日本財団 図書館


Boundary Mixing Processes by Internal Waves in the North Pacific

 

Toshiyuki Awaji*1, Tomohiro Nakamura*1, Takaki Hatayama*1, Kazunori Akitomo*1 and Takatoshi Takizawa*2

*1 Kyoto University

*2 Japan Marine Science and Technology Center

 

As an example of studies for boundary mixing processes, numerical experiments with a nonhydrostatic model are performed to investigate the vertical mixing induced by tidally generated internal waves in the Kuril Straits, which is thought to be a key factor in the formation of the North Pacific Intermediate Water (NPIW). The results show that sill-scale internal waves at the K1 tidal frequency are confined to the sill slopes because the K1 tide is subinertial in the Kuril Straits. In contrast to previous studies, we show that intense short internal waves generated at the sill breaks by the subinertial K1 tidal current can propagate upstream as the tidal current slackens. Our theoretical considerations identify these short waves as unsteady lee waves, which tend to be trapped at the generation region and grow into large-amplitude waves, eventually inducing vigorous mixing along their ray paths. In particular, supoerposition of a propagating unsteady lee wave and a newly generated lee wave over a sill causes significant wave breaking leading to a maximum vertical diffusivity of about 103 cm2s-1. This quite intense mixing reaches down to the density layer of the NPIW. In contrast, the M2 tidal current does not cause such strong vertical mixing because most of generated internal waves propagate away as 1st-mode internal tides. We therefore suggest that the observed modification of the Okhotsk Sea water required in the formation of the NPIW is caused by the generation of lee waves through interactions between the K1 current and the bottom topography of the Kuril Straits.

 

Circulation in the South China Sea

 

Su Jilan

Second Institute of oceanography, State Oceanic Administration

 

South China Sea is one of the under-studied coastal oceans of the world. However, recently there have been increasing research interests in this ocean, for example, its water exchange with the Pacific Ocean through the Bashi Channel and its interaction with the Asian monsoons. In this presentation both observational results and numerical studies of the South China Sea circulation related to these two aspects are discussed.

 

 

 

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