How much energy does a hurricane release? |
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A hurricane is a heat engine; obtaining its heat input from the warm,
humid air over the tropical ocean, and releasing this heat through the
condensation of water vapor into water droplets in deep thunderstorms of
the eyewall and rainbands, then giving off a cold exhaust in the upper
levels of the troposphere. One can look at the energetics of a hurricane
in two ways:
- The total amount of energy released by the condensation of water droplets
- The amount of kinetic energy generated to maintain the strong swirling
winds of the hurricane (Emanuel 1999).
It turns out that the vast majority of the heat released in the condensation
process is used to cause rising motions in the thunderstorms and only a
small portion drives the storm's horizontal winds.
Method 1 - Total energy released through cloud/rain formation:
An average hurricane produces 1.5 cm/day (0.6 inches/day) of rain inside
a circle of radius 665 km (360 n.mi) (Gray 1981). More rain falls in the
inner portion of hurricane around the eyewall, less in the outer rainbands.
Converting this to a volume of rain gives 2.1 x 1016 cm3/day. A cubic cm
of rain weighs 1 gm. Using the latent heat of condensation, this amount
of rain produced gives 5.2 x 1019 Joules/day or 6.0 x 1014 Watts. This
is equivalent to 200 times the world-wide electrical generating capacity
- an incredible amount of energy produced!
Method 2 - Total kinetic energy (wind energy) generated:
For a mature hurricane, the amount of kinetic energy generated is equal
to that being dissipated due to friction. The dissipation rate per unit
area is air density times the drag coefficient times the windspeed cubed
(See Emanuel 1999 for details). One could either integrate a typical wind
profile over a range of radii from the hurricane's center to the outer
radius encompassing the storm, or assume an average windspeed for the inner
core of the hurricane. Doing the latter and using 40 m/s (90 mph) winds
on a scale of radius 60 km (40 n.mi.), one gets a wind dissipation rate
(wind generation rate) of 1.5 x 1012 Watts. This is equivalent to about
half the world-wide electrical generating capacity - also an amazing amount
of energy being produced!
Either method is an enormous amount of energy being generated by hurricanes.
However, one can see that the amount of energy released in a hurricane
(by creating clouds/rain) that actually goes to maintaining the hurricane's
spiraling winds is a huge ratio of 400 to 1.
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