P 2 A . 10 THE INTERANNUAL VARIABILITY OF TROPICAL CYCLONE ACTIVITY IN THE SOUTHERN SOUTH CHINA SEA .

In recent years, there have been deadly tropical cyclones that have impacted the Southern South China Sea (SSCS) region, including Malaysia. Malaysia suffered direct strikes from tropical storm Greg on 25 December 1996 and tropical storm Vamei on 27 December 2001 (Chang et al. 2003). Also, the previously recorded lowest latitude for a typhoon was Sarah (3.3 N) in 1956 (Fortner, 1958). Additionally, Greg caused 238 deaths and economic losses of $52 M in US dollars (Ooi and Ling, 1996). These storms have caused concern in Malaysia as to whether or not this was part of a long-term trend toward more frequent tropical cyclone strikes. Tropical cyclones are among the most deadly and destructive of natural disasters in terms of loss of human life and economic destruction (Bengtsson et al., 1996). Thus, interest in research on tropical cyclones has increased substantially in recent years (e.g., Emanuel, 2005). This has been especially true regarding the study of intraseasonal and interannual variations in the intensity and occurrence of tropical cyclones, as associated with such phenomena as the Madden Julian Oscillation (MJO – e.g., Maloney and Hartmann, 2001), the Quasi-biennial Oscillation (QBO – e.g., Gray et al., 1984a,b; Chan, 1995), the El Niño and Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO) / North Atlantic Oscillation (NAO) (e.g., Gray et al., 1984a,b; Chan, 1985; Wu and Lau, 1992; Lander, 1994; O‘Brien et al., 1996; Bove et al., 1998; Landsea et al., 1999; Pielke and Landsea, 1999; Lupo and Johnston, 2000 hereafter LJ00; Houghton et al., 2001). LJ00 in their study of hurricane activity in the Atlantic region from 1944-1999 demonstrated that there was an interdecadal signal in the behavior of the ENSO response. This PDO variability could be described as there were more hurricane events per year during one phase of the PDO (e.g., 1947-1976), but little or no statistically significant ENSO variability. During the opposite phase of the PDO (1977 – 1998), there was strong ENSO-related variability in the __________________________________________________ *Corresponding author address: Anthony R. Lupo, Department of Soil, Environmental, and Atmospheric Science, 302 E ABNR Building, University of MissouriColumbia, Columbia, MO 65211. E-mail: LupoA@missouri.edu. intensity and number of Atlantic storms. While the most extensive studies have been performed in the Atlantic Region, there have been studies demonstrating ENSO variability in Pacific region tropical cyclone occurrence as well (e.g., Chan, 1985; Wu and Lau, 1992). These studies showed similar results for the Pacific Ocean basin as a whole. However, Ramage and Hori (1981) and Lander (1994) found no ENSO variability in the overall tropical cyclone numbers throughout the North Pacific as a whole, but significant variability in the primary tropical cyclone genesis regions. Since then, studies have shown that the focus of tropical storm activity moves southeastward (northwestward) during El Niño (La Niña) years (e.g., Chan, 1985; Wu and Lau, 1992; Lander, 1994; Wang and Chan, 2002). Thus, this study has three objectives and they are; 1) to develop a detailed long-term climatology of tropical cyclone activity in the SSCS region, 2) to examine the character of the long-term trends and interannual variations in tropical cyclone activity, and 3) to examine variations in the background atmospheric and surface environment in the SSCS (especially in the active season – November and December). To accomplish the second objective, we examined whether or not there were significant ENSO or PDO related variations in the SSCS tropical cyclone climatology. One outcome of this study will be to produce information that may provide useful guidance for the long-range prediction of tropical cyclone occurrence for tropical weather forecasters in the SSCS region (Malaysia and adjacent nations). This will include information for advising policy makers regarding future tropical cyclone occurrences.