Abstract
AbstractNear‐inertial internal waves (NIWs) in the abyssal Yamato and Tsushima Basins of the Japan Sea (East Sea) were investigated using data from a moored acoustic Doppler current profiler (ADCP) and single‐point current meters. The NIW events with duration of 3–5 days were observed intermittently in both basins. In particular, an active NIW event occurred below 2,475 m in the Yamato Basin during May 12–16, 2014. This was followed by the upward propagation of a wave packet from 2,475 to 950 m. The near‐inertial flows (1.07f) during the event exhibited a vertically coherent phase and intensification with depth by a factor of 1.5 from 2,475 to 2,635 m. The near‐inertial flows (1.05f) in the Tsushima Basin also showed a vertically coherent phase and intensification with depth, although the amplitude of the flow exhibited a middepth maximum rather than monotonic intensification. As a possible explanation of the observed flow characteristics, the superposition of downward‐propagating NIWs that can be excited by a strong wind event and upward‐propagating NIWs that bounced off the seabed was examined. The time series of the Richardson number based on the observed shear showed sporadic unstable conditions during the initial stage of the NIW event during May 2014 in the Yamato Basin. In addition, relatively small values of Richardson number were observed over the range of 2,475–2,635 m during the period of active NIWs. This suggests the promotion of vertical mixing in the deep sea during significant NIW events.
Highlights
Vertical mixing in the deep sea is essential for maintaining the global thermohaline circulation because cold, deep water originating from a high-latitude region acquires buoyancy via the vertical diffusion of heat from the upper layer during circulation
The near-inertial flows with the characteristics of a vertically coherent phase and varying amplitude with depth were observed in all the Near-inertial internal waves (NIWs) events
These flow characteristics can be explained by the superposition of upwardand downward-propagating NIWs
Summary
Vertical mixing in the deep sea is essential for maintaining the global thermohaline circulation because cold, deep water originating from a high-latitude region acquires buoyancy via the vertical diffusion of heat from the upper layer during circulation. Active areas of vertical mixing have been reported in various regions worldwide, such as the Izu-Ogasawara and Hawaiian Ridges in the North Pacific (Niwa & Hibiya, 2001), and Mid-Atlantic Ridge of the Brazil Basin in the South Atlantic (Polzin et al, 1997) In these regions, interactions between tidal flows and bottom topography are known to be important. We report near-inertial flows with a vertically coherent phase but varying amplitude with depth obtained in more extensive observations undertaken in the Yamato and Tsushima Basins in the southern Japan Sea and try to explain the observed deep flow characteristics by the superposition of vertically propagating NIWs. The reflection of internal waves off a sloping bottom and consequent flow intensification have been studied theoretically and observationally (e.g., Eriksen, 1982; Phillips, 1977; Sarkar & Scotti, 2017).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
