Katsuro Katsumata

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Observations and simulations have shown a coastally trapped current along the Australia North West Shelf, the Holloway Current. Using output from an ocean general circulation model with parameterized tidal mixing, we investigate the seasonal variation and driving mechanism of the Holloway Current. A budget analysis shows that in 2008 the current flows southwestward from March to October, is almost stagnant in November, and flows northeastward in January and February. At seasonal times scales, the Holloway Current is generally geostrophic. The pressure field is formed in summer, by a large scale pressure field augmented with the passage of coastally trapped waves from the Gulf of Carpentaria; in autumn, by the passage of the coastally trapped wave from the Gulf; and in winter/spring, by the large scale distribution of sea surface height. The acceleration mechanisms of the Holloway Current are in summer, the long-shore wind stress and the Coriolis force; in autumn/winter, the long-shore wind stress and the Coriolis force by the offshore current; and in spring, the pressure field working against the wind stress. The heat budget shows the near-shore high pressure in autumn is a result of water convergence after the passage of the coastally trapped wave with a secondary contribution from local atmospheric heating. Although the seasonal time scale is emphasized, the variation of the flow is strongest at daily to weekly time scales. The seasonal variability is a combination of seasonally varying large scale pressure field and the residual of these synoptic daily variability such as cyclones.