Interannual and interdecadal variations of tropical cyclone activity in the South China Sea

This study attempts to determine factors that affect tropical cyclone (TC) activities in the South China Sea (SCS). The TC activities in the SCS are analysed and their relationship to different atmospheric phenomena are investigated. These include El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), and the combined effect of both. Results indicate that the total number of TCs and the number entering SCS from WNP (ENT) are less during an El Niño (EN) and more during a La Niña (LN), while the number formed inside the SCS (FORM) is apparently unaffected. Positive (Negative) phase of PDO generally favours less (more) TCs in all categories, while their combined effects have even more extreme effects on TC number. An explanation for this seems to lie in the effects ENSO and PDO have on the factors affecting TC behaviour, which in turn causes conditions in the WNP to become favourable or unfavourable for TC genesis and movement into the SCS. Based on these results, eight factors are chosen for each case (ENT and FORM in early and late seasons) through a stepwise regression technique, and they are very good representation of the actual situations (all with correlation coefficients of > 0.9).