Higher Resolution Operational Models

Major U.S. High-Resolution Mesoscale

Models (all non-hydrostatic)• WRF-ARW (developed at NCAR)

• NMM-B (developed at NCEP Environmental Modeling Center)

• COAMPS (U.S. Navy)

• MM5 (NCAR, old, replaced by WRF)

• RAMS (Regional Atmospheric Modeling System, Colorado State)

• ARPS (Advanced Regional Prediction System): Oklahoma

Operational Mesoscale Model History in US

• Early: LFM, NGM (history)

• Eta (mainly history)

• MM5: Still used by some, but mainly phased out

• NMM- Main NWS mesoscale model, updated Eta model. Sometimes called WRF-NMM and NAM.

• WRF-ARW: Heavily used by research and some operational communities.

• NMM replaced by NMM-B

WRF and NMM

History of WRF model• An attempt to create a national mesoscale prediction

system to be used by both operational and research communities.

• A new, state-of-the-art model that has good conservation characteristics (e.g., conservation of mass) and good numerics (so not too much numerical diffusion)

• A model that could parallelize well on many processors and easy to modify.

• Plug-compatible physics to foster improvements in model physics.

• Designed for grid spacings of 1-10 km

WRF Modeling System

Obs Data,Analyses

Post Processors,Verification

WRF Software Infrastructure

Dynamic Cores

Mass Core

NMM Core…

Standard Physics Interface

Physics Packages

StaticInitialization

3DVAR DataAssimilation

Two WRF Cores• ARW (Advanced Research WRF) • developed at NCAR• Non-hydrostatic Numerical Model (NMM) Core developed at

NCEP• Both work under the WRF IO Infrastructure

NMM ARW

The NCAR ARW Core Model:(See: www.wrf-model.org)

Terrain following vertical coordinate two-way nesting, any ratio Conserves mass, entropy and scalars using up to

6th order spatial differencing equ for fluxes. Very good numerics, less implicit smoothing in numerics.

NCAR physics package (converted from MM5 and Eta), NOAH unified land-surface model, NCEP physics adapted too

NWS NMM1—The NAM RUN• Run every six hours over N. American and adjacent

ocean• Run to 84 hours at 12-km grid spacing.• Uses the Grid-Point Statistical Interpolation (GSI)

data assimilation system (3DVAR)• Start with GDAS (GFS analysis) as initial first guess

at t-12 hour (the start of the analysis cycle)• Runs an intermittent data assimilation cycle every

three hours until the initialization time.

1-Non-hydrostatic mesoscale model, NAM: North American Mesoscale run

NMM-B

• Hybrid sigma-pressure vertical coordinate

• 60 levels

• Betts-Miller-Janjic convective parameterization scheme

• Mellor-Yamada-Janji boundary layer scheme

NMM-B Details

• One-way nested forecasts computed concurrently with the 12-km NMM-B parent run for

– CONUS (4 km to 60 hours)

– Alaska (6 km to 60 hours)

– Hawaii (3 km to 60 hours)

– Puerto Rico (3 km to 60 hours)

– For fire weather, moveable 1.33-km CONUS and 1.5-km Alaska nests are also run concurrently (to 36 hours).

• A change in horizontal grid from Arakawa-E to Arakawa-B grid, which speeds up computations without degrading the forecast

13

September 2011 NAM-B Upgrade

New NAM• NEMS based NMMB• B-grid replaces E-grid• Parent remains 12 km to 84 hr• Four Fixed Nests Run to 60 hr

– 4 km CONUS nest– 6 km Alaska nest– 3 km HI & PR nests

• Single placeable 1.33km or 1.5 km Single placeable 1.33km or 1.5 km FireWeather/IMET/DHS run to 36hrFireWeather/IMET/DHS run to 36hr

NMMB 4-km Conus

NAM

• Generally less skillful than GFS, even over U.S.

• Generally inferior to WRF-ARW at same resolution (more diffusion and smoothing, worse numerics)

Navy COAMPS (Coupled Ocean/Atmosphere Mesoscale Prediction System)

• Sigma-Z

• Atmosphere

And Ocean