WRF Project Overview Joseph B. Klemp, NCAR COMET WORKSHOP Boulder, Colorado 31 March 2000

1. Weather Research and Forecasting (WRF) Model WRF Project Overview Joseph B. Klemp, NCAR COMET WORKSHOP Boulder, Colorado 31 March 2000

2. Weather Research and Forecast (WRF) Model Ü Develop an advanced mesoscale forecast and assimilation system Ü Promote closer ties between research and operations Research: Design for 1-10 km horizontal grids Advanced data assimilation and model physics Accurate and efficient across a broad range of scales Well-suited for both research and operations Community model support

3. WRF Project Collaborators • Original Partners: • NCAR Mesoscale and Microscale Meteorology Division • NOAA National Centers for Environmental Prediction • NOAA Forecast Systems Laboratory • OU Center for the Analysis and Prediction of Storms • Additional Collaborators: • Air Force Weather Agency • NOAA Geophysical Fluid Dynamics Laboratory • NASA GSFC Atmospheric Sciences Division • NOAA National Severe Storms Laboratory • NRL Marine Meteorology Division • EPA Atmospheric Modeling Division • University Community

4. WRFProject Management WRF Oversight Board WRF Coordinator WRF Science Board WRF Development Teams (5)

5. WRF Oversight Board (WOB) • Responsible for overall supervision of the WRF Project: • Monitors plans and progress of the project • Obtains commitments from the heads of participating agencies • Deals with funding requests and budget issues • Provides progress reports to the USWRP IWG and other funding agencies • Appoints the WRF Coordinator and members of the WRF Science Board • Members represent organizations that have made a major commitment of time and resources to the WRF effort • Steve Lord, chair NOAA/NCEP • Bob Gall NCAR/MMM • Steve Nelson NSF/ATM • Sandy MacDonald NOAA/FSL & GFDL • Col. Charles French USAF/AFWA

6. WRF Science Board (WSB) • Provides technical guidance to the WRF effort to help ensure that WRF will meet the needs of a broad community in both research and operations • Identifies functional requirements for desired applications • Provides feedback on technical approaches • Promotes active participation in WRF development efforts • Members represent a broad constituency of the research and operational mesoscale forecast community: • Appointed for three-year terms • Communicate via email, web postings, and annual meetings

7. WRF Coordinator Provides overall coordination of the WRF Project • Keeps the WOB informed of progress and seeks advice on issues that cannot be resolved at the working level • Appoints WRF Development Teams leaders • Works together with Team Leaders to ensure that: • Overall design goals are achieved • Milestones are accomplished on schedule • Efforts are coordinated among development teams • Technical issue and progress are discussed with the WSB

8. WRF Development Teams

9. WRF Software Objectives • Performance-Portable • Performance: scaling and time to solution • Architecture independence • No specification of external packages • Run-Time Configurable • Scenarios, domain sizes, nest configurations • Dynamical-core and physics • Maintainability & Extensibility • Single source code • Modular, hierarchical design, coding standards • Plug compatible physics, dynamical cores

10. Single version of code enabled for efficient execution on: Distributed-memory multiprocessors Shared-memory multiprocessors Distributed memory clusters of SMPs Logical domain 1 Patch, divided into multiple tiles Inter-processor communication WRF Multi-Layer Domain Decomposition • Model domains are decomposed for parallelism on two-levels • Patch: section of model domain allocated to a distributed memory node • Tile: section of a patch allocated to a shared-memory processor within a node • Distributed memory parallelism is over patches; shared memory parallelism is over tiles within patches

11. WRF Hierarchical Software Architecture • Top-level “Driver” layer isolates computer architecture concerns • Manages execution over multiple nested domains • Provides top level control over parallelism, including patch-decomposition, inter-processor communication, shared-memory parallelism, etc. • Controls Input/Output • Low-Level “Model” layer code performs actual model computations • Is written to be callable for calculations within a single tile • Allows scientists to work with clean application code • Intermediate “Mediation” layer mediates between model and driver layers • Fortran90 facilitates hierarchical architecture • Allows dynamic memory allocation, derived data-types, pointers • Streamlines grid management

12. Parallel Scaling on Compaq Computer

13. Alpha workstation (EV56) 30 25 20 15 10 5 81 41 Y tile dimension 0 21 21 41 81 X tile dimension VPP 5000 100 80 60 40 20 0 -20 -40 81 -60 41 Y tile -80 dimension 21 21 41 81 X tile dimension Penalty for IJK Loop Order • IJK versus KIJ for all patch dimensions X,Y=(21,41,81); 41 levels throughout • Penalty for IJK decreases with increased length of minor dimension, X • Penalty is most severe for sizes typical of a DM patch • IJK is strongly favored by vector for adequate length of X • Surprise: vector prefers KIJ for short X; but an unlikely result once full physics

14. Numerics for Dynamical Model Solver • Numerical Modeling Issues: • Equations / variables • Vertical coordinate • Terrain representation • Grid staggering • Time Integration scheme • Advection scheme • Strategy: • Identify and analyze alternative procedures • Evaluate alternates in idealized simulations • Evaluate in NWP applications as model complexity increases

15. Mountain Wave with Step Terrain Coordinate

16. Prototype Nonhydrostatic Model Solvers • Split-Explicit Eulerian Model: • Pressure and temperature diagnosed from thermodynamics • Two time level split-explicit time integration • Flux-form prognostic equations in terms of conserved variables • Accurate shape preserving advection • Both terrain-following height and mass coordinates being tested • Semi-Implicit Semi-Lagrangian Model: • Unstaggered (A) grid • Forward trajectories with cascade interpolation back to grid • High order compact differencing • Terrain following hybrid coordinate

17. Pressure terms directly related to : Flux-Form Equations in Height Coordinates Conservative variables: Inviscid, 2-D equations in Cartesian coordinates

18. Flux-Form Equations in Mass Coordinates Hydrostatic pressure coordinate: Conservative variables: Inviscid, 2-D equations without rotation:

19. Comparison of Height and Mass Coordinates

20. Strategy for WRF Model Physics • Implement and test basic physics in WRF: • Kessler-type (no-ice) microphysics • Lin et al. (graupel included) microphysics • Kain-Fritsch cumulus parameterization • Shortwave radiation (cloud-interactive) from MM5 • Longwave radiation (RRTM) • MRF (Hong and Pan) PBL • Blackadar surface slab ground temperature prediction • Implement a complete suite of research physics packages • Encourage and facilitate community involvement in advanced model physics development and evaluation

21. WRF 3D-Var Data-Assimilation System • Essential features of initial 3D-Var system: • Basic quality control • Assimilation of conventional observations (surface, radiosonde, aircraft) • Multivariate analysis • Adherence to WRF coding standards • Additional features to be added: • Anisotropic background errors • Additional observation operators (radar, satellite, wind profiler, etc.) • Flexible choice of first guess • Further enhancements

22. WRF Model Testing and Verification Strategy • Analytic and converged numerical solutions • Inviscid dynamics (baroclinic instability, frontogenesis) • Buoyancy driven flow (gravity currents, warm thermals) • Topographic flow (nonhydrostatic, hydrostatic, inertial-gravity mountain waves) • Moist convection (idealized convection with constant eddy mixing) • Regime dependence of nonlinear flows • Topographic flow (finite amplitude waves, wave overturning, lee vortices) • Moist convection (convective behavior as a function of CAPE and shear) • Observational case studies • Extratropical cyclones (STORM-FEST case) • Topographic flow (downslope windstorm, orographic precip., cold-air damming) • Moist convection (supercell case, squall-line case, multi-parameter radar case) • PBL-surface physics (1-D dirunal cycle, sea-breeze case, marine inversion and CTD)

23. Tentative Timeline for WRF Project

24. WRF Calendar for 2000 12 January 14 February 29-30 March 23 June First WRF Oversight Board Meeting WRF Planning Meeting WRF Planning Workshop First Annual WRF Users Workshop WRF Status & Updates: www.wrf-model.org