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Eta Model. ground. ground. Hybrid and Eta Coordinates. Ptop. Ptop.  = 0. Pressure domain.  = 0. Sigma domain.  = 1. MSL.  = 1. Horizontal resolution of 12 km. 12-km terrain. WRF Model Family. A Tale of Two Dynamical Cores. Why WRF?.

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Slide2 l.jpg

ground

ground

Hybrid and Eta Coordinates

Ptop

Ptop

 = 0

Pressure domain

 = 0

Sigma domain

 = 1

MSL

 = 1



Wrf model family l.jpg

WRF Model Family

A Tale of Two Dynamical Cores


Why wrf l.jpg
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, 3:1 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 Software Infrastructure 2001)

Dynamic Cores

Mass Core

NMM Core

Static

Initialization

Post Processors,

Verification

Obs Data,

Analyses

3DVAR Data

Assimilation

Standard Physics Interface

Physics Packages

WRF Modeling System


Wrf hierarchical software architecture l.jpg

Top-level “Driver” layer 2001)

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

Mediation Layer

uv

prep

filter

scalars

physics

big_step

recouple

decouple

advance w

advance

Model Layer

WRF Hierarchical Software Architecture

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 American mesoscale run) in June 2006 and replace by WRF NMM (new NAM).

  • Same domain as Eta

  • Sixty levels like Eta

  • Essentially same physics as ETA

  • Much better in terrain…doesn’t share the eta’s problems.


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