ADVANCES IN ATMOSPHERIC SCIENCES, VOL. 27, NO. 2, 2010, 265–273 The Cold Tongue in the South China Sea during Boreal Winter and Its Interaction with the Atmosphere Hamza VARIKODEN ∗ , A. A. SAMAH, and C. A. BABU National Antarctic Research Centre, University of Malaya, IPS Building, Kuala Lumpur-50603, Malaysia (Received 9 September 2008; revised 14 May 2009) ABSTRACT A distinct cold tongue has recently been noticed in the South China Sea during the winter monsoon, with the cold tongue temperature minimum occurring in the January or February. This cold tongue shows significant links with the Maritime Continent’s rainfall during the winter period. The cold tongue and its interaction with the Maritime Continent’s weather were studied using Reynolds SST data, wind fields from the NCEP–NCAR reanalysis dataset and the quikSCAT dataset. In addition, rainfall from the GOES Precipitation Index (GPI) for the periods 2000 to 2008 was also used. The propagation of the cold tongue towards the south is explained using wind dynamics and the western boundary current. During the period of strong cold tongue, the surface wind is strong and the western boundary current advects the cold tongue to the south. During the period of strong winds the zonal gradient of SST is high [0.5 ◦ C (25 km) -1 ]. The cold tongue plays an important role in regulating the climate over the Maritime Continent. It creates a zonal/meridional SST gradient and this gradient ultimately leads in the formation of convection. Hence, two maximum precipitation zones are found in the Maritime Continent, with a zone of relatively lower precipitation between, which coincides with the cold tongue’s regions. It was found that the precipitation zones have strong links with the intensity of the cold tongue. During stronger cold tongue periods the precipitation on either side of the cold tongue is considerably greater than during weaker cold tongue periods. The features of convection on the eastern and western sides of the cold tongue behave differently. On the eastern side convection is preceded by one day with SST gradient, while on the western side it is four days. Key words: cold tongue, SST gradient, wind, precipitation Citation: Varikoden, H., A. A. Samah, and C. A. Babu, 2010: The cold tongue in the South China Sea during boreal winter and its interaction with the atmosphere. Adv. Atmos. Sci., 27(2), 265–273, doi: 10.1007/s00376-009-8141-4. 1. Introduction The South China Sea (SCS) is the largest marginal sea in Southeast Asia, with a basin deeper than 4000 m in the central region and surrounded by a large con- tinental shelf of less than 200 m in depth (Shaw and Chao, 1994). It is connected with the East China Sea to the northeast, the Pacific and the Sulu Sea to the east, and the Java Sea and Indian Ocean to the south- west. The SCS is an integral part of the East Asian monsoon system (Wyrtki, 1961; Lau et al., 1998). The SST of the SCS is an important factor in the develop- ment and evolution of the East Asian monsoon. Many studies have revealed that the SCS SST shows an in- terannual variation that is closely associated with the interannual variation of the East Asian monsoon (Shen and Lau, 1995; Tomitha and Yasunari, 1996; Chu and Chang, 1997; Wen et al., 2000) and also with ENSO episodes (Lim and Tuen, 1991; Liu et al., 2004). Lim and Tuen (1991) reported that the SCS SST shows marked intraseasonal and interannual variabilities and suggested more detailed studies for linking these vari- abilities with weather events in the SCS and neighbor- ing continents. In the SCS the seasons play a vital role for regulating SST. In winter the SCS is dominated by strong northeasterly winds, whereas in summer the di- ∗ Corresponding author: Hamza VARIKODEN, hamzavarikoden@gmail.com Current affiliation: Climatology and Hydrometeorology Division, Indian Institute of Tropical Meteorology, Pashan, Pune 411 008, India