Better explicating the strengths and shortcomings of these models will help refine projections and improve transparency in the years ahead.
Image credit: Witsawat.S.
Edited by Kerry A. Emanuel, Massachusetts Institute of Technology, Cambridge, MA, and approved September 21, 2020 (received for review June 29, 2020)
Significance
The deep clouds that make up tropical disturbances, the precursors to more intense tropical cyclones (TCs) (including hurricanes and typhoons), effectively trap infrared radiation emitted by Earth’s surface and lower atmosphere. Our results demonstrate that the local atmospheric warming caused by this “cloud greenhouse effect” is a key trigger for promoting and accelerating the evolution of such precursor storms into intense TCs. The forecasting of TC formation remains extremely challenging, while the representation of cloud processes and their feedback with radiation is a large source of uncertainty in the numerical models that forecasts rely upon. Our results suggest that focusing future research on constraining these processes in models holds promise for key progress in the prediction of these devastating storms.
Abstract
The tall clouds that comprise tropical storms, hurricanes, and typhoons—or more generally, tropical cyclones (TCs)—are highly effective at trapping the infrared radiation welling up from the surface. This cloud–infrared radiation feedback, referred to as the “cloud greenhouse effect,” locally warms the lower–middle troposphere relative to a TC’s surroundings through all stages of its life cycle. Here, we show that this effect is essential to promoting and accelerating TC development in the context of two archetypal storms—Super Typhoon Haiyan (2013) and Hurricane Maria (2017). Namely, this feedback strengthens the thermally direct transverse circulation of the developing storm, in turn both promoting saturation within its core and accelerating the spin-up of its surface tangential circulation through angular momentum convergence. This feedback therefore shortens the storm’s gestation period prior to its rapid intensification into a strong hurricane or typhoon. Further research into this subject holds the potential for key progress in TC prediction, which remains a critical societal challenge.
Footnotes
- ↵1To whom correspondence may be addressed. Email: james.ruppert{at}psu.edu.
Author contributions: J.H.R. designed research; J.H.R., A.A.W., X.T., and E.L.D. performed research; J.H.R. analyzed data; and J.H.R. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2013584117/-/DCSupplemental.
Data Availability.
All model and postprocessing code necessary to replicate the results of this study have been archived in a public repository (60) or are cited in the Materials and Methods.
Published under the PNAS license.
References
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The critical role of cloud–infrared radiation feedback in tropical cyclone development
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- Physical Sciences
- Earth, Atmospheric, and Planetary Sciences
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