Florida
Foreclosures
|
Hurricane Ivan,
which struck U.S. shores September 15, 2004, kicked up the
tallest, most extreme waves ever measured, scientists announced.
At more than 90 feet (27 meters) tall from crest to trough and
600 feet (183 meters) long, the massive waves would "wipe out" a
commercial fishing boat, said Douglas Mitchell. Mitchell is an
oceanographer with the U.S. Naval Research Laboratory at the
Stennis Space Center in Mississippi. The researchers estimated
the wave heights using water pressure data from undersea sensors
that had been placed in the Gulf of Mexico for a separate
project. "Have you seen The Perfect Storm?" Mitchell said when
asked to describe the extreme waves. The reference is to the
Hollywood movie based on Sebastian Junger's best-selling book
about an October 1991 storm in the Atlantic Ocean. In the movie,
waves the size of ten-story buildings swamp a 70-foot long-liner
(a type of fishing boat) and its six-person crew. Mitchell and
Naval Research Laboratory colleagues David Wang, William Teague,
Ewa Jarosz, and Mark Hulbert reported their findings in the
journal Science.
The tallest measured wave was 91 feet (28 meters). The
researchers believe they likely missed even larger waves because
their sensors shut down before the most powerful region of the
storm passed over them. "If we had been fortunate enough to
sample the waves when peak winds were overhead, we'd expect to
have seen waves in excess of 130 feet [40 meters] from crest to
trough," team member William Teague said. At its peak intensity,
the hurricane was a Category Five storm—the most powerful—with
sustained winds of 161 miles an hour (259 kilometers an hour).
Hurricane Ivan tore a deadly path across the Caribbean and Gulf
of Mexico in 2004. It struck the Gulf Coast on September 15 with
130 mile an hour (209 kilometer an hour) winds and was directly
resposible for 92 deaths. But the extreme waves disintegrated in
the choppy waters of the Gulf of Mexico, never making landfall.
Extreme Waves
The Naval Research Laboratory team obtained their wave
measurements when Ivan passed directly over a series of six
concrete-ringed instrument packages deployed on the ocean floor
about 75 miles (121 kilometers) south of Gulfport, Mississippi.
Scientists call these moorings "barnys" because they are shaped
like barnacles. The barnys, which sat at depths between 196 and
295 feet (60 and 90 meters), collect current and water pressure
data. They were placed in the gulf for a six-month-long project
to form a comprehensive profile of the region's currents,
Mitchell said. The timing and passage of the hurricane directly
over the sensors was a fortuitous coincidence, Teague said.
An added bonus is that all the instruments survived the storm.
The scientists calculated the wave heights from the changes in
water pressure recorded by the sensors as waves passed overhead.
"As waves go by, the pressure rises and falls," Teague said. To
last for the six-month ocean current project, the barnys'
batteries were designed to turn on for 8.5 minutes every 8
hours—long enough to record the passage of about 50 waves. Even
though the barnys' operational time was staggered, none of the
sensors were on when the strongest part of Ivan passed overhead.
Wave Science
Scientists know little about the biggest ocean waves because
most attempts to measure them have failed. For example,
wave-measuring equipment attached to oil-drilling platforms
often snaps off before a storm peaks. Prior to Ivan, computer
models of wave formation during a hurricane suggested that
monster waves topping 90 feet (27 meters) tall were rare. Thanks
to the fortuitous placement of the barnys, this assumption is
beginning to change. "The implication is waves generated by
hurricanes are much larger than previously suspected.
Waves in excess of 90 feet aren't rogue but are fairly common
during hurricanes," Teague said. According to team member David
Wang, these insights will allow scientists to create better
computer models of hurricane impacts. Such models, for example,
could prompt engineers to build sturdier oil-drilling platforms.
"The models can only be as good as the data provided," Wang
said. "And we always want more [data]. There's more to be
learned about how waves do form under hurricanes."
http://news.nationalgeographic.com/news/2005/08/0804_050804_extremewave.html |
Florida Condo Rentals
|
