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From: R. A. Hettinga (no email)
Date: Sat Mar 18 2006 - 19:03:48 EST
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Date: Sat, 18 Mar 2006 19:01:26 -0500
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From: "R. A. Hettinga" <>
Subject: [Clips] Ship endures record-breaking waves
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<http://www.nature.com/news/2006/060313/pf/060313-15_pf.html>
Nature
Published online: 17 March 2006; | doi:10.1038/news060313-15
Ship endures record-breaking waves
Storm shows extreme seas may be more common than thought.
Philip Ball
On the dark and stormy night of 8 February 2000, you wouldn't want to have
been on board the Discovery, a British oceanographic research ship.
Out in the North Atlantic, 250 km west of Scotland and close to the tiny
island of Rockall, the ship was forced to sit through what researchers
think are the biggest waves ever directly recorded in the open ocean. The
two largest measured just over 29 metres from peak to trough - about the
height of a ten-storey building.
The tempest, which hit its peak close to midnight, was terrifying for the
scientists on board. "It was pretty horrendous," says oceanographer Naomi
Holliday of the University of Southampton in England, who was on the
Discovery. "Nobody got any sleep - we were literally thrown out of our
bunks." But the ordeal may have an important scientific payoff in showing
that such extreme ocean conditions could be more common in this area than
previously recognized, say Holliday and colleagues in a paper in
Geophysical Research Letters1.
Marine engineers are keen to know what the ocean is likely to throw at
them. Ships can usually steer clear of big storms, but offshore oil rigs
and exploration platforms would have to be capable of withstanding them.
Ships and oil rigs are typically designed on the assumption that they will
face waves no bigger than around 15 metres.
A computer weather model used by Holliday's team was able to predict the
high seas of 8 February. But it underestimated the height of the waves,
they write.
Freak waves
Gigantic 'freak waves' have been recorded anecdotally in the past, and have
been blamed for the mysterious disappearances of ships at sea. In March
2001 the Caledonian Star passenger ship was hit by a wave in the South
Atlantic estimated to be around 30 m high, which smashed over the vessel
and almost sank it. The QE2 is also said to have met such giants in the
North Atlantic in 1995.
But these so-called rogue waves are thought to be rare anomalies. The
monstrous waves measured by Holliday and her colleagues on the Discovery,
on the other hand, do not seem to have been lone freaks - they were
representative of the storm as a whole, which generated waves typically
more than 18 m high.
The Rockall region is known for its rough seas, the researchers say - a
26-m wave was recorded there in 1972. "Very strong winds are common here
all the year round," says Holliday.
She and her colleagues think that the extreme conditions in 2000 were
caused by a resonance effect, when the high wind speed happened to match
the speed of the waves. This meant that "the wind was continually putting
energy into the sea", says Holliday - like a person running behind another
runner and pushing him along. The researchers suspect that other such cases
of resonant wave growth may have gone unrecorded in this area.
Measuring stick
Higher waves can be whipped up during extreme events such as hurricanes.
Waves around 30 m high are thought to have occurred in the Gulf of Mexico
during Hurricane Ivan in 2004, for example.
But no one was out and about measuring those waves in a boat. Instead, wave
heights were estimated based on measurements of water pressure made by
sensors on the sea floor2.
The monsters seen by Holliday and colleagues may be the largest observed
directly from shipboard measurements. The ship itself acted as the
measuring device: onboard instruments that measure the vessel's
acceleration and the pressure exerted on it were used to determine the size
of the waves throwing it around.
References
1. Holliday N. P., et al. Geophys. Res. Lett., 33 , L05613. (2006).
2. Wang D., et al. Science, 309 . 896
(2005). | Article | PubMed | ChemPort |
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R. A. Hettinga <mailto: >
The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'
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