Giant Ocean Waves More
Common Than Thought
August 05, 2005 — By Randolph E. Schmid, Associated Press
WASHINGTON — Last year's Hurricane
Ivan generated an ocean wave that towered higher than 90 feet at one
point, says a study that also suggests such giants may be more common
than once thought.
Research indicates these are not "rogue waves but actually fairly common
during hurricanes," said David Wang of the Naval Research Laboratory at
Stennis Space Center, Miss.
The giant wave was detected 75 miles south of Gulfport, Miss., by
instruments on the ocean floor that measure the pressure of water above
them. Using those readings, scientists can calculate the height of waves
from trough to crest.
Last Sept. 15, as Hurricane Ivan passed through the area, the
instruments measured 146 large waves, including 24 higher than 50 feet
and one at 91 feet, Wang and his colleagues report in Friday's issue of
the journal Science.
The giant wave did not reach land. Unlike a tsunami, which reaches down
to the sea floor, this was a wind wave, generated on the ocean surface
by the powerful forces of the storm.
Because shipping tends to try to avoid hurricanes, many large waves are
unseen by humans, let alone measured.
Scientists at the National Oceanic and Atmospheric Administration have a
different way of calculating wave heights, using buoys at sea.
Hendrik Tolman, an ocean wave expert at the NOAA's Climate Prediction
Center, said a wave such as the giant one measured during Ivan is within
expected limits.
Ocean researchers generally focus on "significant wave height," which is
the average of the highest one-third of waves, he said. Within that
average, there can be a much larger waves.
The highest significant wave height in Ivan was 52 feet as calculated by
the NOAA buoys and 58 feet as calculated by Wang's group.
In a short-lived storm such as Ivan, a maximum wave of twice the
significant height can occur, said Tolman, who was not part of Wang's
research group.
Wang, however, said Ivan's towering wave exceeds those measured in other
infamous storms.
"In 1969, Hurricane Camille produced a 44-foot wave by an oil rig near
the storm's center," he said. "Only two other buoy reports exceed the
52-foot mark set by Ivan, both of which occurred in the North Pacific
where winter storms are larger than hurricanes," Wang said.
With forecasters expecting continued high hurricane activity in the next
few years, this report should be a good starting point to increase
wave-height research, Wang said.
On Tuesday, meteorologists at the National Weather Service increased
their storm forecast for this year. There have already been eight named
storms and they said there could be as many as 11 to 14 more tropical
storms, including seven to nine more hurricanes, by the end of November.
Also, on Monday, Kerry Emmanuel of the Massachusetts Institute of
Technology published a report indicating that global warming is making
hurricanes stronger.
Wang's research was funded by the Office of Naval Research and the
Interior Department's Minerals Management Service, which oversees
offshore oil drilling.
Source: Associated Press |