5:15 PM - 6:30 PM
[ACG38-P03] Statistical analysis of ocean waves in the sea of Japan
Keywords:wave height, Sea of Japan
Wave climate is important for marine disaster prevention. The Sea of Japan is a semi-enclosed sea that connects the Tsushima Strait and the Mamiya Strait to other sea areas. Therefore, waves in the Japan Sea are more influenced by local winds than by distant swells. In this study, we investigated the interannual variability of the wave height distribution using the ERA5 reanalysis data. First, we compared the wave heights by ERA5 with those by GPS buoys around Japan. The agreement between them is good. Next, the difference in the accuracy of the ERA5 wave height was compared between the short and long fetch cases. In the short fetch case, the accuracy of the ERA5 wave heights is significantly lower than that of the long fetch case.
Wave heights by ERA5 and those by JMA (Japan Meteorological Agency) moored buoys (1990 to 2000) were compared. The agreement between them was good. In addition, the accuracy of ERA5 wave height after incorporating altimeter data into ERA5 wave data from 1992 was compared with those of wave height before that. The difference in the accuracy between them was small.
Next, the spatial distribution of ERA5 monthly mean wave height anomalies from climatological values from 1979 to 2019 was examined by empirical orthogonal function (EOF) analysis. The first mode is a pattern of variability in the central region of the sea of Japan (around 40N, 135E). The second mode is a pattern that fluctuates alternately in the north and south of the Sea of Japan (around 35N, 131E and 45N, 140E). The correlation between the EOF time series of monthly mean wind anomalies and the EOF time series of wave height anomalies was investigated. The first mode of wave height anomalies is correlated with the second mode of EOF wind anomalies over almost the entire Japan Sea area. The second EOF mode of wave height anomaly is correlated with the first EOF mode of wind anomaly in the northern part of the sea of Japan.
The monthly wave height anomaly maps were classified by self-organizing map analysis. Some frequent wave height anomaly maps corresponded to the distributions of EOF first and second modes of wave height anomaly. The frequency of the distribution patterns with high wave height anomaly in the central area of the sea of Japan has been increasing in recent years. This is consistent with the trend of the EOF first mode time series of wave height anomalies. In addition, wave height anomalies in the northern and southern areas of the sea of Japan corresponded most closely to the distribution patterns of wind anomalies in the northern area of the sea of Japan. This is consistent with the result that the second EOF mode of wave height anomalies is correlated with the first EOF mode of wind anomalies in the northern part of the sea of Japan.
Wave heights by ERA5 and those by JMA (Japan Meteorological Agency) moored buoys (1990 to 2000) were compared. The agreement between them was good. In addition, the accuracy of ERA5 wave height after incorporating altimeter data into ERA5 wave data from 1992 was compared with those of wave height before that. The difference in the accuracy between them was small.
Next, the spatial distribution of ERA5 monthly mean wave height anomalies from climatological values from 1979 to 2019 was examined by empirical orthogonal function (EOF) analysis. The first mode is a pattern of variability in the central region of the sea of Japan (around 40N, 135E). The second mode is a pattern that fluctuates alternately in the north and south of the Sea of Japan (around 35N, 131E and 45N, 140E). The correlation between the EOF time series of monthly mean wind anomalies and the EOF time series of wave height anomalies was investigated. The first mode of wave height anomalies is correlated with the second mode of EOF wind anomalies over almost the entire Japan Sea area. The second EOF mode of wave height anomaly is correlated with the first EOF mode of wind anomaly in the northern part of the sea of Japan.
The monthly wave height anomaly maps were classified by self-organizing map analysis. Some frequent wave height anomaly maps corresponded to the distributions of EOF first and second modes of wave height anomaly. The frequency of the distribution patterns with high wave height anomaly in the central area of the sea of Japan has been increasing in recent years. This is consistent with the trend of the EOF first mode time series of wave height anomalies. In addition, wave height anomalies in the northern and southern areas of the sea of Japan corresponded most closely to the distribution patterns of wind anomalies in the northern area of the sea of Japan. This is consistent with the result that the second EOF mode of wave height anomalies is correlated with the first EOF mode of wind anomalies in the northern part of the sea of Japan.