For investigation of internal solitary waves (ISWs) in the South China Sea (SCS), most cruise observations are concentrated from Luzon Strait to Dongsha Atoll in the northeastern SCS, but few on the continental slope far away from the west of Dongsha Atoll. In this study, we use one‐year long mooring data to determine dynamic and statistical features of the ISWs on the shelf slope of the northwestern SCS. The analysis results of the mooring data reveal that the ocean internal waves (IWs) on the shelf slope of the northwestern SCS have physical properties of highly non‐linear waves, which are well described by the solutions of the KdV equation. The mean nonlinear phase speeds of mode‐1 and mode‐2 ISWs are 1.38 ± 0.14 m s⁻¹ and 0.66 ± 0.12 m s⁻¹, respectively. The major direction of mode‐1 ISWs is northwestward 305° ± 21°. Strong ISW currents force the major direction of total current velocities to turn 67.5° in the upper layer and 135° in the lower layer. The monthly occurrence frequency distribution of ISWs shows a peak in July with a maximum frequency of 16.2% and a trough in March with a minimum frequency of 3.3%. Mode‐2 ISWs appear most in December, accounting for 50% of total mode‐2 ISWs. The largest mode‐2 ISW on record up today with the depressed amplitude as large as 91 m and the elevated amplitude of 73 m was observed at mooring station. These new findings and new data are of significance to local IW prediction model development.

The generation of nonlinear internal waves (NLIWs) by stratified tidal flow over an isolated topography has been a subject of research for many years. However, the enhanced complexity of the dynamics as a consequence of flow over two topographical features has been less studied and understood. Here, we report results of the generation of type‐A and type‐B NLIWs in the South China Sea that originate from a double‐ridge system. Based on a realistic three‐dimensional nonhydrostatic simulation, it is found that type‐A NLIWs are generated at the western ridge through the mechanism of internal tide release, while the generation of type‐B NLIWs occurs at the eastern ridge as a consequence of internal wave interaction. Associated with the ridge height, separation distance, and modulated tidal forcing, the generation of type‐B NLIWs is strongly modified by the resonant process between the two ridges. As a result, type‐A and type‐B NLIWs appear in the observations with alternating large and small amplitudes. In addition, with a detailed knowledge of the generation, it is also found that the different arrival time of these waves could be due to their different generation times. Finally, the reflection/transmission of type‐B NLIWs at the subcritical western ridge is suggested as a key feature of resonance. However, it is governed by hydraulically controlled flow instead of the ratio of the local topographic slope to the internal wave beam angle.

The influences of grouped anticyclonic eddies (AEs) in the ocean on the intensity of tropical cyclone (TC) in the atmosphere are investigated in the present study. The research was carried out using numerical methods taking the development of TC Hato (2017) in the northern South China Sea (SCS) as an example. Three AEs were observed, one at the TC track (defined as the inner area) and the other two in the south of the TC center (defined as the outer area), at about three times the radius of maximum wind speed. The results show that the outer AEs suppress TC development, but the inner AEs greatly favor TC development. This opposite influence primarily results from the different responses of TC secondary circulation to the AE‐induced local sea surface warm anomaly in the inner and outer areas. The outer AE triggers a low sea level pressure anomaly and convergent wind toward the AE, which weakens TC inflow at the lower layers and further weakens TC secondary circulation. Consequently, the energy conversion from ocean heat energy to TC kinetic energy is decreased by the weakened TC secondary circulation. The AE in the outer area also extends the TC eyewall, weakens the TC warm core, and increases the outer precipitation. As a result, the TC intensity is weakened. The inner AE causes opposite changes in TC secondary circulation, eyewall, warm core, and outer precipitation, so that favors TC development. These results provide evidence for the suppression effect of the outer AEs on TC development, providing a new perspective toward improving TC intensity forecasts.

Based on the temperature data recorded by a mooring system deployed in the northern South China Sea (SCS), this study compares the traditional methods of identifying and extracting internal solitary waves (ISWs): the whole water column isotherm (WCI) method and the single isotherm (SI) method, and proposes a novel method: the temperature superposition (TS) method. Results indicate that the TS method identifies the most ISWs, followed by the WCI method, and the SI method identifies the fewest. When the ISW amplitudes are smaller than 60 m, the TS method can identify the most ISWs. When the ISW amplitudes are greater than 60 m, the number of ISWs identified by the three methods is the same. The TS method removes the internal tides, takes into account the temperature of all depth layers, and amplifies the signal of ISWs to a certain extent, so as to effectively identify ISWs.