Higher Resolution Operational Models

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Higher Resolution Operational Models
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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

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Eta Model
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Ptop
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Eta Coordinate And Step Mountains
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MSL
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Horizontal resolution of 12 km
12-km terrain
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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

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WRF and NMM
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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

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WRF Modeling System
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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
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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

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

• Hybrid sigma?pressure vertical coord.
• 31 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

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• 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

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NWS NMMThe 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.

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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

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September 2011 NAM 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
  FireWeather/IMET/DHS run to 36hr

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

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NMMB 4-km Conus
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NMM

• Was generally inferior to GFS

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Looks like it has improved
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