SPECIAL SECTION: ORIGINAL ARTICLE Regional Environmental Oceanography in the South China Sea and Its Adjacent Areas (REO-SCS): II Variability of sea surface temperature and warm pool area in the South China Sea and its relationship to the western Pacific warm pool Chun-Yi Lin • Chung-Ru Ho • Quanan Zheng • Shih-Jen Huang • Nan-Jung Kuo Received: 30 August 2010 / Revised: 25 May 2011 / Accepted: 9 August 2011 / Published online: 5 October 2011 Ó The Oceanographic Society of Japan and Springer 2011 Abstract Sea surface temperature (SST) data derived from satellite and in situ measurements are used to study the thermal variability in the South China Sea (SCS). Time–frequency–energy distributions, periods of variabil- ity, and trends are computed by the Hilbert–Huang trans- form method. The SST trend from 1982 to 2005 is 0.276°C per decade in the SCS which is higher than 0.144°C per decade in the western Pacific warm pool (WPWP). The warm pool (SST C 28°C) area in the SCS has increased by 0.20 9 10 6 km 2 per decade. The SST and area of the warm pool in the SCS are strongly correlated, respectively, with the SST and area of the WPWP with a time lag of 1 month, suggestive of a strong connection between these two warm pools. Once the annual cycle is eliminated, decadal oscil- lations dominate the variability of SST and warm pool area in the SCS. Keywords South China Sea Á Sea surface temperature Á Western Pacific warm pool Á Hilbert–Huang transform Á Trend 1 Introduction The global heat budget is strongly influenced by the trop- ical Pacific Ocean. The western Pacific warm pool (WPWP) in the tropical Pacific Ocean has the warmest sea surface temperature (SST) and the largest warm water mass of all the world’s oceans (Yan et al. 1992; Ho et al. 1995). The warm pool is conventionally defined as an area where SST is at least 28°C. Numerous studies have shown that the WPWP has a strong influence on the climate of sur- rounding areas such as the South China Sea (SCS) (Liu et al. 2004; Qu et al. 2004; Li et al. 2007; Zheng et al. 2007). The SCS is the world’s largest marginal sea with an area of approximately 3,500,000 km 2 . The bottom topography of the sea is characterized by two extended continental shelves on the northern and the southern sides and a deep basin with a maximum depth of more than 5000 m situated in the central-eastern portion. The deep basin occupies 44% of the total area of the SCS (Li et al. 2007; Lin et al. 2008). The SCS has warm water with an SST of at least 28°C during most of year as a part of the WPWP. Zheng et al. (2007) studied the interaction between the SCS eddy and the west Pacific water influx, which is affected by El Nin ˜o- Southern Oscillation (ENSO). Qu et al. (2004) also sug- gested that water exchange through the Luzon Strait may have an important role in conveying the impact of the Pacific ENSO to the SCS. Thermal variability in the SCS is strongly influenced by the WPWP because a large amount of western Pacific water flows into the SCS. It has also been suggested that the SCS affects the Southeast Asian monsoon system and the climate of China, and even the whole of East Asia (Lau 1997). Therefore variations of intensity and size of the SCS warm pool may strongly impact on hydrography and climatology of the surrounding areas. The estimated increase of observed global ocean heat content between the 1950s and 1990s was unprecedented (Levitus et al. 2001). The tropical Pacific plays a key role in the global oceanic heat budget and its variation is C.-Y. Lin Á C.-R. Ho (&) Á S.-J. Huang Á N.-J. Kuo Department of Marine Environmental Informatics, National Taiwan Ocean University, Keelung, Taiwan e-mail: b0211@mail.ntou.edu.tw Q. Zheng Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD, USA 123 J Oceanogr (2011) 67:719–724 DOI 10.1007/s10872-011-0072-x