The Naval Research Laboratory’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS)

Abstract

The three-dimensional Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) has been developed by the Naval Research Laboratory. COAMPS consists of an atmospheric data assimilation system comprising data quality control, analysis, initialization, and nonhydrostatic forecast model components, as well as a hydrostatic ocean model. The models can be integrated simultaneously so that the surface fluxes of heat, momentum, and moisture are exchanged across the air–water interface every time step. Optionally, either the atmospheric or ocean model can be used as a stand-alone system. The atmospheric component of COAMPS was used for operational support for the America3 team in the 1995 America’s Cup races. Results of these forecasts indicated the necessity of data assimilation to reduce model spinup in the first 6 h of the forecast. Accurate forecasts of the low-level wind in the coastal race area was accomplished by utilizing triply nested grids to attain the necessary high resolution to resolve the local wind patterns and the underlying surface terrain field. Two idealized simulations of a tropical cyclone were performed with COAMPS. In the first simulation, only the atmospheric model was used, assuming a fixed sea surface temperature (SST). A realistic structure developed with spiral bands of convection present outside the inner eyewall. These spiral bands occasionally contracted inward resulting in rapid fluctuations in the intensity of the tropical cyclone. In the second simulation, the ocean model was run simultaneously with the atmospheric model. The SST cooled over 8°C over a small area within the radius of maximum winds, resulting in a much weaker system. However, there appeared to be little effect on the overall strength of the system, as measured by the tangential velocities outside the radius of maximum winds.