Internal Tides in the Ocean

Speaker: Zhongxiang Zhao
Affiliation: Applied Physics Lab, University of Washington
Title: Internal Tides in the Ocean
Host: Xinfeng Liang
Abstract: Internal tides are ubiquitous in the stratified ocean and are believed to play an important role in driving ocean mixing and meridional ocean circulation. They are generated in the barotropic tide and bottom topography interaction, and transport the converted tidal energy over hundreds to thousands of km in the open ocean. Our understanding of internal tides based on field measurements is poor, mainly because field measurements are sparse in the ocean. Fortunately, great progresses have been made in observing internal tides by satellite altimetry, which detects the internal tide’s cm-scale fluctuations at the sea surface. The global maps of M2, S2, K1 and O1 internal tides are constructed by 25 years of satellite altimeter data. Their generation, long-range propagation, phase/group speeds, refraction, reflection, and convergence/divergence are examined. Internal tide energy is also estimated from its sea surface height amplitude. Mode-1 and mode-2 internal tides are separately resolved by satellite altimetry. It is suggested that internal tides can be used to monitor ocean heat content changes from small changes in their propagation speed by internal tide oceanic tomography (ITOT, similar to acoustic tomography). In the end, the global internal tide fields simulated by several numerical models are also discussed.

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