Transcript WRF Model Family

Higher Resolution Operational
Models
Operational Mesoscale Model
History
•
•
•
•
•
Early: LFM, NGM (history)
Eta (mainly history)
MM5: Still used by some, but phasing out
NMM- Main NWS mesoscale model
WRF-ARW: Heavily used by research and
some operational communities.
• The NWS calls their mesoscale run NAM:
North American Mesoscale . Now NMM
Vertical Coordinate Systems
• Originally p and z
• Then eta, sigma p and sigma z, theta
• Increasingly use of hybrids– e.g., sigmatheta
Sigma
Sigma-Theta
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
Nesting
Why Nesting?
• Could run a model over the whole globe,
but that would require large amounts of
computational resource, particularly if done
at high resolution.
• Alternative is to only use high resolution
where you need it…nesting is one approach.
• In nesting, a small higher resolution domain
is embedded with a larger, lower-resolution
domain.
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 km
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
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
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
The NCEP Nonhydrostatic Mesoscale
Model: NMM (Janjic et al. 2001), NWS
WRF

Hybrid sigmapressure vertical coord.
 3:1 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
•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
NWS NMM—The 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.
NAM 12-km Domain (dashed)
In March Added 4-km Domains
March 2011 Upgrade of HiResWindow
4.0 km WRF-NMM
5.15 km WRF-ARW
18Z
48 hr fcsts from both
Unless there are hurricanes
00Z
12Z Guam
00Z
12Z
06Z
00Z
12Z
Expanded
PR/Hispaniola
domain
06Z
18Z
Details of NCEP HiResWindow Runs No
Changes with This Upgrade
WRF-NMM WRF-ARW
Horizontal grid
spacing (km)
4.0
5.15
Vertical levels
35 sigmapressure hybrid
35 sigma
MYJ
YSU
Microphysics
Ferrier
WSM3
Land-Surface
NOAH
NOAH
GFDL/GFDL
Dudhia/RRTM
None
None
PBL/turbulence
Radiation
(SW/LW)
Parameterized
Convection
NMM
• Was generally inferior to GFS