A Framework for Coupled Modeling

A coupling framework has been built to provide a streamlined, flexible, and efficient modeling environment in which to couple models, such as atmosphere, ocean, and wave models. The coupling framework does not require any changes to any of the model's structures, and only minimum code and script changes are required for each model. Under this framework, separate executables are used for each model, and the models exchange information during the simulation. Namelist and environment variables are used to control the exchange frequency between the different coupled models. Actions taken by each model component (such as write, read, and wait) are based on the clock time and scheduled actions that need to take place at a specified time.

The Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPSŪ¹), the NRL Coastal Ocean Model (NCOM), and Wave Watch III (WW3) have been coupled successfully under this framework and have been tested for Hurricane Frances (2004). The coupler has been created to control all the data transfer between the different models. Since configurations (grid resolution, number of domains and their locations) for each model can be different, the coupling framework collects the model configuration of each model and transfers data from one model to another model based on domain resolution and location (including moving nests). One-way and two-way coupled COAMPS-NCOM, and one-way coupled COAMPS-WW3 forecasts have been performed using this framework. Results show that the coupling framework adds less than 3% overhead to the cost of running the systems.

¹COAMPSŪ is a registered trademark of the Naval Research Laboratory.