Abstract
Tropical cyclone (TC) wind structure is important for its intensity change and induced damage, but its modulating factors remain to be explored. A heat-engine-based surface wind structure parameter α, reflecting TC’s relative compactness, is introduced and derived based on an entropy budget framework. We found that α is modulated by three key parameters: the thermodynamic efficiency ϵPI in potential intensity theory, the Carnot efficiency ϵC of the system, and the degree of irreversibility αirr of the system. A higher αirr contributes to a larger α and a lower heat engine efficiency. An expression linking TC intensity and compactness also emerges under this framework. Idealized simulations of a typical moist TC (CTL), a dry (DRY) TC, and a moist reversible TC (REV; in which hydrometeors do not fall out) evinced that the significantly higher αirr in CTL, due to irreversible entropy productions from precipitation dissipation, water vapor diffusion, and irreversible phase changes, contributes to its much larger compactness compared to DRY and REV. The study illustrates the importance of irreversible entropy production processes in modulating TC surface wind field. Simple estimate suggests that α will increase due to a hypothesized increased αirr with warming because of increased water content. This indicates that TCs will become more compact in a warmer climate.
Supplemental information related to this paper is available at the Journals Online website: https://doi.org/10.1175/JAS-D-20-0192.s1.
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