The potential impacts of warmer-continent-related lower-layer equatorial westerly wind on tropical cyclone initiation

Global climate models predict that the increasing Amazonian-deforestationrates cause rising temperatures (increases of 1.8^oC to 8^oC underdifferent conditions) and Amazonian drying over the 21st century.Observations in the 20th century also show that over the warmer continentand the nearby western South Atlantic Ocean, the lower-layer equatorialwesterly wind (LLEWW) strengthens with the initiation of tropical cyclones(TCs). The warmer-continent-related LLEWW can result from theCoriolis-force-induced deflection of the cross-equatorial flow (similar tothe well-known heat-island effect on sea breeze) driven by the enhancedland-sea contrast between the warmer urbanized continents and relativelycold oceans. This study focuses on the processes relating thewarmer-continent-related LLEWW to the TC initiation and demonstrates thatthe LLEWW embedded in trade easterlies can directly initiate TCs by creatingcyclonic wind shears and forming the intertropical convergence zone. Inaddition to this direct effect, the LLEWW combined with the rotating Earthcan boost additional updraft vapor over the high sea-surface temperatureregion (factor 1), facilitating a surface-to-midtroposphere moist layer(factor 2) and convective instability (factor 3) followed by diabaticprocesses. According to previous studies, the diabatic heating in a finiteequatorial region also activates TCs (factor 4) on each side of the Equatorwith weak vertical shear (factor 5). Factors 1--5 are favorable conditionsfor the initiation of severe TCs. Statistical analyses show that theearliest signal of sustained LLEWW not only leads the earliest signal ofsustained tropical depression by >3 days but also explains a higherpercentage of total variance.