Higher Resolution Operational Models

Higher Resolution Operational Models

Operational Mesoscale Model History

• Early: LFM, NGM (history)• Eta (mainly history)• MM5: Still used by some, but phasing out• NMM- Main NWS mesoscale model. Sometimes

called WRF-NMM• WRF-ARW: Heavily used by research and some

operational communities.• The NWS calls their mesoscale run NAM: North

American Mesoscale . Now NMM

Eta Model

Eta CoordinateAnd Step Mountains

MSL

ground

= 1

Ptop = 0

Horizontal resolution of 12 km

12-km terrain

Drawbacks of the Eta Coordinate

• The failure to generate downslope wind storms in regions of complex terrain

• Weak boundary layer winds over elevated terrain when compared to observations

• The displacement of precipitation maxima too far toward the bottom of steeply sloping terrain as opposed to the observed location near the top half of the terrain slope

• The reduction in the number of vertical layers used to define the model atmosphere above elevated topography particularly within the boundary layer

WRF and NMM

Why WRF?• 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

The NCEP Nonhydrostatic Mesoscale Model: NMM (Janjic et al. 2001), NWS

WRF

Hybrid sigmapressure vertical coord. 3:1 nesting ratio Conserves kinetic energy, enstrophy and

momentum using 2nd order differencing equation Modified Eta physics, Noah unified land-surface

model, NCAR physics adapted too

•The National Weather Service dropped Eta in 2006 as the NAM (North American Mesoscale) run and replaced it with WRF NMM.

•The Air Force uses WRF ARW.

•Most universities use WRF ARW

NWS NMM—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.

October 2011 Update: NMMB

• 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

18

September 2011 NAM Upgrade

Current NAM• WRF-NMM (E-grid)• 4/Day = 6 hr update• Forecasts to 84 hours• 12 km horizontal grid

spacing

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

NMM• Was generally inferior to GFS

Looks like it has improved…