Hurricanes: Their Nature and Impacts on Society - Climate Science ...

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HURRICANES: THEIR NATURE AND IMPACT ON SOCffiTY
Figure 3.9 A model simulation of the eye <strong>and</strong> eye wall region of a mature hurricane.
The contours show wind speed in miles per hour. The solid contours represent winds
moving into the page <strong>and</strong> dashed contours represent winds moving out of the page. The
shaded region illustrates the locations of cloud. Figure provided by Dr Mel Nicholls,
Colorado State University; this work is also reported in Nicholls <strong>and</strong> Pielke (1995)
l<strong>and</strong>fall because of the wann water of the Gulf Stream (Willoughby <strong>and</strong> Black
1996).*
Fortunately, few hurricanes attain their theoretical maximum potential
intensity. The presence of significant vertical wind shear is likely the major
reason that hurricanes do not attain this level of intensity.
* There are several theories on the maximum potential intensity of tropical cyclones (Gray
1997). The heat engine analog of these storms has been used to estimate maximum possible
strength based on inflow <strong>and</strong> outflow temperature differences (Emanuel 1986; 1987). Emanuel et
al. (1995) use this concept to propose that extremely strong hurricanes could develop, which they
call "hypercanes". A different mechanism has also been proposed where hurricane intensity is
limited by controls on deep cumulus cloud buoyancy in the eye wall (Holl<strong>and</strong> 1997). William
Gray of Colorado State University, however, maintains that upper-level momentum export from
the storm, along with surface frictional dissipation must be considered together with the thermodynamic
controls proposed by Emanuel <strong>and</strong> by Holl<strong>and</strong> (Gray 1997).