ARPS Model System Overview

In 1989, the Center for Analysis and Prediction of Storms was established at the University of Oklahoma as one of the National Science Foundation's first 11 Science and Technology (S&T) Centers. Its formal mission is to demonstrate the practicability of storm-scale numerical weather prediction and to develop, test, and validate a regional forecast system appropriate for operational, commercial, and research applications. Its ultimate vision is to make available a fully functioning stormscale NWP system around the turn of the century.

Central to achieving this goal is an entirely new three-dimensional, nonhydrostatic model system known as the Advanced Regional Prediction System (ARPS). It is a entirely new and complete numerical prediction system designed for the explicit representation of convective and cold-season storms. It includes a data ingest, quality control, and objective analysis package known as ADAS (ARPS Data Analysis System), a single-Doppler radar parameter retrieval and assimilation system known as ARPSDAS (ARPS Data Assimilation System, of which ADAS is a component), the prediction model itself, which is the topic of this paper, and a post-processing package known as ARPSPLT. These components are illustrated in the following figure.

In planning for its development, the ARPS was required to meet a number of criteria. First, it had to accommodate, through various assimilation strategies, new data of higher temporal and spatial density (e.g., WSR-88D data) than had traditionally been available. Second, the model had to serve as an effective tool for studying the dynamics and predictability of storm-scale weather in both idealized and more realistic settings. It must also handle atmospheric phenomena ranging from regional scales down to micro-scales as interactions across this spectrum are known to have profoundly important impacts on storm-scale phenomena. These needs required that the model have a flexible and general dynamic framework and include comprehensive physical processes. The system should also run efficiently on massively parallel computers. In short, it was our goal to develop a model system that can be used effectively for both basic atmospheric research and operational numerical weather prediction, on scales ranging from regional to micro-scales.

The numerical forecast component of the ARPS is a three-dimensional, nonhydrostatic compressible model in generalized terrain-following coordinates that has been designed to run on a variety of computing platforms ranging from single-processor scalar workstations to massively parallel scalar and scalar-vector processors. This highly modular code is extensively documented and has been written using a consistent style throughout to promote ease of learning and modifications well as maintainability. The present version contains a comprehensive physics package and has been applied successfully during the past few years to real-time operational prediction of storm-scale weather over the Southern Great Plains of the United States.

Principal elements of the Advanced Regional Prediction System (ARPS)

 

Current Features and Capabilities of ARPS

After almost six years of development and testing, the ARPS model now contains physics and numerical solution options consistent with most other non-hydrostatic codes. It does, however, offer a number of unique capabilities in documentation, code structure, scalability on parallel platforms, and ease of use, and thus we summarize below the current features of the system and highlight with underlining those which, in our judgement, are unique to the ARPS. Specific accomplishments for 1997 are shown in italics.

Recently Added Features and Improvement in ARPS

1997 Annual Report and 1996 Annual Report contains more detailed information on CAPS and ARPS.