Questions 43-52 are based on the following
Some of the largest ocean waves in the world are
nearly impossible to see. Unlike other large waves,
these rollers, called internal waves, do not ride the
ocean surface. Instead, they move underwater ,
undetectable without the use of satellite imagery or
sophisticated monitoring equipment. Despite their
hidden nature, internal waves are fundamental parts
of ocean water dynamics, transferring heat to the
ocean depths and bringing up cold water from below.
And they can reach staggering heights-some as tall
Because these waves are involved in ocean mixing
and thus the transfer of heat, understanding them is
crucial to global climate modeling, says Tom
Peacock, a researcher at the Massachusetts Institute
of Technology. Most models fail to take internal
waves into account ." If we want to have more and
more accurate climate models, we have to be able to
capture processes such as this, "Peacock says.
Peacock and his colleagues tried to do just that.
Their study, published in November in Geophysical
Research Letters, focused on internal waves generated
in the Luzon Strait, which separates Taiwan and the
Philippines. Internal waves in this region, thought to
be some of the largest in the world, can reach about
500 meters high. "That` s the same height as the
Freedom Tower that`s just been built in New York,"
Although scientists knew of this phenomenon in
the South China Sea and beyond, they didn`t know
exactly how internal waves formed. To find out,
Peacock and a team of researchers from M.I.T. and
Woods Hole Oceanographic Institution worked with
France`s National Center for Scientific Research
using a giant facility there called the Coriolis
Platform. The rotating platform, about 15 meters
(49.2feet) in diameter, turns at variable speeds and
can simulate Earth`s rotation. It also has walls, which
means scientists can fill it with water and create
accurate, large-scale simulations of various
Peacock and his team built a carbon-fiber resin
scale model of the Luzon Strait, including the islands
and surrounding ocean floor topography. Then they
filled the platform with water of varying salinity to
replicate the different densities found at the strait,
with denser, saltier water below and lighter, less
briny water above. Small particles were added to the
solution and illuminated with lights from below in
order to track how the liquid moved. Finally, they
re-created tides using two large plungers to see how
the internal waves themselves formed.
The Luzon Strait`s underwater topography, with a
distinct double-ridge shape, turns out to be
responsible for generating the underwater waves.
As the tide rises and falls and water moves through
the strait, colder, denser water is pushed up over the
ridges into warmer, less dense layers above it.
This action results in bumps of colder water trailed
by warmer water that generate an internal wave.
As these waves move toward land, they become
steeper-much the same way waves at the beach
become taller before they hit the shore -until they
break on a continental shelf.
The researchers were also able to devise a
mathematical model that describes the movement
and formation of these waves. Whereas the model is
specific to the Luzon Strait, it can still help
researchers understand how internal waves are
generated in other places around the world.
Eventually, this information will be incorporated into
global climate models, making them more accurate.
"It`s very clear, within the context of these [global
climate] models, that internal waves play a role in
driving ocean circulations ," Peacock says.