It is recapitulated that the gravitational potential energy that is conserved along the neutral surfaces needs two terms, one from buoyancy and the other from gravity. I also show a mathematical identity for the time change of this gravitational potential energy which can be interpreted as exchange of energy amongst kinetic, internal, and gravitational potential forms. Movements along the neutral surface conserve the gravitational potential energy and it is shown that not only conversions into and out of the gravitational potential energy balance, but that each of the conversion terms is zero.

Feasibility of observing near-inertial waves with a single cast of a lowered Acoustic Doppler Current Profiler is quantitatively assessed in simulated Garrett-Munk internal waves. Because the inertial period is shorter in higher latitudes and the interval between the upand downcasts is longer in shallower depths, the performance of the estimator is better in higher latitudes at shallower depths. Even in the best conditions, however, the estimates are contaminated by relative uncertainties greater than 100%. It is not feasible to estimate nearinertial waves accurately using a LADCP cast. Nevertheless, repeated casts at one station are capable of resolving typical near-inertial waves.

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.