The long-term trends of sea surface wind are of great importance to our understanding of the effects of climate change on the marine environment. In the northern South China Sea (SCS), the long-term changes in coastal sea surface wind are not well-understood. Based on the latest reanalysis (ERA5) data from 1979 to 2019, our analysis showed a decreasing trend in the annual mean wind speed in the coastal area and an increasing trend in the open sea. There was a significant weakening trend in the easterly wind component in the coastal and continental shelf areas, whereas there was an increasing trend in the northerly wind component in the open sea. The Mann–Kendall mutation analysis suggested that there were significant changes in the wind speed and frequency of strong wind. Significant correlations were found between the variation of the wind field and El Nino–Southern Oscillation by wave coherence analysis. The strengthening of the wind stress curl was an important factor for the enhancement of coastal upwelling along the coast of the northern SCS. The wind field plays an important role in modulating the climatic change of significant wave height.

Long-Term Trends of Sea Surface Wind in the Northern South China Sea under the Background of Climate Change

The seasonal variability of the significant wave height (SWH) in the South China Sea (SCS) is investigated using the most up-to-date gridded daily altimeter data for the period of September 2009 to August 2015. The results indicate that the SWH shows a uniform seasonal variation in the whole SCS, with its maxima occurring in December/January and minima in May. Throughout the year, the SWH in the SCS is the largest around Luzon Strait (LS) and then gradually decreases southward across the basin. The surface wind speed has a similar seasonal variation, but with different spatial distributions in most months of the year. Further analysis indicates that the observed SWH variations are dominated by swell. The wind sea height, however, is much smaller. It is the the largest in two regions southwest of Taiwan Island and southeast of Vietnam Coast during the northeasterly monsoon, while the largest in the central/southern SCS during the southwesterly monsoon. The extreme wave condition also experiences a significant seasonal variation. In most regions of the northern and central SCS, the maxima of the 99th percentile SWH that are larger than the SWH theoretically calculated with the wind speed for the fully developed seas mainly appear in August–November, closely related to strong tropical cyclone activities. Compared with previous studies, it is also implied that the wave climate in the Pacific Ocean plays an important role in the wave climate variations in the SCS.

Revisiting the seasonal wave height variability in the South China Sea with merged satellite altimetry observations

Dynamics of the seasonal wave height variability in the South China Sea

Based upon the one-year wind wave measurement data, collected from the South China Sea (SCS) at coordinates 20° 36.298′N, 110°45.433′E. by Acoustic Wave And Current (AWAC), we analyzed the wave characteristics and concluded that the most common wave direction was E and the second most common direction was ENE, the mean and the maximum values of significant height was 1.2 m and 4.36 m, respectively. The mean period was 4.0 s. We also evaluated the wave spectrums under conditions existing in three typhoons: Rumbi, Jeti and Utor. We found that unimodal spectrums occurred more often than others, and the maximum spectrum peak was 30.7911 m2 s. The minimum peak frequency was 0.0625 Hz, and the mean peak frequency was 0.126 Hz. The wave period is important for the design of marine structures, especially the position of peak frequency had a great influence on the stress calculation. Spectral analysis showed that the values of peak frequency distributed between 0.063 Hz and 0.217 Hz, with the mean value 0.114 Hz. We fit the normalized spectrum with 6 theoretical spectral models, out of which, the Wen spectrum, JONSWAP spectrum and Wallops spectrum were proved to give the best fit. What distinguished the Wen Spectrum from the rest was that it does not rely on the measured spectrum for parameter estimation. Hence, we recommend that the Wen spectrum should be widely used in marine construction.

The research on typhoon wave spectrum in northwestern South China Sea

Effects of currents on winter wind waves in the tide-dominated Qiongzhou Strait (QS) were numerically evaluated via employing the coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system. Validations showed satisfactory model performance in simulating the intense tidal currents in the QS. Different effects of sea level variations and tidal currents on waves were examined under the maximum eastward (METC) and westward (MWTC) tidal currents. In the east entrance area of the QS, the positive sea levels under the MWTC deepened the water depth felt by waves, benefiting the further propagation of wave energy into the inner strait and causing increased wave height. The METC and the MWTC could both enhance the wave height in the east entrance area of the QS, mainly through current-induced convergence and wavenumber shift, respectively. By current-induced refraction, the METC (MWTC) triggered counterclockwise (clockwise) rotation in peak wave directions in the northern part of the QS while clockwise (counterclockwise) rotation in the southern part.

Effects of tidal currents on winter wind waves in the Qiongzhou Strait: a numerical study

Due to the complex terrain and the many islands of the South China Sea,it will inevitably produce some nearshore processes,such as refraction,shallowing,diffraction,wave breaking,nonlinear wave interactions,etcSo,the third-generation wave model SWAN was used to simulate the wave fields of the South China Sea from January 1986 to December 2005In order to evaluate the wave energy resources reasonably and establish wave power stations on the sea,the seasonal characteristics,frequency of wave energy scale,the stability of the wave energy and wave energy statistics at different stances were analyzed

Zong Fangy

Papers

Research on Distributions and Variations of Wave Energy in South China Sea Based on Recent 20 Years' Wave Simulation Results Using Swan Wave Model