Characteristics and possible causes of the seasonal sea level anomaly along the South China Sea coast

Based on sea level, air temperature, sea surface temperature (SST), air pressure and wind data during 1980-2014, this paper uses Morlet wavelet transform, Estuarine Coastal Ocean Model (ECOM) and so on to investigate the characteristics and possible causes of seasonal sea level anomalies along the South China Sea (SCS) coast. The research results show that:(1) Seasonal sea level anomalies often occur from January to February and from June to October. The frequency of sea level anomalies is the most in August, showing a growing trend in recent years. In addition, the occurring frequency of negative sea level anomaly accounts for 50% of the total abnormal number. (2) The seasonal sea level anomalies are closely related to ENSO events. The negative anomalies always occurred during the El Niño events, while the positive anomalies occurred during the La Ni.a (late El Niño) events. In addition, the seasonal sea level oscillation periods of 4-7 a associated with ENSO are the strongest in winter, with the amplitude over 2 cm. (3) Abnormal wind is an important factor to affect the seasonal sea level anomalies in the coastal region of the SCS. Wind-driven sea level height (SSH) is basically consistent with the seasonal sea level anomalies. Moreover, the influence of the tropical cyclone in the coastal region of the SCS is concentrated in summer and autumn, contributing to the seasonal sea level anomalies. (4) Seasonal variations of sea level, SST and air temperature are basically consistent along the coast of the SCS, but the seasonal sea level anomalies have no much correlation with the SST and air temperature.