Fig. 1

(a) MODIS/Terra RGB image acquired on 22 August 2020 at 12:10 UTC+8. The yellow arrows mark the crest lines of ISWs. The red dashed lines highlight the area around the Dongsha Island. The red star marks Station IW1, which water depth is 3000 m. The green star marks mooring Station IW6, which water depth is 323 m. The yellow arrow marks the crest lines of ISWs. Satellite imagery courtesy of the NASA Worldview application (https://worldview.earthdata.nasa.gov), part of the NASA Earth Observing System Data and Information System (EOSDIS). Geospatial axes and all scientific annotations were subsequently added using MATLAB R2024b (http://www.mathworks.com/). (b) Background water temperature profile measured by CTD. The red triangle marked the background SST. (c) Velocity components profiles of the background velocity \({\mathbf{u}}_{{\mathbf{b}}}\). The current velocity from −20 m to 0 m is supplemented by nearest interpolation. (d) Schematic diagram of the relative position of the data analysis area of WaMoS II system (three red rectangles) to the ISW front (blue shadow). \(\theta\) is the propagation direction of the ISW. \(\varphi\) is the angle between \(\theta\) and the ship heading. The orange arrows denote the directions along and across the propagation direction of the ISW. At 12:10 a.m., the wind speed (\(\left| {{\mathbf{U}}_{{\mathbf{a}}} } \right|\)), ship heading, and wind direction (\(Dir_{a}\)) are 8.95 m·s⁻¹, 305°, and 215° (0° pointing east), respectively. (e) Drift trajectory and drift speed of R/V DFH3 during the experiment