资源环境科技发展态势分析平台

This study investigates the impact of the south Indian Ocean Dipole (SIOD) on the frequency of tropical cyclones (TCs) over the South China Sea (SCS) in summer (May-August) and winter (September-December) for 1975-2012. The frequency of TCs over the SCS shows significant inter-annual variations in the two seasons and relatively obvious inter-decadal variability in summer. A prominent relationship occurs between the TC generation over the SCS and the SIOD, and the latter can be regarded as a good predictor of the former on inter-annual scale. In winter, vertical circulation is obvious due to a strong SIOD induces intensified ascending motions and high sea surface temperature over the northern SCS with sufficient moisture that supplies a favourable environment for TC formation. The impact of SIOD is weaker in summer but a convergent zone with upwards motion also can be found over northeastern SCS. In addition, the SIOD and El Nino-Southern Oscillation are two primary impacting factors in winter and TC numbers increase when La Nina and positive SIOD events occur simultaneously. However, the SIOD is a dominant and independent impacting factor in summer and El Nino events just play a secondary role.