Low-Frequency Vortex Pair over the Tropical Eastern Indian Ocean and the South China Sea Summer Monsoon Onset

In this paper, the relationship between a pair of low-frequency vortexes over the equatorial Indian Ocean and the South China Sea (SCS) summer monsoon onset is studied based on a multi-year (1980-2003) analysis. A pair of vortexes symmetric about the equator is an important feature prior to the SCS summer monsoon onset. A composite analysis shows that the life cycle of the pair of vortexes is closely associated with the SCS summer monsoon onset. The westerly between the twin cyclones is an important factor to the SCS summer monsoon onset process.