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 Ptop Ptop  = 0 Pressure domain  = 0 Sigma domain ground  = 1 ground  = 1 MSL

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.

A Tale of Two Dynamical Cores 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

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

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 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 48 hr fcsts from both Unless there are hurricanes 18Z Expanded PR/Hispaniola domain 00Z 12Z 00Z 12Z 00Z 12Z Guam 06Z 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 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

NMM Was generally inferior to GFS