Eta Model

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Eta Model
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Hybrid and Eta Coordinates
Ptop
Ptop
? 0
Pressure domain
? 0
Sigma domain
? 1
MSL
? 1
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(No Transcript)
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Horizontal resolution of 12 km
12-km terrain
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WRF Model Family

• A Tale of Two Dynamical Cores

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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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Two WRF Cores

• ARW (Advanced Research WRF) (aka Mass
  Core)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 hydrostatic mass (p) vertical
  coordinate, arbitrary vertical resolution
• Arakawa C-grid, two-way nesting, any ratio
• 3rd order Runge-Kutta time-split differencing
• Conserves mass, entropy and scalars using up to
  6th order spatial differencing equ for fluxes
  (5th order upwind diff. is default)
• NCAR physics package (converted from MM5 and
  Eta), NOAH unified land-surface model, NCEP
  physics adapted too
• Replacement for MM5

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

• Hybrid sigma?pressure vertical coord.
• Arakawa E-grid, 31 nesting ratio
• Adams-Bashforth time differencing, time splitting
• Conserves kinetic energy, enstrophy and momentum
  using 2nd order differencing equation
• Separate set of equations for hydrostatic versus
  non-hydrostatic terms
• Modified Eta physics, Noah unified land-surface
  model, NCAR physics adapted too
• Parallelized within WRF infrastructure

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WRF Modeling System
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WRF Hierarchical Software Architecture

• Top-level Driver layer
• Isolates computer architecture concerns
• Manages execution over multiple nested domains
• Provides top level control over parallelism
• patch-decomposition
• inter-processor communication
• shared-memory parallelism
• Controls Input/Output
• Mediation Layer
• Specific calls to parallel mechanisms
• Low-Level Model layer
• Performs actual model computations
• Tile-callable
• Scientists insulated from parallelism
• General, fully reusable

Driver Layer
wrf
initial_
config
alloc
_and_configure
init
_domain
integrate
solve_interface
solve
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The National Weather Service dropped Eta ( old
NAM-North American mesoscale run) in June 2006
and replace by WRF NMM (new NAM). The Air Force
is now switching from MM5 to WRF ARW. Most
universities using WRF ARW
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WRF-NMM

• Same domain as Eta
• Sixty levels like Eta
• Essentially same physics as ETA
• Much better in terraindoesnt share the etas
  problems.