What is the eye of the storm?

May 3, 2006

This is the question that draws many people to this blog via search engine queries. Until now it has lacked an answer to that question.

The American Meteorological Society glossary offers a brief definition:

eye—In meteorology, usually the “eye of the storm” (hurricane, typhoon), that is, the roughly circular area of comparatively light winds found at the center of a severe tropical cyclone and surrounded by the eyewall. The winds increase gradually outward from the center but can remain very light up to the inner edge of the eyewall. No rain occurs and in intense tropical cyclones the eye is clear with blue sky overhead. Most, but not all, tropical cyclones with maximum winds in excess of 40 m s−1(78 knots) have eyes visible on satellite imagery. Eye diameters vary from 10 to more than 100 km.

In the past two years we have seen the full span of eye diameters. Wilma at peak intensity had an eye 5 miles in diameter, while that of Frances exceeded 60 miles.

The FAQ of NOAA's Hurricane Research Division offers further discussion on what is the eye of a storm.

When one reads the paragraph stating that there is controversy and uncertainty over how exactly eyes form and sees the research cites as being from the early 1980's, one may think that current research has figured it out. Alas, that is not the case. For a technical discussion of the problem see Jonathan Vigh's extended abstract, Formation of the Hurricane Eye (non-technical readers may enjoy the image of an eye taken from a U-2 that is at the end).

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A couple of asides:

     1. When I started this blog, I didn't envision blogging about hurricanes, the name was chosen to symbolize this blog being a place of calmness amidst a (figurative) furious storm.

     2. I slipped a day in posting. In the scheme for the month that I described on Monday, this is a Tuesday post. 

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