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17 Why don't we try to destroy tropical cyclones by: pick one or more - a) seeding them with silver iodide, b) nuking them, c) placing a substance on the ocean surface, d) etc. ?




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

17 Why don't we try to destroy tropical cyclones by: pick one or more - a) seeding them with silver iodide, b) nuking them, c) placing a substance on the ocean surface, d) etc. ?

Actually for a couple decades NOAA and its predecessor tried to
weaken hurricanes by dropping silver iodide - a substance that serves as a
effective ice nuclei - into the rainbands of the storms. The idea was that
the silver iodide would enhance the thunderstorms of the rainband by
causing the supercooled water to freeze, thus liberating the latent heat of
fusion and helping the rainband to grow at the expense of the eyewall.
With a weakened convergence to the eyewall, the strong inner core winds
would also weaken quite a bit. Neat idea, but it, in the end, had a fatal
flaw: there just isn't much supercooled water available in hurricane
convection - the buoyancy is fairly small and the updrafts correspondingly
small compared to the type one would observe in mid-latitude continental
super or multicells. The few times that they did seed and saw a reduction
in intensity was undoubtedly due to what is now called "concentric eyewall
cycles".

Concentric eyewall cycles naturally occur in intense tropical cyclones
(wind > 50 m/s or 100 kt). As tropical cyclones reach this threshold of
intensity, they usually - but not always - have an eyewall and radius of
maximum winds that contracts to a very small size, around 10 to 25 km. At
this point, some of the outer rainbands may organize into an outer ring of
thunderstorms that slowly moves inward and robs the inner eyewall of its
needed moisture and momentum. During this phase, the tropical cyclone
is weakening (i.e. the maximum winds die off a bit and the central
pressure goes up). Eventually the outer eyewall replaces the inner one
completely and the storm can be the same intensity as it was previously
or, in some cases, even stronger. A concentric eyewall cycle occurred
in Hurricane Andrew (1992) before landfall near Miami: a strong intensity
was reached, an outer eyewall formed, this contracted in concert with a
pronounced weakening of the storm, and as the outer eyewall completely
replaced the original one the hurricane reintensified.

Thus nature accomplishes what NOAA had hoped to do artificially. No
wonder that the first few experiments were thought to be successes. To
learn about the STORMFURY project as it was called, read Willoughby et al.
(1985). To learn more about concentric eyewall cycles, read Willoughby et
al. (1982) and Willoughby (1990).

As for the other ideas, there has been some experimental work in
trying to develop a liquid that when placed over the ocean surface would
prevent evaporation from occurring. If this worked in the tropical cyclone
environment, it would probably have a detrimental effect on the intensity
of the storm as it needs huge amounts of oceanic evaporation to continue
to maintain its intensity (Simpson and Simpson 1966). However, finding a
substance that would be able to stay together in the rough seas of a
tropical cyclone proved to be the downfall of this idea.

There was also suggested about 20 years ago (Gray et al. 1976) that
the use of carbon black (or soot) might be a good way to modify tropical
cyclones. The idea was that one could burn a large quantity of a heavy
petroleum to produce vast numbers of carbon black particles that would be
released on the edges of the tropical cyclone in the boundary layer. These
carbon black aerosols would produce a tremendous heat source simply by
absorbing the solar radiation and transferring the heat directly to the
atmosphere. This would provide for the initiation of thunderstorm activity
outside of the tropical cyclone core and, similarly to STORMFURY, weaken the
eyewall convection. This suggestion has never been carried out in real-
life.

Lastly, there always appears ideas during the hurricane season that
one should simply use nuclear weapons to try and destroy the storms. Apart
from the concern that this might not even alter the storm, this approach
neglects the problem that the released radiation would fairly quickly
move with the tradewinds to over land. Needless to say, this is not a
good idea.

< Start Soap Box >

Perhaps the best solution is not to try to alter or destroy the
tropical cyclones, but just learn to co-exist better with them. Since
we know that coastal regions are vulnerable to the storms, enforce building
codes that can have houses stand up to the force of the tropical cyclones.
Also the people that choose to live in these locations should willing to
shoulder a fair portion of the costs in terms of property insurance -
not exorbitant rates, but ones which truly reflect the risk of living in
a vulnerable region.
< End Soap Box >

 

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