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., sigma-theta

Sigma

Sigma-Theta

Hybrid and Eta Coordinates

ground MSL

ground

Pressure domain

Sigma domain

= 0

= 1 = 1

Ptop Ptop = 0

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

Obs Data,Analyses

Post Processors,Verification

WRF Software Infrastructure

Dynamic Cores

Mass Core

NMM Core…

Standard Physics Interface

Physics Packages

StaticInitialization

3DVAR DataAssimilation

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 sigmapressure 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

Guam

18Z

06Z

00Z12Z

00Z12Z

06Z18Z

00Z12Z

4.0 km WRF-NMM

5.15 km WRF-ARW

48 hr fcsts from both

Unless there are hurricanes

Expanded PR/Hispaniola domain

March 2011 Upgrade of HiResWindow

Details of NCEP HiResWindow Runs No Changes with This Upgrade

WRF-NMM WRF-ARWHorizontal 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 NOAH

Radiation (SW/LW)

GFDL/GFDL Dudhia/RRTM

Parameterized Convection

None None

NMM

• Was generally inferior to GFS