Weather Research and Forecast (WRF) Model
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04/19/23
Weather Research and Forecast (WRF) Model
Promote closer ties between research and operations
Develop an advanced mesoscale forecast and assimilation system
Research:
Design for 1-10 km horizontal grids
Advanced data assimilation and model physics
Accurate and efficient across a broad range of scales
Well-suited for both research and operations
Community model support
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04/19/23
Original Partners:
– NCAR Mesoscale and Microscale Meteorology Division– NOAA National Centers for Environmental Prediction– NOAA Forecast Systems Laboratory– OU Center for the Analysis and Prediction of Storms
Additional Collaborators:
– Air Force Weather Agency– NOAA Geophysical Fluid Dynamics Laboratory– NASA GSFC Atmospheric Sciences Division– NOAA National Severe Storms Laboratory– NRL Marine Meteorology Division– EPA Atmospheric Modeling Division– University Community
WRF Project Collaborators
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04/19/23
WRF Project Management
WRF OversightBoard
WRF ScienceBoard
WRF Coordinator
WRF Development Teams (5)
Steve Lord, Chair NOAA/NCEPSandy MacDonald FSL &GFDLBob Gall NCAR/MMMSteve Nelson NSF/ATMCol. Charles French USAF/AFWA
Joe Klemp NCAR/MMM
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04/19/23
Numerics and Software
(J. Klemp)
Data Assimilation (T. Schlatter)
Analysis and Validation
(K. Droegemeier)
Community Involvement
(W. Kuo)
Operational Implementation
(G. DiMego)
Data Handling and Archive (G. DiMego)
NCEP Requirements
(G. DiMego)
AFWA Requirements
(M. Farrar)
Model Physics (J. Brown)
Atmospheric Chemistry (P. Hess)
Workshops, Distribution, and Support
(J. Dudhia)
Dynamic Model Numerics
(W. Skamarock)
Analysis and Visualization (L. Wicker)
Wor
king
Gro
ups
Model Testing and Verification
(C. Davis)
Software Architecture,
Standards, and Implementation (J. Michalakes)
Standard Initialization (J. McGinley)
3-D Var (J. Purser)
4-D Var,Ensemble
Techniques (D. Barker)
WRF Development Teams
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Performance-Portable
– Performance: scaling and time to solution– Architecture independence
– No specification of external packages
Run-Time Configurable– Scenarios, domain sizes, nest configurations– Dynamical-core and physics
Maintainability & Extensibility– Single source code– Modular, hierarchical design, coding standards– Plug compatible physics, dynamical cores
WRF Software Objectives
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04/19/23
Model domains are decomposed for parallelism on two-levels
– Patch: section of model domain allocated to a distributed memory node– Tile: section of a patch allocated to a shared-memory processor within a node– Distributed memory parallelism is over patches; shared memory parallelism is over tiles within
patches
Single version of code enabled for efficient execution on:
– Distributed-memory multiprocessors
– Shared-memory multiprocessors– Distributed memory clusters of
SMPs
WRF Multi-Layer Domain Decomposition
Logical domain
1 Patch, divided into multiple tiles
Inter-processor communication
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04/19/23
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
Mediation Layer
wrf
initial_config alloc_and_configure init_domain integrate
solve_interface
solve
Model Layer
Driver Layer
prep
filt
er
big_
step
deco
uple
adva
nce u
v
reco
uple
scal
ars
phys
ics
adva
nce
w
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04/19/23
Parallel Scaling on Compaq Computer
Compaq ES40, 41x81x81
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35
processors
spee
du
p
1 (2d)
2 (2d)
4 (2d)
1 (1d)
2 (1d)
4 (1d)
ideal
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04/19/23
Penalty for IJK Loop Order
IJK versus KIJ for all patch dimensions X,Y=(21,41,81); 41 levels throughout Penalty for IJK decreases with increased length of minor dimension, X Penalty is most severe for sizes typical of a DM patch IJK is strongly favored by vector for adequate length of X Surprise: vector prefers KIJ for short X; but an unlikely result once full physics
2141
81
21
41
81
0
5
10
15
20
25
30
X tile dimension
Y tile dimension
Alpha workstation (EV56)
2141
81
21
41
81
-80
-60
-40
-20
0
20
40
60
80
100
X tile dimension
Y tiledimension
VPP 5000
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04/19/23
Numerical Modeling Issues:
– Equations / variables – Vertical coordinate– Terrain representation– Grid staggering– Time Integration scheme– Advection scheme
Strategy
– Identify and analyze alternative procedures– Evaluate alternates in idealized simulations– Evaluate in NWP applications as model complexity increases
Numerics for Dynamical Solver
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04/19/23
Smooth topography well represented
Selective resolution enhancement near ground
Potential for spurious circulations above steep terrain
Can represent blocking due to step terrain
Reduced errors in computing horizontal gradients
Degraded representation of sloped topography
Maintains horizontal coordinate surfaces
Represents terrain slope accurately
Potential complications in numerics for shaved cells
Shaved Cell
Step Mountain
Terrain Following
Treatment of Terrain by Vertical Coordinate
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04/19/23
Mountain Wave with Step Terrain Coordinate
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04/19/23
Mountain Wave with Step Terrain Coordinate
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04/19/23
Split-Explicit Eulerian Model:
– Pressure and temperature diagnosed from thermodynamics– Two time level split-explicit time integration– Flux-form prognostic equations in terms of conserved variables – Accurate shape preserving advection– Both terrain-following height and mass coordinates being tested
Semi-Implicit Semi-Lagrangian Model:
– Unstaggered (A) grid– Forward trajectories with cascade interpolation back to grid– High order compact differencing– Terrain following hybrid coordinate
Prototype Nonhydrostatic Model Solvers
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04/19/23
0
z
W
x
U
t
Qz
W
x
U
t
z
Ww
x
Uwg
zR
t
W
z
Wu
x
UufV
xR
t
U
,,, wWvVuU
pcR p
Conservative variables:
Inviscid, 2-Dequations inCartesiancoordinates
Pressure termsdirectly related to
Flux-Form Equations in Height Coordinates
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04/19/23
Flux-Form Equations in Mass Coordinates
0
,,
0
p
Rpgw
dt
d
x
U
t
Qx
U
t
w
x
Uwpg
t
W
u
x
Uu
x
p
x
p
t
U
tst ,/Hydrostatic pressure coordinate:
Inviscid, 2-Dequations without rotation:
,,, wWuUConservative variables:
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04/19/23
2-D Mountain Wave Simulation
a = 1 km, dx = 200 m a = 100 km, dx = 20 km
Mass CoordinateHeight Coordinate
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04/19/23
5 min 10 min 15 min
Comparison of Gravity Current Simulations
HeightCoordinate
MassCoordinate
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Comparison of Height and Mass Coordinates
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04/19/23
Time-Split Leapfrog and Runge-Kutta Integration Schemes
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04/19/23
Define “plug-compatible” interface for physics modules
Implement and test basic physics in WRF:– Kessler-type (no-ice) microphysics – Lin et al. (graupel included) microphysics – Kain-Fritsch cumulus parameterization – Shortwave radiation (cloud-interactive) from MM5 – Longwave radiation (RRTM) – MRF (Hong and Pan) PBL – Blackadar surface slab ground temperature prediction
Implement a complete suite of research physics packages
Encourage and facilitate community involvement in advanced model physics development and evaluation
Strategy for WRF Model Physics
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04/19/23
Essential features of initial 3D-Var system:
– Basic quality control
– Assimilation of conventional observations (surface, radiosonde, aircraft)
– Multivariate analysis
– Adherence to WRF coding standards
Additional features to be added:
– 3-D anisotropic background errors using recursive filters
– Additional observation operators (radar, satellite, wind profiler, etc.)
– Flexible choice of first guess
– Further enhancements
WRF 3D-Var Data-Assimilation System
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04/19/23
WRF Model Testing and Verification Strategy
Analytic and converged numerical solutions
– Inviscid dynamics (baroclinic instability, frontogenesis)– Buoyancy driven flow (gravity currents, warm thermals)– Topographic flow (nonhydrostatic, hydrostatic, inertial-gravity mountain waves)– Moist convection (idealized convection with constant eddy mixing)
Regime dependence of nonlinear flows
– Topographic flow (finite amplitude waves, wave overturning, lee vortices)– Moist convection (convective behavior as a function of CAPE and shear)
Observational case studies
– Extratropical cyclones (STORM-FEST case)– Topographic flow (downslope windstorm, orographic precip., cold-air damming)– Moist convection (supercell case, squall-line case, multi-parameter radar case)– PBL-surface physics (1-D diurnal cycle, sea-breeze case, marine inversion and CTD)– Tropical cyclone (COMPARE case)
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04/19/23
Development Task 2000 2001 2002 2003 2004 2005-08
Basic WRF model (limited physics, standard initialization)
Research quality NWP version of WRF
Model physicsSimple Research suite Advanced
3D-Var assimilation systemBasic Research Advanced
4D-Var assimilation system, ensemble techniques
Basic Advanced
Testing for operational use at NCEP, FSL, & AFWA
Diagnosis of operational performance, refinements
Release and support to community Operational deployment
Projected Timeline for WRF Project
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04/19/23
12 January
14 February
29-30 March
23 June
30 September
First WRF Oversight Board Meeting
WRF Planning Meeting
WRF Planning Workshop
First Annual WRF Users Workshop
Release of “bare-bones” WRF Model
WRF Calendar for 2000
WRF Status & Updates: wrf-model.org