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15 Doesn't the friction over land kill tropical cyclones?




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This article is from the Storms FAQ, by Chris Landsea landsea@aoml.noaa.gov with numerous contributions by others.

15 Doesn't the friction over land kill tropical cyclones?

(Parts of this section are written by Sim Aberson.)

No. During landfall, the increased friction over land acts -
somewhat contradictory - to both decrease the sustained winds and also
to increase the gusts felt at the surface (Powell and Houston 1996).
The sustained (1 min or longer average) winds are reduced because of
the dampening effect of larger roughness over land (i.e. bushes, trees
and houses over land versus a relatively smooth ocean). The gusts are
stronger because turbulence increases and acts to bring faster winds
down to the surface in short (a few seconds) bursts.

However, after just a few hours, a tropical cyclone over land will
begin to weaken rapidly - not because of friction - but because the storm
lacks the the moisture and heat sources that the ocean provided. This
depletion of moisture and heat hurts the tropical cyclone's ability to
produce thunderstorms near the storm center. Without this convection,
the storm rapidly fills.

An early numerical simulation (Tuleya and Kurihara 1978) had shown
that a hurricane making landfall over a very moist region (i.e. mainly
swamp) so that surface evaporation is unchanged, intensification may
result. However, a more recent study (Tuleya 1994) that has a more
realistic treatment of surface conditions found that even over a swampy
area a hurricane would weaken because of limited heat sources. Indeed,
nature conducted this experiment during Andrew as the hurricane
traversed the very wet Everglades, Big Cypress and Corkscrew Swamp areas
of southwest Florida. Andrew weakened dramatically: peak winds
decreased about 33% and the sea level pressure in the eye filled 19 mb
(Powell and Houston 1996).

 

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