1. Higher Resolution Operational Models

2. 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

3. Vertical Coordinate Systems
Originally p and z
Then eta, sigma p and sigma z, theta
Increasingly use of hybrids– e.g., sigma-theta

4. Sigma

5. Sigma-Theta

6. Hybrid and Eta Coordinates
Ptop
Ptop
 = 0
Pressure domain
 = 0
Sigma domain
ground
 = 1
ground
 = 1
MSL

7. Horizontal resolution of 12 km
12-km terrain

8. Nesting

9. 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.

12. A Tale of Two Dynamical Cores
WRF Model Family
A Tale of Two Dynamical Cores

13. 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

14. Standard Physics Interface
WRF Modeling System
Obs Data,
Analyses
Post Processors,
Verification
WRF Software Infrastructure
Dynamic Cores
Mass Core
NMM Core …
Standard Physics Interface
Physics Packages
Static
Initialization
3DVAR Data
Assimilation

15. 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

16. 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

17. The NCEP Nonhydrostatic Mesoscale Model: NMM (Janjic et al
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

18. 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

19. 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.

20. NAM 12-km Domain (dashed)

21. In March Added 4-km Domains

22. March 2011 Upgrade of HiResWindow
4.0 km WRF-NMM
5.15 km WRF-ARW
48 hr fcsts from both
Unless there are hurricanes
18Z
Expanded PR/Hispaniola domain
00Z
12Z
00Z
12Z
00Z
12Z
Guam
06Z
06Z
18Z

23. 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 sigma-pressure hybrid
35 sigma
PBL/turbulence
MYJ
YSU
Microphysics
Ferrier
WSM3
Land-Surface
NOAH
Radiation (SW/LW)
GFDL/GFDL
Dudhia/RRTM
Parameterized Convection
None

24. NMM
Was generally inferior to GFS