Transcript WRFdetail.ppt

Nesting
Eta Model
Hybrid and Eta Coordinates
Ptop
Ptop
=
0
Pressure domain
=
0
Sigma domain
ground
ground
=1
MSL
=1
Horizontal resolution of 12 km
12-km terrain
WRF Model Family
A Tale of Two Dynamical Cores
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 kmeta
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
The NCAR ARW Core Model:
(See: www.wrf-model.org)
 Terrain following hydrostatic mass (p) vertical
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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
The NCEP Nonhydrostatic Mesoscale
Model: NMM (Janjic et al. 2001)
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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
WRF Modeling System
WRF Software Infrastructure
Obs Data,
Analyses
Static
Initialization
3DVAR Data
Assimilation
Dynamic Cores
Mass Core
NMM Core
…
Standard Physics Interface
Physics Packages
Post Processors,
Verification
WRF Hierarchical Software Architecture
• Top-level “Driver” layer
– Isolates computer architecture concerns
– Manages execution over multiple nested
domains
– Provides top level control over parallelism
Driver Layer
• patch-decomposition
• inter-processor communication
• shared-memory parallelism
initial_config
– Controls Input/Output
wrf
alloc_and_configure
Mediation Layer
Model Layer
Performs actual model computations
Tile-callable
Scientists insulated from parallelism
General, fully reusable
filter
physics
scalars
recouple
advance uv
decouple
advance w
solve
– Specific calls to parallel mechanisms
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–
integrate
solve_interface
• “Mediation” Layer
• Low-Level “Model” layer
init_domain
The National Weather Service dropped Eta ( old
NAM-North American mesoscale run) in June and
replace by WRF NMM (new NAM).
The Air Force is now switching from MM5 to WRF
ARW.
Most universities using WRF ARW
On June 13, 2006 starting with the 12 UTC model run, NCEP will replace the
forecast model used in its North American Mesoscale (NAM) time slot. Currently the
the Eta forecast model is used for the NAM, but on this date it will be replaced with
the Non-hydrostatic Mesoscale Model (NMM) in the WRF framework
The WRF/NMM with continue to run over the same domain and same horizontal
resolution (12 km) as the Eta and its output will be available at the same time.
Specifics on the differences between the Eta and WRF/NMM systems are as follows:
1. Model Changes
- Replace Eta prediction model with WRF version of the Non-hydrostatic Meso
Model (WRF-NMM)
- Extended model top pressure from 25 mb to 2 mb
- Replace Eta step-mountain vertical coordinate with NMM hybrid sigma-pressure
vertical coordinate
- Refined/retuned numerous aspects of the Eta model physics for use in the NMM
- Replace Eta 3DVAR analysis system with the new unified GSI analysis system
that has been adapted for application to the WRF-NMM
WRF-NMM
•Same domain as Eta
•Sixty levels like Eta
•Essentially same physics as ETA
•Much better in terrain…doesn’t share
the eta’s problems.
12 UTC 19 June
15 UTC 19 June
Round One
Subjective
Impressions
• Surface and near surface wind and
temperature fields are similar
• WRF has more intense, detailed, and
more extensive precipitation
structures.
Round Two
Objective Verifications
• Both WRF and MM5 were verified against
large array of surface observations over the
Pacific Northwest.
• Model output was linearly interpolated to
observation sites within the 12-km domain
encompassing the Pacific Northwest.
• Will show statistics from 12 UTC March 29
to 12 UTC June 6, 2005
2- m Temperature
Mean Absolute Error
2.5
2
1.5
MM5
WRF
oC
1
0.5
0
6
12
18
24
Forecast Hour
12-km domain, 12 UTC initialization, roughly 60,000 observations in each
10-m Wind Speed
Mean Absolute Error
4.5
4
3.5
3
kt 2.5
MM5
WRF
2
1.5
1
0.5
0
6
12
18
Forecast Hour
24
Wind Direction
Mean Absolute Error
70
60
50
Degrees
40
MM5
WRF
30
20
10
0
6
12
18
Forecast Hour
24
Surface Pressure
Mean Absolute Error
1.2
1
mb
0.8
MM5
WRF
0.6
0.4
0.2
0
6
12
18
Forecast Hour
24
6-h Precipitation
Mean Absolute Error
0.035
0.03
0.025
inch
0.02
MM5
WRF
0.015
0.01
0.005
0
6
12
18
Forecast Hour
24