Deep circulation in the South China Sea simulated in a regional model
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Deep circulation in the South China Sea simulated in a regional model Xiaolong Zhao 1,2 & Chun Zhou 2 & Xiaobiao Xu 3 & Ruijie Ye 2,4 & Wei Zhao 2 Received: 8 March 2020 / Accepted: 15 September 2020 / Published online: 29 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this study, deep circulation in the South China Sea (SCS) is investigated using results from mesoscale-eddy-resolving, regional simulations using the Hybrid Coordinate Ocean Model (HYCOM) verified by continuous current-meter observations. Analysis of these results provides a detailed spatial structure and temporal variability of the deep circulation in the SCS. The major features of the SCS deep circulation are a basin-scale cyclonic gyre and a concentrated deep western boundary current (DWBC). Transport of the DWBC is ~ 2 Sv at 16.5°N with a width of ~ 53 km. Flowing southwestward, the narrow DWBC becomes weaker and wider. The model results reveal the existence of 80- to 120-day oscillation in the deep northeastern circulation and the DWBC, which are also the areas with elevated eddy kinetic energy. This intraseasonal oscillation propagates northwestward with a velocity amplitude of ~ 1.0 to 1.5 cm s−1. The distribution of mixing parameters in the deep SCS plays a role in both spatial structure and volume transport of the deep circulation. Compared with the northern shelf of the SCS and the Luzon Strait, deep circulation in the SCS is more sensitive to the large vertical mixing parameters of the Zhongsha Island Chain area. Keywords Deep circulation . South China Sea . Spatial structure . Temporal variability . Mixing
1 Introduction The South China Sea (SCS, Fig. 1) is the largest marginal sea in the Southeast Asian Waters, with an area of approximately 3.5 × 106 km2 and a depth exceeding 4000 m in the central basin (Wyrtki 1961). It is connected to the surrounding waters Responsible Editor: Fanghua Xu Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10236-020-01411-2) contains supplementary material, which is available to authorized users. * Chun Zhou [email protected] 1
North China Sea Marine Forecasting Center, State Oceanic Administration, Qingdao 266061, People’s Republic of China
2
Key Laboratory of Physical Oceanography/CIMST, Ocean University of China and Qingdao National Laboratory for Marine Science and Technology, Qingdao 266100, People’s Republic of China
3
Center for Ocean-Atmospheric Prediction Studies (COAPS), Florida State University, Tallahassee, FL, USA
4
State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, People’s Republic of China
mostly by shallow straits: Taiwan Strait to the East China Sea in the north, the Karimata Strait to the Java Sea in the south, and the Mindoro Strait to the Sulu Sea in the southeast. The 355-km-wide Luzon Strait, with a sill depth of ~ 2400 m, is the only deep connection between the SCS and its ambient oceans. There,
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