Transformation of the Indonesian Throughflow Water by Vertical Mixing and Its Relation to Tidally Generated Internal Waves |
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Authors: | Takaki Hatayama |
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Institution: | (1) Japan Agency for Marine-Earth Science and Technology, Yokohama Institute for Earth Sciences, Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan |
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Abstract: | Numerical experiments with two-dimensional nonhydrostatic model have been performed to investigate tidally generated internal
waves at the Dewakang sill at the southern Makassar Strait where two large-amplitude “bumps” of relatively shallow water exist.
We investigate the effect of these features on vertical mixing, with emphasis on the transformation of the Indonesian throughflow
(ITF) water properties. The result shows that large-amplitude internal waves are generated at both bumps by the predominant
M2 tidal flow, even though the condition of the critical Froude number and the critical slope are not satisfied. The internal
waves induce such vigorous vertical mixing in the sill region that the vertical diffusivity attains a maximum value of 6 ×
10−3 m2s−1 and the salinity maximum and minimum core layers characterizing the ITF thermocline water are considerably weakened. Close
examination reveals that bottom-intensified currents produced mainly by the joint effect of barotropic M2 flow and internal tides generated in the concave region surrounding both bumps can excite unsteady lee waves (Nakamura et al., 2000) on the inside slopes of the bumps, which tend to be trapped at the generation region and grow into large-amplitude
waves. Such generation of unsteady lee waves does not occur in case of one bump alone. Trapping and amplification of the waves
in the sill region induce large vertical displacements (∼60 m) of water parcels during one tidal period, leading to strong
vertical mixing there. Since the K1 tidal currents are relatively weak, large-amplitude internal waves causing intense vertical mixing are not generated.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | Tidally-induced internal waves vertical mixing the Indonesian Throughflow nonhydrostatic numerical model |
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