Eta Model

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

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 km

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:  Terrain following hydrostatic mass (p) vertical coordinate, arbitrary vertical resolution  Arakawa C-grid, two-way nesting, any ratio  3 rd order Runge-Kutta time-split differencing  Conserves mass, entropy and scalars using up to 6 th order spatial differencing equ for fluxes (5 th order upwind diff. is default)  NCAR physics package ( converted from MM5 and Eta ), NOAH unified land-surface model, NCEP physics adapted too  Replacement for MM5

The NCEP Nonhydrostatic Mesoscale Model: NMM (Janjic et al. 2001)  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 2 nd 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 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

WRF Hierarchical Software Architecture Top-level “Driver” layer –Isolates computer architecture concerns –Manages execution over multiple nested domains –Provides top level control over parallelism patch-decomposition inter-processor communication shared-memory parallelism –Controls Input/Output “Mediation” Layer –Specific calls to parallel mechanisms Low-Level “Model” layer –Performs actual model computations –Tile-callable –Scientists insulated from parallelism –General, fully reusable Mediation Layer wrf initial_configalloc_and_configureinit_domainintegrate solve_interface solve Model Layer Driver Layer prep filter big_step decouple advance uv recouple scalars physics advance w

The National Weather Service dropped Eta ( old NAM-North American mesoscale run) in June 2006 and replace by WRF NMM (new NAM). The Air Force is now switching from MM5 to WRF ARW. Most universities using WRF ARW

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.