Abstract
Satellite altimeter data from 1993 to 2005 has been used to analyze the seasonal variation and the interannual variability of upper layer thickness (ULT) in the South China Sea (SCS). Base on in-situ measurements, the ULT is defined as the thickness from the sea surface to the depth of 16°C isotherm which is used to validate the result derived from satellite altimeter data. In comparison with altimeter and in-situ derived ULTs yields a correlation coefficient of 0.92 with a slope of 0.95 and an intercept of 6 m. The basin averaged ULT derived from altimeter is 160 m in winter and 171 m in summer which is similar to the in-situ measurements of 159 m in winter and 175 m in summer. Both results also show similar spatial patterns. It suggests that the sea surface height data derived from satellite sensors are usable for study the variation of ULT in the semi-closed SCS. Furthermore, we also use satellite derived ULT to detect the development of eddy. Interannual variability of two meso-scale cyclonic eddies and one anticyclonic eddy are strongly influenced by El Niño events. In most cases, there are highly positive correlations between ULT and sea surface temperature except the periods of El Niño. During the onset of El Niño event, ULT is deeper when sea surface temperature is lower.
Highlights
The South China Sea (SCS) is the largest marginal sea at the westernmost side of the tropicalPacific Ocean
Variations of monthly mean upper layer thickness (ULT) in the SCS are derived from in-situ measurements from 1980 to 2005 and satellite altimeter data from 1993 to 2005
The depth of the 16°C isotherm is chosen as definition of the thickness of upper layer
Summary
The South China Sea (SCS) is the largest marginal sea at the westernmost side of the tropical. The sea surface temperature (SST) is a major signature of upper ocean thermal processes. It is affected by upper layer variability to a large extent. The estimates of upper layer thickness (ULT) from satellite altimeter data have been studied since. Garzoli et al [10] used the altimeter data derived ULT to monitor the upper layer transport in the southeastern Atlantic Ocean. A further application of altimeter data derived ULT is to study the heat storage in the upper layer combined with sea surface temperature [13,14,15,16]. The applications of satellite derived ULT are most in the open oceans; in this study we validate the usability of this estimation in a semi-closed sea.
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