INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 34: 2651–2660 (2014) Published online 21 November 2013 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/joc.3865 Comparison of the impact of two types of El Ni ˜ no on tropical cyclone genesis over the South China Sea Xin Wang, a Wen Zhou, b * Chongyin Li c and Dongxiao Wang a a State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China b Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong, Hong Kong, China c State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China ABSTRACT: This study examines the impact of the cold tongue (CT) El Ni˜ no and the warm pool (WP) El Ni˜ no on tropical cyclone (TC) genesis over the South China Sea (SCS) from 1965 to 2010. During Sept–Oct–Nov (SON), the TC genesis exhibits clear interannual variability. SON TC genesis is significantly related with the WP Ni˜ no index, but not with the CT Ni˜ no index. It is found that in the past two decades the SCS TC genesis varies coherently with the WP Ni˜ no index on a timescale of approximately 4 years, which is in accordance with the recent increase in WP El Ni˜ no events. The distinctly different atmospheric teleconnection patterns related to the CT and WP El Ni˜ no over the SCS are responsible for these relationships. CT El Ni˜ no can induce anticyclone anomalies over the SCS and the western tropical Pacific WP. However, WP El Ni˜ no can result in dipolar patterns with anticyclone anomalies over the SCS and cyclone anomalies over the western tropical Pacific WP at low- and mid-level. These WP El Ni˜ no-related large-scale circulation anomalies enlarge the low-level northerlies over the SCS. This in turn enhances the vertical wind shear and thus suppresses TC genesis over the SCS. KEY WORDS warm pool and cold tongue El Ni˜ no; tropical cyclone; South China Sea Received 11 July 2012; Revised 4 September 2013; Accepted 9 October 2013 1. Introduction The South China Sea (SCS), located in Southeast Asia roughly between the equator and 22 ◦ N and from 105–120 ◦ E, is a region with a high frequency of tropi- cal cyclone (TC) genesis (Camargo et al., 2007; Wang et al., 2007; Yan et al., 2012). Many previous studies have demonstrated that the El Ni˜ no-Southern Oscillation (ENSO) can influence the interannual variability of TC genesis over the SCS and western North Pacific to some extent (Li, 1988; Lee et al., 2006; Wang et al., 2007; Li and Zhou, 2012; Li et al., 2012; Wang and Wang, 2013a). Wang and Chan (2002) suggested that during summer and fall between strong El Ni ˜ no and La Ni ˜ na, the frequency of TC formation is remarkable changed in the southeast and northwest quadrants of the western North Pacific. Zuki and Lupo (2008) further elucidated that more (less) TC activity over Malaysia and regions around (in the south- ern SCS) during November and December is observed in La Ni˜ na (El Ni˜ no) years during 1960–2006. Besides ENSO, the TC geneses over the SCS are suggested to closely connect with the East Asian monsoon on differ- ent time scales (Wang et al., 2007; Zhou and Chan, 2007; * Correspondence to: Dr. W. Zhou, Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong, Kowloon, Hong Kong, China. E-mail: wenzhou@cityu.edu.hk Yuan et al., 2008; Feng et al., 2011; Wang et al., 2012; Li et al., 2013). In recent years, a number of studies have revealed a new type of El Ni˜ no, which is different from the canonical El Ni˜ no in terms of the location of the maximum sea surface temperature (SST) anomalies. Usually referred to as ‘Dateline El Ni˜ no’ (Larkin and Harrison, 2005), ‘El Ni˜ no Modoki’ (Ashok et al., 2007), ‘Central Pacific El Ni˜ no’ (Yu and Kao, 2007) or ‘warm pool El Ni˜ no’ (Kug et al., 2009), this new type of El Ni˜ no has significantly different El Ni˜ no-induced tropical- midlatitude teleconnections (Larkin and Harrison, 2005; Ashok et al., 2007; Kao and Yu, 2009; Weng et al., 2009; Yu and Kim, 2010; Wang and Wang, 2013b). In this study, the name of warm pool (WP) El Ni˜ no is used. Interest in the impact of the new type of El Ni˜ no on TC activity has been rapidly increasing (Kim et al., 2009; Lee et al., 2010; Chen and Tam, 2010; Kim et al., 2012a; Wang et al., 2013; Wang and Wang, 2013a). For example, Kim et al. (2009) suggested that compared to eastern Pacific warming events, central Pacific warming events are associated with an above-normal-level TC frequency and increasing landfall potential along the gulf of Mexico coast and Central America. Lee et al. (2010) further suggested that the Atlantic WP could readily explain the increased tropical storm frequency even in central Pacific warming years, such as 1969 and 2004. The changes in TC frequency are associated with the modulation of  2013 Royal Meteorological Society