Abstract The first successful simulation of tropical cyclone (TC) intensification was achieved with a three-layer model, often named the Ooyama-type three-layer model, which consists of a slab boundary layer and two shallow water layers above. Later studies showed that the use of a slab boundary layer would produce unrealistic boundary layer wind structure and too strong eyewall updraft at the top of TC boundary layer and thus simulate unrealistically rapid intensification compared to the use of a height-parameterized boundary layer. To fully consider the highly height-dependent boundary layer dynamics in the Ooyama-type three-layer model, this study replaced the slab boundary layer with a multilevel boundary layer in the Ooyama-type model and used it to conduct simulations of TC intensification and also compared the simulation with that from the model version with a slab boundary layer. Results show that compared with the simulation with a slab boundary layer, the use of a multilevel boundary layer can greatly improve simulations of the boundary-layer wind structure and the strength and radial location of eyewall updraft, and thus more realistic intensification rate due to better treatments of the surface layer processes and the nonlinear advection terms in the boundary layer. Sensitivity of the simulated TCs to the model configuration and to both horizontal and vertical mixing lengths, sea surface temperature, the Coriolis parameter, and the initial TC vortex structure are also examined. The results demonstrate that this new model can reproduce various sensitivities comparable to those found in previous studies using fully physics models.
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Revisiting the Dynamics of Eyewall Contraction of Tropical Cyclones
The dynamics of eyewall contraction of tropical cyclones (TCs) has been revisited in this study based on both three-dimensional and axisymmetric simulations and dynamical diagnostics. Because eyewall contraction is closely related to the contraction of the radius of maximum wind (RMW), its dynamics is thus often studied by examining the RMW tendency in previous studies. Recently, Kieu and Stern et al. proposed two different frameworks to diagnose the RMW tendency but had different conclusions. In this study, the two frameworks are evaluated first based on theoretical analysis and idealized numerical simulations. It is shown that the framework of Kieu is a special case of the earlier framework of Willoughby et al. if the directional derivative is applied. An extension of Stern et al.’s approach not only can reproduce but also can predict the RMW tendency. A budget of the azimuthal-mean tangential wind tendency indicates that the contributions by radial and vertical advections to the RMW tendency vary with height. Namely, radial advection dominates the RMW contraction in the lower boundary layer, and vertical advection favors the RMW contraction in the upper boundary layer and lower troposphere. In addition to the curvature, the increase of the radial gradient of horizontal mixing (including the resolved eddy mixing in three dimensions) near the eyewall prohibits eyewall contraction in the lower boundary layer. Besides, the vertical mixing including surface friction also plays an important role in the cessation of eyewall contraction in the lower boundary layer.
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- Award ID(s):
- 1834300
- NSF-PAR ID:
- 10132606
- Date Published:
- Journal Name:
- Journal of the Atmospheric Sciences
- Volume:
- 76
- Issue:
- 10
- ISSN:
- 0022-4928
- Page Range / eLocation ID:
- 3229 to 3245
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1175/JAS-D-19-0076.1
