Meteorological process around and within the eye of intense tropical cyclones
Concentric eyewalls seen in Typhoon Haima as it travels west across the Pacific Ocean.
In meteorology, eyewall replacement cycles, also called concentric eyewall cycles, naturally occur in intense tropical cyclones, generally with winds greater than 185 km/h (115 mph), or major hurricanes (Category 3 or above). When tropical cyclones reach this intensity, and the eyewall contracts or is already small, some of the outer rainbands may strengthen and organize into a ring of thunderstorms—a new, outer eyewall—that slowly moves inward and robs the original, inner eyewall of its needed moisture and angular momentum. Since the strongest winds are in a tropical cyclone's eyewall, the storm usually weakens during this phase, as the inner wall is "choked" by the outer wall. Eventually the outer eyewall replaces the inner one completely, and the storm may re-intensify.[1]
The discovery of this process was partially responsible for the end of the U.S. government's hurricane modification experiment Project Stormfury. This project set out to seed clouds outside the eyewall, apparently causing a new eyewall to form and weakening the storm. When it was discovered that this was a natural process due to hurricane dynamics, the project was quickly abandoned.[2]
Almost every intense hurricane undergoes at least one of these cycles during its existence. Recent studies have shown that nearly half of all tropical cyclones, and nearly all cyclones with sustained winds over 204 kilometres per hour (127 mph; 110 kn), undergo eyewall replacement cycles.[3] Hurricane Allen in 1980 went through repeated eyewall replacement cycles, fluctuating between Category 5 and Category 4 status on the Saffir-Simpson Hurricane Scale several times. Typhoon June (1975) was the first reported case of triple eyewalls,[4] and Hurricane Juliette and Iris (2001) were documented cases of such.[5][6]
^Sitkowski, Matthew; Kossin, James P.; Rozoff, Christopher M. (2011-06-03). "Intensity and Structure Changes during Hurricane Eyewall Replacement Cycles". Monthly Weather Review. 139 (12): 3829–3847. Bibcode:2011MWRv..139.3829S. doi:10.1175/MWR-D-11-00034.1. ISSN 0027-0644. S2CID 53692452.
^Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. "Frequently Asked Questions: What are "concentric eyewall cycles" (or "eyewall replacement cycles") and why do they cause a hurricane's maximum winds to weaken?". NOAA. Retrieved 2006-12-14.
^Cite error: The named reference willoughby1982 was invoked but never defined (see the help page).
^Shanmin, Chen (1987). "Preliminary analysis on the structure and intensity of concentric double-eye typhoons". Advances in Atmospheric Sciences. 4 (1): 113–118. Bibcode:1987AdAtS...4..113C. doi:10.1007/BF02656667. S2CID 117062369.
^McNoldy, Brian D. (2004). "Triple Eyewall in Hurricane Juliette". Bulletin of the American Meteorological Society. 85 (11): 1663–1666. Bibcode:2004BAMS...85.1663M. doi:10.1175/BAMS-85-11-1663.
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