Causes of seasonal sea level anomalies in the coastal region of the East China Sea

Based on the analysis of sea level, air temperature, sea surface temperature (SST), air pressure and wind data during 1980-2013, the causes of seasonal sea level anomalies in the coastal region of the East China Sea (ECS) are investigated. The research results show: (1) sea level along the coastal region of the ECS takes on strong seasonal variation. The annual range is 30-45 cm, larger in the north than in the south. From north to south, the phase of sea level changes from 140 degrees to 231 degrees, with a difference of nearly 3 months. (2) Monthly mean sea level (MSL) anomalies often occur from August to next February along the coast region of the ECS. The number of sea level anomalies is at most from January to February and from August to October, showing a growing trend in recent years. (3) Anomalous wind field is an important factor to affect the sea level variation in the coastal region of the ECS. Monthly MSL anomaly is closely related to wind field anomaly and air pressure field anomaly. Wind-driven current is essentially consistent with sea surface height. In August 2012, the sea surface heights at the coastal stations driven by wind field have contributed 50%-80% of MSL anomalies. (4) The annual variations for sea level, SST and air temperature along the coastal region of the ECS are mainly caused by solar radiation with a period of 12 months. But the correlation coefficients of sea level anomalies with SST anomalies and air temperature anomalies are all less than 0.1. (5) Seasonal sea level variations contain the long-term trends and all kinds of periodic changes. Sea level oscillations vary in different seasons in the coastal region of the ECS. In winter and spring, the oscillation of 4-7 a related to El Nino is stronger and its amplitude exceeds 2 cm. In summer and autumn, the oscillations of 2-3 a and quasi 9 a are most significant, and their amplitudes also exceed 2 cm. The height of sea level is lifted up when the different oscillations superposed. On the other hand, the height of sea level is fallen down.