User’s Guide for Advanced Research WRF (ARW) Modeling System Version 2

Chapter 1: Overview

Table of Contents

• Introduction
• The WRF ARW Modeling System Program Components

Introduction

The Advanced Research WRF (ARW) modeling system has been in development for the past few years. The current release is Version 2. The ARW is designed to be a flexible, state-of-the-art atmospheric simulation system that is portable and efficient on available parallel computing platforms. The ARW is suitable for use in a broad range of applications across scales ranging from meters to thousands of kilometers, including:

• Idealized simulations (e.g. LES, convection, baroclinic waves)
• Parameterization research
• Data assimilation research
• Forecast research
• Real-time NWP
• Coupled-model applications
• Teaching

The Mesoscale and Microscale Meteorology Division of NCAR is currently maintaining and supporting a subset of the overall WRF code (Version 2) that includes:

• WRF Software Framework (WSF)
• Advanced Research WRF (ARW) dynamic solver, including one-way, two-way nesting and moving nest.
• The WRF Preprocessing System (WPS)
• WRF Variational Data Assimilation (WRF-Var) system which currently supports 3DVAR capability
• Numerous physics packages contributed by WRF partners and the research community
• Several graphics programs and conversion programs for other graphics tools

And these are the subjects of this document.

Other components of the WRF system will be supported for community use in the future, depending on interest and available resources.

The WRF modeling system software is in the public domain and is freely available for community use.

The WRF Modeling System Program Components

The following figure shows the flowchart for the WRF Modeling System Version 2.

As shown in the diagram, the WRF Modeling System consists of these major programs:

• The WRF Preprocessing System (WPS)
• WRF-Var
• ARW solver
• Post-processing graphics tools

WPS

This program is used primarily for real-data simulations. Its functions include 1) defining simulation domains; 2) interpolating terrestrial data (such as terrain, landuse, and soil types) to the simulation domain; and 3) degribbing and interpolating meteorological data from another model to this simulation domain.

WRF-Var

This program is optional, but can be used to ingest observations into the interpolated analyses created by WPS. It can also be used to update WRF model's initial condition when WRF model is run in cycling mode.

ARW Solver

This is the key component of the modeling system, which is composed of several initialization programs for idealized, and real-data simulations, and the numerical integration pragram. It also includes a program to do one-way nesting. The key feature of the WRF model includes:

• fully compressible nonhydrostatic equations with hydrostatic option
• complete coriolis and curvature terms
• two-way nesting with multiple nests and nest levels
• one-way nesting
• moving nests
• mass-based terrain following coordinate (note that the height-based dynamic core is no longer supported)
• vertical grid-spacing can vary with height
• map-scale factors for conformal projections:
• polar stereographic
• Lambert-conformal
• Mercator
• Arakawa C-grid staggering
• Runge-Kutta 2nd and 3rd order timestep options
• scalar-conserving flux form for prognostic variables
• 2nd to 6th order advection options (horizontal and vertical)
• time-split small step for acoustic and gravity-wave modes:
• small step horizontally explicit, vertically implicit
• divergence damping option and vertical time off-centering
• external-mode filtering option
• lateral boundary conditions
• idealized cases: periodic, symmetric, and open radiative
• real cases: specified with relaxation zone
• full physics options for land-surface, PBL, radiation, microphysics and cumulus parameterization

Graphics Tools

Several programs are supported, including RIP4 (based on NCAR Graphics), NCAR Graphics Command Language (NCL), and conversion programs for other readily available graphics packages: GrADS and Vis5D.

The details of these programs are described more in the chapters in this user's guide.