How Does Tropical Cyclone Size Affect the Onset Timing of Secondary Eyewall Formation?
By using idealized numerical simulations, the impact of tropical cyclone size on secondary eyewall formation (SEF) is examined. Both unbalanced boundary layer and balanced processes are examined to reveal the underlying mechanism. The results show that a tropical cyclone (TC) with a larger initial size favors a quicker SEF and a larger outer eyewall. For a TC with a larger initial size, it will lead to a stronger surface entropy flux, and thus more active outer convection. Meanwhile, a greater inertial stability helps the conversion from diabatic heating to kinetic energy. Furthermore, the progressively broadening of the tangential wind field will induce significant boundary layer imbalances. This unbalanced boundary layer process results in a supergradient wind zone that acts as an important mechanism for triggering and maintaining deep convection. In short, different behaviors of balanced and unbalanced processes associated with the initial wind profile lead to different development rates of the secondary eyewall.
Keywordssecondary eyewall formation tropical cyclone size surface entropy flux
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- Huang, Y.-H., M. T. Montgomery, and C.-C. Wu, 2012: Concentric eyewall formation in Typhoon Sinlaku (2008). Part II: Axisymmetric dynamical processes. J. Atmos. Sci., 69, 662–674, doi: 10.1175/JAS-D-11-0114.1.Google Scholar
- Zhou, X. Q., and B. Wang, 2013: Large-scale influences on secondary eyewall size. J. Geophys. Res., 118, 11088–11097, doi: 10.1002/jgrd.50605.Google Scholar
- Zhu, Z. D., and P. Zhu, 2014: The role of outer rainband convection in governing the eyewall replacement cycle in numerical simulations of tropical cyclones. J. Geophys. Res., 119, 8049–8072, doi: 10.1002/2014JD021899.Google Scholar