WRF Modeling System Features

NMM Dynamical Solver

The WRF-NMM is a fully compressible, non-hydrostatic mesoscale model with a hydrostatic option (Janjic et al. 2001, Janjic 2003a,b). The model uses a terrain following hybrid sigma-pressure vertical coordinate. The grid staggering is the Arakawa E-grid. The same time step is used for all terms. The dynamics conserve a number of first and second order quantities including energy and enstrophy (Janjic 1984).

The WRF-NMM model code contains an initialization program (real_nmm.exe; see Chapter 4 of the WRF-NMM User's Guide) and a numerical integration program (wrf.exe; see Chapter 5 of the WRF-NMM User's Guide). The WRF-NMM model Version 3 supports a variety of capabilities. The key features include:

  • Real-data simulations for applications ranging from meters to thousands of kilometers.
  • Fully compressible, non-hydrostatic model with a hydrostatic (runtime) option (Janjic, 2003a).
  • Hybrid (sigma-pressure) vertical coordinate.
  • Arakawa E-grid.
  • Forward-backward scheme for horizontally propagating fast waves, implicit scheme for vertically propagating sound waves, Adams-Bashforth Scheme for horizontal advection, and Crank-Nicholson scheme for vertical advection. The same time step is used for all terms.
  • Conservation of a number of first and second order quantities, including energy and enstrophy (Janjic 1984).
  • Full physics options for land-surface, planetary boundary layer, atmospheric and surface radiation, microphysics, and cumulus convection.
  • One-way and two-way nesting with multiple nests and nest levels.
  • WRF-NMM Dynamics

    Time stepping

    Horizontally propagating fast-waves: Forward-backward scheme
    Vertically propagating sound waves: Implicit scheme
    Horizontal: Adams-Bashforth scheme
    Vertical: Crank-Nicholson scheme
    TKE, water species: Explicit, iterative, flux-corrected (called every two time steps).

    Advection (space) for T, U, V

    Horizontal: Energy and enstrophy conserving, quadratic conservative, second order
    Vertical: Quadratic conservative, second order
    TKE, Water species: Upstream, flux-corrected, positive definite, conservative

    Diffusion

    Diffusion in the WRF-NMM is categorized as lateral diffusion and vertical diffusion. The vertical diffusion in the PBL and in the free atmosphere is handled by the surface layer scheme and by the boundary layer parameterization scheme (Janjic 1996a, 1996b, 2002a, 2002b). The lateral diffusion is formulated following the Smagorinsky non-linear approach (Janjic 1990). The control parameter for the lateral diffusion is the square of Smagorinsky constant.

    Divergence damping

    The horizontal component of divergence is damped (Sadourny 1975). In addition, if applied, the technique for coupling the elementary subgrids of the E grid (Janjic 1979) damps the divergent part of flow.

    Physics

    Below is a summary of physics options that are well-tested for WRF-NMM and used operationally at NCEP:

    &physics

    Identifying Number

    Physics options

    mp_physics (max_dom)

    5

    Microphysics-Ferrier

    ra_lw_physics

    99

    Long-wave radiation - GFDL

    (Fels-Schwarzkopf)

    ra_sw_physics

    99

    Short-wave radiation - GFDL (Lacis-Hansen)

    sf_sfclay_physics

    2

    Surface-layer- Janjic scheme

    sf_surface_physics

    2

    Land-surface - Noah LSM

    bl_pbl_physics

    2

    Boundary-layer - Mellor-Yamada-Janjic TKE

    cu_physics

    2

    Cumulus - Betts-Miller-Janjic scheme

    num_soil_layers

    4

    Number of soil layers in land surface model

    Below is a summary of physics options that have been tested for the WRF-NMM and whether they run or fail:

    Physics Options

    Runs (option)

    Fails (option)

    Microphysics

    WSM5 (4)

    Ferrier (5)*

    WSM6 (6)

    Thompson (8)

    Lin (2)

    WSM3 (3)

    Radiation (lw/sw)

    GFDL/GFDL (99)*

    RRTM/Dudhia (1)

    Goddard (2)

    Sfc Layer/PBL

    M-O/YSU (1)

    Janjic/MYJ (2)*

    GFS/GFS (3)

    QNSE (4)

    GFDL (88)

     

    LSM

    Unified Noah (2)*

    RUC (3)

    GFDL (88)

     

    Cummulus

    None (0)

    KF (1)

    BMJ (2)*

    GD (3)

    AS (4)*

     

    * indcates well-tested for WRF-NMM

    (For more details and references, see the Physics Options section in Chapter 5 of the WRF-NMM User's Guide.)

    Inputs for WRF initialization

    Real-data using WRF Preprocessing System (WPS) conversion from Grib files

    I/O options

    netCDF, most common. Works with all supported graphics.

    Platforms it runs on

    Below is a summary of platforms that are tested for WRF-NMM:

    Vendor

    Hardware

    O.S.

    Compiler

    Cray

    X1

    UniCOS

    vendor

    Cray

    AMD

    Linux

    PGI/PathScale

    IBM

    Power Series

    AIX

    vendor

    SGI

    IA64/Opteron

    Linux

    Intel

    COTS*

    IA32

    Linux

    Intel/PGI/gfortran/g95/PathScale

    COTS*

    IA64/Opteron

    Linux

    Intel/PGI/gfortran/PathScale

    Mac

    Power Series

    Darwin

    xlf/g95/PGI/Intel

    Mac

    Intel

    Darwin

    g95/PGI/Intel

    *Commercial off the shelf systems.

    (For more details and references, see Chapter 2 of the WRF-NMM User's Guide.)

    Software Architecture

    Hierarchical software architecture that insulates scientific code (Model Layer) from computer architecture (Driver Layer).

    Multi-level parallelism supporting shared-memory (OpenMP), distributed-memory (MPI), and hybrid share/distributed modes of execution.

    Active data registry: defines and manages model state fields, I/O, nesting, configuration, and numerous other aspects of WRF through a single file, called the Registry.

    ESMF Time Management, including exact arithmetic for fractional time steps (no drift).

    Software architecture documentation, both on-line (web based browsing tools) and in-line are available.