Interannual variability in the South China Sea from expendable bathythermograph data (original) (raw)

1999, Journal of Geophysical Research

Using 29 years of expendable bathythermograph data, we studied the interannual temperature variability in the upper 300 m of the South China Sea (SCS). It is found that the temperature field has significant quasi-penta-annual variability throughout the 29 years. The interannual variability has a large decadal modulation. Although outside the SCS, in the Kuroshio, significant interannual variability extends to a much deeper layer beyond the 300 m depth, inside the SCS, especially in the central SCS, strong interannual variability is located near the 100 m depth and is capped by a surface layer of much weaker interannual variability. Similarities and differences in the temporal characteristics between the interannual variability inside and outside the SCS suggest that the interannual variability inside the SCS is primarily generated locally inside the SCS. In addition to the strong interannual variability, there exist strong decadal variability and a linear trend, which are also stronger in the subsurface than near the surface. It is found that below 100 m, the SCS has been cooling (linear trend) at a rate of-•0.4øC per decade, decreasing from the eastern to the western basin. 1. Introduction The tropical western Pacific region has increasingly become the focus of both theoretical and observational studies, given its pivotal role in the E1 Nino, Indonesian throughflow, and low latitude and midlatitude exchange. Lukas et al. [1996] gave a comprehensive review of studies related to the three-dimensional circulation and its temporal variability in the tropical western Pacific region. Most studies on interannual to decadal variability have focused on variabilities outside the South China Sea (SCS) in the open ocean [e.g., Rasmusson et al., 1990; Miller et al., 1997; Zhang and Levitus, 1997a, b; Miller et al., 1998], even though the SCS is one of the largest marginal seas in the world (the rim of the SCS is the most heavily populated region in the world) and is connected to the western North Pacific through the Luzon Strait between Taiwan and the Philippines, as shown in Figure 1. The SCS is under the Southeast Asian Monsoon [Lau and Yang, 1997], which reverses its direction between summer and winter.