Nesting

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 kmeta

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

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 and replace by WRF NMM (new NAM). The Air Force is now switching from MM5 to WRF ARW. Most universities using WRF ARW

On June 13, 2006 starting with the 12 UTC model run, NCEP will replace the forecast model used in its North American Mesoscale (NAM) time slot. Currently the the Eta forecast model is used for the NAM, but on this date it will be replaced with the Non-hydrostatic Mesoscale Model (NMM) in the WRF framework The WRF/NMM with continue to run over the same domain and same horizontal resolution (12 km) as the Eta and its output will be available at the same time. Specifics on the differences between the Eta and WRF/NMM systems are as follows: 1. Model Changes - Replace Eta prediction model with WRF version of the Non-hydrostatic Meso Model (WRF-NMM) - Extended model top pressure from 25 mb to 2 mb - Replace Eta step-mountain vertical coordinate with NMM hybrid sigma-pressure vertical coordinate - Refined/retuned numerous aspects of the Eta model physics for use in the NMM - Replace Eta 3DVAR analysis system with the new unified GSI analysis system that has been adapted for application to the WRF-NMM

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.

15 UTC 19 June 12 UTC 19 June

Round One Subjective Impressions Surface and near surface wind and temperature fields are similar WRF has more intense, detailed, and more extensive precipitation structures.

Round Two Objective Verifications Both WRF and MM5 were verified against large array of surface observations over the Pacific Northwest. Model output was linearly interpolated to observation sites within the 12-km domain encompassing the Pacific Northwest. Will show statistics from 12 UTC March 29 to 12 UTC June 6, 2005

2- m Temperature Mean Absolute Error Forecast Hour oCoC 12-km domain, 12 UTC initialization, roughly 60,000 observations in each

10-m Wind Speed Mean Absolute Error kt Forecast Hour

Wind Direction Mean Absolute Error Forecast Hour Degrees

Surface Pressure Mean Absolute Error mb Forecast Hour

6-h Precipitation Mean Absolute Error inch Forecast Hour