Features of ocean surface winds observed by the QuikSCAT satellite before tropical cyclogenesis over the South China Sea

Ocean surface winds observed by the Quick Scatterometer (QuikSCAT) satellite prior to the geneses of 36 tropical cy- clones (TCs) in the South China Sea (SCS) are investigated in this paper. The results show that there are areas with negative mean horizontal divergence around the TC genesis locations three days prior to TC formation. The divergence term [-(f ζ)( u/ x v/ y)] in the vorticity equation is calculated based upon the QuikSCAT ocean surface wind data. The calculated mean divergence term is about 10.3 times the mean relative vorticity increase rate around the TC genesis position one day prior to TC genesis, which shows the important contributions of the divergence term to the vorticity increase prior to TC formation. It is suggested that criteria related with the divergence and divergence term be applied in early detections of tropical cyclogenesis using the QuikSCAT satellite data.