The Advanced Regional
Prediction System

ARPS 4.0 Characteristics

• Equations - Nonhydrostatic and fully compressible.
  
  
• Coordinate System - Generalized terrain-following coordinate with equal-spacing in x and y directions and grid stretching in the vertical. Map projection factor is included the pre-processing and post-processing programs but is NOT yet included in the dynamic equations.
• Geometry - 1-D, 2-D, 3-D configurations.
  
  
• Prognostic Variables - Cartesian windcomponents, perturbation potential temperature and pressure, subgrid-scale turbulent kinetic energy, mixing ratios for water vapor, cloud water, rainwater, cloud ice, snow and graupel/hail.
  
  
• Spatial Discretization - Second-order quadratically-conservative and fourth-order quadratically-conservative finite differences for advection, and second-order differencing for other terms. Arakawa C-grid is used.
  
  
• Temporal Discretization - Second-order leapfrog scheme for large time steps with Asselin time filter option. First-order forward-backward explicit with second-order centered implicit option for small time steps.
  
  
• Solution Technique - Split-explicit (mode-splitting) with vertically-implicit option.
  
  
• Initial State - Horizontally-homogeneous initialization using a single sounding, using analytic functions, or using three dimensional horizontally inhomogeneous data.
  
  
• Lateral Boundary Conditions - Options for periodic, rigid, zero-gradient, wave-radiating, externally-forced, and user-specified conditions.
  
  
• Top & Bottom Boundary Conditions - Options for rigid, zero-gradient, periodic, and top radiation condition using a Rayleigh sponge layer.
  
  
• Divergence Damping - The model provides an option for divergence damping to control acoustic oscillations.
  
  
• Reference Frame Rotation - Options for various Coriolis formulations.
  
  
• Domain Translation - Options for user-specified or automated (based on feature-tracking algorithms) translation of the computational domain.
  
  
• Nesting - Adaptive grid refinement interface for unlimited level of grid nesting at arbitrary locations and orientations to be placed at run time. One-way interactive self-nesting is also available.
  
  
• Subgrid Scale Turbulence - Options include Smagorinsky-Lilly diagnostic first-order closure, 1.5-order turbulent kinetic energy formulation, and Germano dynamic closure. The model also provides options for isotropic and anisotropic turbulence treatments.
  
  
• Spatial Computational Mixing - 2nd- and 4th-order options.
  
  
• Cloud Microphysics - Kessler warm-rain and 3-category ice (adapted from the NASA Goddard Cumulus Ensemble Model written by Dr. W.-K. Tao) microphysics parameterizations.
  
  
• Cumulus Parameterization - Kuo cumulus parameterization. Kain-Fritsch cumulus parameterization scheme to be added.
  
  
• Surface Layer Parameterizations - Surface momentum, heat, and moisture fluxes from bulk aerodynamic drag laws as well as stability-dependent formulations.
  
  
• Soil Model - Two-layer diffusive soil model with surface energy budget equations.
  
  
• Longwave and Shortware Radiation - A component that is related to the surface energy budget is included. Direct radiation interaction with the cloudy atmosphere to be added.
  
  
• Surface Data* - USDA surface characteristics database and pre-processing software.
  
  
• Terrain - Terrain database and pre-processing software with 30 sec terrain for most of the US and 1 deg terrain for the world.
  
  
• Objective Analysis* - Oklahoma Local Analysis and Prediction System (OLAPS) that can provide real-time analyses for model initialization.
  
  
• Interface* - Interface with NMC RUC model or Eta model is available.
  
  
• Data Assimilation - Forward-variational four-dimensional data assimilation system, augmented by a single-Doppler velocity retrieval package. These systems may be used with ARPS or as stand-alone software.
  
  
• ARPS Adjoint* - The adjoint of the dry version of ARPS 4.0 has been completed.
  
  
• History Data - ARPS supports the following history data dump formats: unformatted binary, formatted ASCII, packed binary, NCSA HDF, NetCDF, packed NetCDF, GrADS, and Savi3D (for visualization using the Savi3D software package). GRIB format will be available at a later time. These formats can be read by post-processing programs provided with the model (see below), or by user-created programs based on a template provided.
  
  
• Restart Option - Full restart capability at intervals selected by the user.
  
  
• ZXPLOT* - A vector graphics package, similar to NCAR Graphics, that performs a variety of graphics functions and supports X-windows, GKS, and postscript functionality. This package, which is the underpinning for ARPSPLT (see below), was developed by CAPS senior research scientist Dr.Ming Xue during his doctoral work at Reading University. The ZXPLOT object code (only) is currently available free of charge and is required for using ARPSPLT (see below).
  
  
• ARPSPLT* - A vector graphics post-processing package that allows the user to make contour plots, 3-D wire frame plots, and profiles of basic and derived fields using model-generated history data. The package supports overlays, color filling, user-specified contour intervals and annotation, and multiple picture formats. This package is based on ZXPLOT (see above).
  
  
• ARPSTools* - A combination of software packages supplied by both local and external users for use in analyzing output from ARPS. Capabilities include time-dependent trajectories, skew-T/log-P and hodographs, and various statistics.
  
  
• Validation - A suite of validation tests is available. These range from basic advection and symmetry tests to 3-D storm simulations. A real data test case will be available later.
  
  
• User Interfaces - ARPS and ARPSPLT utilize namelist input files which can be edited manually or configured using an X-windows interface that is particularly helpful to new users.
  
  
• Compilation - The compilations of all programs are handled by a single Unix shell script that invokes the Unix make command. The system dependencies are automatically handled by the script.
  
  
• Execution Mode - Interactive (via X-windows interface) and batch execution are supported for ARPS and ARPSPLT.
  
  
• PVM version of ARPS together with automatic parallel code translation tools.

• Oklahoma local analysis and prediction system(OLAPS);
• Adaptive grid refinement capability;
• Germano subgrid scale turbulence closure scheme;
• Forward variational data assimilation system;
• Doppler radar retrieval packages;
• Adjoint of ARPS;
• ZXPLOT library object code;
• X-window interface for ARPS and ARPSPLT;
• ARPStools.

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