not well predicted for the poor accuracy of the adv. scheme.And they are quite sensitive to the strength of the numerical diffusion.

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dx = 125m

JMA-NHM w/o diffusion

ASUCA

JMA-NHM

dz = 125m in all cases.dx = 1000m

JMA-NHM w/ diffusion

ASUCA

Current status of ASUCA• Main part of the developments of dynamical core has been

completed.• Physical processes equivalent to or more enhanced than those of

current LFM have been implemented. • Basic performance is similar to or better than that of JMA-NHM.• ASUCA will be operational as LFM later in 2014 along with a

3DVAR system based on ASUCA.

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ASUCA JMA-NHM Obs.

Thank you for your attention.

• To archive higher efficiency– kij-ordering– reduce the number of MPI communication

• Implementation of physical processes– Physics library

• Pre-operational run – Large acoustic wave caused by the imbalance of 3DVar

• Convection in high resolution model– Convective initiation is sensitive to the high wave number modes.– The high wave number modes have a sensitivity to the diffusivity in advection

schemes.– Even in 2km horizontal resolution, the initiation of convection is not

necessarily resolved.– We employ parameterization for convective initiation.

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Other topics