Graduate Thesis Or Dissertation


Numerical Modeling Study of the Effects of Vertical Wind Shear on Tropical Cyclogenesis Public Deposited

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  • It is well known that vertical wind shear is detrimental for tropical cyclogenesis, however, climatological studies indicate that a small amount of wind shear is most favorable for genesis. Uncertainty still exists as to the degree to which wind shear benefits or inhibits genesis. Thus, we conduct numerical modeling simulations of the development of an idealized initial vortex, representing the circulation of a weak tropical disturbance, in the presence of easterly wind shears from 0 to 5 m s-1 to further understanding of the impacts of vertical wind shear on tropical cyclogenesis. Results show that greater wind shear leads to faster development at early times, but is followed by a longer hiatus period, which eventually leads to a later genesis. The 1 m s-1 and 2 m s-1 wind shear simulations reach genesis most quickly because they take advantage of both a relatively faster early development compared to the no shear simulation and an absence of a hiatus period compared to the simulations with greater wind shear. At early times, without wind shear, downdrafts of symmetrically developed convection form a closed annulus area of cold pools. New convective cells are initiated at the edge of the cold pools leading to an inward and outward propagation of rings of convection, which eventually eliminates the first round of convection at the circulation center. The asymmetry induced by vertical wind shear not only avoids the elimination of convection, but also forms a “snail” structure through merging of cold pools that promotes the formation of strong clustered deep convection. As convection develops, greater shear produces stronger and larger convective-scale downdrafts and causes deeper ventilation, which transports warm and dry air into the lower atmosphere leading to a relatively deep unsaturated layer, resulting in increased boundary layer CIN that inhibits the subsequent development of convection. Continuous deep convection is found essential for alignment of the low-level and mid-level circulations. The period lacking convection interrupts the alignment process, and results in repeated tilt and alignment cycles, which inhibits the strengthening of the system. The findings of this research may contribute to improve forecasting of hurricane formation.

Date Issued
  • 2021-07-26
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  • 2022-12-13
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