Swell and wind-wave height variability in the East China Sea

Wave climate is important for marine disaster prevention and marine development. The East China Sea is open to the Pacific Ocean and is considered to be greatly affected by swells. In this study, the variation of swell height and wind-wave height distribution was examined using ERA5 reanalysis data. In addition to the EOF (Empirical Orthogonal Function) analysis, the variability of wave height anomaly was examined by SOM (Self-Organizing Map). In this study, we clarify what phenomena can be detected by both SOM and EOF or only by either of them, in the area such as the East China Sea where the influence of swells is large. Patterns of SOM arrays corresponding to the eigenvector distribution maps of the first and second modes of the EOF of wave height anomaly were identified. However, there were some patterns in the major SOM array patterns of swell height anomaly that were not found in the EOF analysis. The most major wave height anomaly distributions are particularly frequent during the summer. Both the frequency of the most frequent SOM pattern of swell height anomaly and the first mode of EOF shows an increasing trend in swell height. In the East China Sea, the increasing trend of swell heights is more prominent during certain periods. The optimal region of the wind speed anomaly pattern was determined to best link with the swell height anomaly pattern in the East China Sea. The relationship between swell height anomaly patterns and wind speed anomaly patterns in the East China Sea varies with the seasons. Some climatic indices and wave height anomaly EOF time coefficients are correlated. The correlation is particularly high between the summer ENSO index and the swell height anomaly EOF first mode. This indicates that swell heights are higher during the ENSO period.