Analysis of monthly variability of thermocline in the South China Sea

This study analyzes monthly variability of thermocline and its mechanism in the South China Sea （SCS）. The study is based on 51-year （1960-2010） monthly seawater temperature and surface wind stress data from Simple Ocean Data Assimilation （SODA）, together with heat flux, precipitation and evaporation data from the National Centers for Environmental Prediction （NCEP）, the National Oceanic and Atmospheric Administration （NOAA） and the Woods Hole Oceanographic Institution, respectively. The results reveal that the upper boundary depth （Zup）, lower boundary depth （Zlow）, thickness （AZ） and intensity （Tz） of thermocline in the SCS show remarkable monthly variability. Being averaged for the deep basin of SCS, Zup deepens gradually from May to the following January and then shoals from February to May, while Zow varies little throughout the whole year. Further diagnostics indicates that the monthly variability of Zup is mainly caused by the buoyancy flux and wind stress curl. Using a linear method, the impacts of the buoyancy flux and wind stress curl on Zup can be quantitatively distinguished. The results suggest that Zup tends to deepen about 4.6 m when the buoyancy flux increases by 1 × 10.5 kg/（m·s3）, while it shoals about 2.5 m when the wind stress curl strengthens by 1 × 10-7 N/m3.

A study of response of thermocline in the South China Sea to ENSO events

This paper investigates the response of the thermocline depth(TD) in the South China Sea(SCS) to the El Ni?o-Southern Oscillation(ENSO) events using 51-year(from 1960 to 2010) monthly seawater temperature and surface wind stress data acquired from the Simple Ocean Data Assimilation(SODA), together with heat flux data from the National Centers for Environmental Prediction(NCEP), precipitation data from the National Oceanic and Atmospheric Administration(NOAA) and evaporation data from the Woods Hole Oceanographic Institution(WHOI). It is indicated that the response of the SCS TD to the El Ni?o or La Ni?a events is in opposite phase. On one hand, the spatial-averaged TDs in the SCS(deeper than 200 m) appear as negative and positive anomalies during the mature phase of the El Ni?o and La Ni?a events, respectively. On the other hand, from June of the El Ni?o year to the subsequent April, the spatial patterns of TD in the north and south of 12°N appear as negative and positive anomalies, respectively, but present positive and negative anomalies for the La Ni?a case. However, positive and negative TD anomalies occur almost in the entire SCS in May of the subsequent year of the El Ni?o and La Ni?a events, respectively. It is suggested that the response of the TD in the SCS to the ENSO events is mainly caused by the sea surface buoyancy flux and the wind stress curl.