Characteristics of the RAW-Filtered Leapfrog Time-Stepping Scheme in the Ocean General Circulation Model

The Robert-Asselin-Williams (RAW) filtered leapfrog scheme is implemented and tested in the Taiwan multiscale community ocean model (TIMCOM). The characteristics of the RAW filter are carefully examined through two benchmark tests (the classical model problem-oscillation equation with further consideration of the dissipation effect, and the 1D linearized shallow-water equations). Particularly, the effect of the RAW filter upon the 2x wave instability due to spatial truncation errors is addressed. TIMCOM is then applied to simulate the coastally trapped internal Kelvin waves and global ocean circulations, showing the practical improvement over the Robert-Asselin (RA) filter in the short- and long-term model integrations. The large mean differences in some major current systems suggest the potential impacts on the oceanic instability where the numerical dissipation may interfere with the physical one. The characteristic analysis and model results here indicate the significant advantage of the RAW-filtered leapfrog time-stepping scheme for accurate ocean modeling.