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Eta Model

Eta Model. ground. ground. Hybrid and Eta Coordinates. Ptop. Ptop.  = 0. Pressure domain.  = 0. Sigma domain.  = 1. MSL.  = 1. Horizontal resolution of 12 km. 12-km terrain. WRF Model Family. A Tale of Two Dynamical Cores. Why WRF?.

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Eta Model

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  1. Eta Model

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

  3. Horizontal resolution of 12 km 12-km terrain

  4. WRF Model Family A Tale of Two Dynamical Cores

  5. 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

  6. 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

  7. The NCAR ARW Core Model: (See: www.wrf-model.org) • Terrain following hydrostatic mass (p) vertical coordinate, arbitrary vertical resolution • Arakawa C-grid, two-way nesting, any ratio • 3rd order Runge-Kutta time-split differencing • Conserves mass, entropy and scalars using up to 6th order spatial differencing equ for fluxes (5th 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

  8. 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 2nd 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

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

  10. 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 uv prep filter scalars physics big_step recouple decouple advance w advance Model Layer WRF Hierarchical Software Architecture Driver Layer wrf initial_ config alloc _and_configure init _domain integrate solve_interface solve

  11. 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

  12. 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.

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