Numerical Experiments Reveal Initial Wind Field Structure as Crucial Factor in Determining Tropical Cyclone Size and Intensity


Tropical cyclones (TCs) are responsible for significant damage to property and human life. The size and intensity of these storms are critical factors in determining the level of destruction they can cause. However, the relationship between a TC's size and intensity during its development phase has been difficult to understand.
Now, a team of researchers led by Professor CHEN Guanghua at the Key Laboratory of Cloud-Precipitation Physics and Severe Storms of the Institute of Atmospheric Physics at the Chinese Academy of Sciences has shed light on this relationship by examining the wind field structure of TCs during their formation.
In a paper published in Advances in Atmospheric Science, the researchers analyzed the relative impacts of two critical parameters - the radius of maximum wind (RMW) and the radial decay of winds outside the RMW - on the degree of size expansion under the same level of intensity increment. 
They found that vortexes with larger RMW and broader wind fields tend to expand more under the same level of intensity increment, highlighting the importance of paying attention to incipient storms with large RMW.
Tropical cyclones Olaf (top) and Nancy (bottom) on February 16, 2005 over South Pacific. (Image courtesy the MODIS Rapid Response Team, NASA-GSFC)
The researchers also discovered that the RMW plays a major role in the size-intensity relationship. Increasing the initial RMW significantly slows down the organization and development of the eyewall convection, leading to slow intensifying. On the other hand, initially broader winds allow for active outer convection and are favorable for size expansion, which can lower wind transports to the inner region and impede intensification when the RMW is large.
"This study is a preliminary attempt to comprehend the physical mechanisms responsible for the variation of size-intensity relationship," said Prof. CHEN. "Further research is ongoing to incorporate more complex internal and external forces."
Understanding the size and intensity relationship of TCs is crucial for estimating their potential destruction to humanity. The findings of this study can help improve our ability to predict and prepare for these devastating natural disasters.
Chen, K. X., G. H. Chen, and D. L. Shi. 2023: Modulation of the wind field structure of initial vortex on the relationship between tropical cyclone size and intensity. Adv. Atmos. Sci.,
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