The potential impacts of warmer-continent-related lower-layer equatorial westerly wind on tropical cyclone initiation |
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Authors: | YUAN Zhuojian QIAN Yu-Kun QI Jindian WU Junjie |
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Institution: | Center for Monsoon and Environmental Research/Department of Atmospheric Science,
Sun Yat-sen University, Guangzhou 510275;Center for Monsoon and Environmental Research/Department of Atmospheric Science,
Sun Yat-sen University, Guangzhou 510275, State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology,
Chinese Academy of Sciences, Guangzhou 510301;Center for Monsoon and Environmental Research/Department of Atmospheric Science,
Sun Yat-sen University, Guangzhou 510275;Civil Aviation Flight University of China, Guanghan 618307 |
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Abstract: | Global climate models predict that the increasing Amazonian-deforestation
rates cause rising temperatures (increases of 1.8oC to 8oC 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 Atlantic 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. |
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Keywords: | tropical cyclone human activities climate change global warming |
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