Oceanography Vol. 18, No. 4, Dec. 2005 62 Ocean. We used a tidal model to simulate the barotropic and baroclinic tides in the Indonesian seas to verify model perfor- mance against observations and to pro- vide examples of baroclinic tidal activity. Although internal tides have been ob- served in the Indonesian seas, the baro- clinic tidal fields are not well known. In particular, relatively few full-depth, long- period current observations suitable for accurately quantifying the baroclinic tidal fields exist. More complete coverage has been provided by modeling stud- ies; good replication of the barotropic fields has been obtained by Mazzega and Bergé (1994), Hatayama et al. (1996), and Egbert and Erofeeva (2002) us- ing two-dimensional simulations. For the baroclinic tides, three-dimensional simulation is required to include vertical variability. Schiller (2004) and Simmons et al. (2004) simulated the baroclinic tides in the Indonesian seas on coarse grids (~0.5° in latitude and longitude, or ~50 km) using a z-level model (Modular Ocean Model [MOM]) and an isopyc- nal model, respectively. However, the grid cell sizes of these simulations are inadequate to resolve the internal tides in depths less than 2000 m where the internal tidal wavelength ranges from ~20–50 km. Grid cells of 4–5 km or finer are required to resolve the internal wavelengths in shallow water (Holloway, 2001). In a study for Fieberling Guyot (Robertson, submitted), a resolution of 1 km was required to accurately predict mean currents and major axis ampli- tudes. In the Fieberling Guyot study, model performance improved with high- er-resolution (< 1 km) bathymetry and more vertical layers; however, a resolu- tion of ~5 km was sufficient for indicat- ing where baroclinic tides occur. In this study, our goal is to estimate the baroclinic tidal fields for the Indo- nesian seas to provide baroclinic tidal information for future observational programs and focused regional modeling studies. Computing limitations require a balance between geographic coverage and model performance, which is reso- lution dependent. For our overview, we selected a resolution of 5 km in order to include the entire Indonesian seas re- gion, realizing that this would be a more qualitative estimate than an accurate quantitative estimate. THE INDONESIAN SEAS BY ROBIN ROBERTSON AND AMY FFIELD seas (Munk and Wunsch, 1998; Garrett, 2003). In a stratified ocean, when the ver- tically uniform horizontal velocities of barotropic tides (tides in which surfaces of constant pressure are parallel to sur- faces of constant density) interact with rough topography, disturbing isotherms and isopycnals, they generate baroclinic tides, for which the velocities are not ver- tically uniform. Currents, internal waves, and heaving isotherms resulting from baroclinic tides affect forces on structures and vessels. Vigorous internal tides have been observed in the Indonesian seas with isotherm excursions up to 90 m in the Ceram Sea during 14-hour yo-yo sta- tions (Ffield and Gordon, 1996). Tides also affect the generation of mean cur- rents and mixing. Mixing processes mod- ify the ocean’s hydrography, or physical characteristics, leading to density-driven flows. In the Indonesian seas, mixing transforms the Pacific inflow waters into Indonesian throughflow waters (Gordon, this issue) before export to the Indian Baroclinic, or internal, tides play a significant role in mixing in the deep ocean and in shallow M 2 BAROCLINIC TIDES in the Indonesian Seas Tis article has been published in Oceanography, Volume 18, Number 4, a quarterly journal of Te Oceanography Society. Copyright 2005 by Te Oceanography Society. All rights reserved. Permission is granted to copy this article for use in teaching and research. Republication, systemmatic reproduction, or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of Te Oceanography Society. Send all correspondence to: info@tos.org or T e Oceanography Society, PO Box 1931, Rockville, MD 20849-1931, USA.