**1. Introduction**

Internal solitary waves (ISWs) are ubiquitous in some marginal seas, especially in the South China Sea (SCS) [1]. They are supposedly generated near the Batan Islands of Luzon Strait and propagate northwestward in the deep basin with long crest lengths ranging from about 100 to 250 km [2,3], then shoal onto the continental shelf and finally dissipate on the plateau [4].

ISWs have rapid spatial evolution in shallow water [5], and they have been extensively studied near Dong-Sha Atoll by in situ measurements, remote sensing, and numerical simulations. Strong ISWs have been observed near Dong-Sha Atoll by moorings and shipboard surveys with amplitudes ranging from 70 to 173 m and peak westward velocities from 0.73 to 2.4 m/s [4–12].

However, one ISW with a peak westward current velocity of 2.94 m/s northeast of Dong-Sha Atoll is presented in this paper, with the largest ISW velocity ever observed in the global ocean.

This paper is organized as follows. Section 2 gives a general representation of the data. The description of measurements and the phase speed analysis are provided in Section 3. The discussion follows in Section 4, which includes the impact of the barotropic tide, the trapped core, and the breaking stage. Finally, a conclusion is given in Section 5.

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**Citation:** Xu, A.; Chen, X. A Strong Internal Solitary Wave with Extreme Velocity Captured Northeast of Dong-Sha Atoll in the Northern South China Sea. *J. Mar. Sci. Eng.* **2021**, *9*, 1277. https://doi.org/10.3390/ jmse9111277

Academic Editor: Lev Shemer

Received: 7 October 2021 Accepted: 10 November 2021 Published: 17 November 2021

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