Global climate models predict that the increasing Amazonian-deforestation rates cause rising tempera- tures (increases of 1.8℃ to 8℃ under different conditions) and Amazonian drying over the 21st century. Observations in the 20th century also show that over the warmer continent and the nearby western South At- lantic Ocean, the lower-layer equatorial westerly wind (LLEWW) strengthens with the initiation of tropical cyclones (TCs). The warmer-continent-related LLEWW can result from the Coriolis-force-induced deflection of the cross-equatorial flow (similar to the well-known heat-island effect on sea breeze) driven by the enhanced land-sea contrast between the warmer urbanized continents and relatively cold oceans. This study focuses on the processes relating the warmer-continent-related LLEWW to the TC initiation and demonstrates that the LLEWW embedded in trade easterlies can directly initiate TCs by creating cyclonic wind shears and forming the intertropical convergence zone. In addition to this direct effect, the LLEWW combined with the rotating Earth can boost additional updraft vapor over the high sea-surface temperature region (factor 1), facilitating a surface-to-midtroposphere moist layer (factor 2) and convective instability (factor 3) followed by diabatic processes. According to previous studies, the diabatic heating in a finite equatorial region also activates TCs (factor 4) on each side of the Equator with weak vertical shear (factor 5). Factors 1-5 are favorable conditions for the initiation of severe TCs. Statistical analyses show that the earliest signal of sustained LLEWW not only leads the earliest signal of sustained tropical depression by >3 days but also explains a higher percentage of total variance.
The increase in southern China summer rainfall around 1993 was accompanied by an increase in tropical cyclones that formed in the South China Sea.This study documents the connection of these two features.Our analysis shows that the contribution of tropical cyclones that formed in the South China Sea to southern China summer rainfall experienced a significant increase around 1993,in particular,along the coast and in the heavy rain category.The number of tropical cyclones that formed in the western North Pacific and entered the South China Sea decreased,and their contribution to summer rainfall was reduced in eastern part of southern China(but statistically insignificant).The increase in tropical cyclone-induced rainfall contributed up to ～ 30% of the total rainfall increase along the coastal regions.The increase of tropical cyclones in the South China Sea appears to be related to an increase in local sea surface temperature.
