No one has ever described a wind wake this big before.
Consequently, "The biggest challenge is that there was no road map for our study,"
said Shang-Ping Xie at the University of Hawaii. "Nobody has ever seen such
a long wake and made it a scientific problem."
Discovering this wind wake serves as a roadmap for future
areas of research such as climate modeling, according to Xie, who led the international
research team from the U.S., China, and Japan. "Whether and how the atmosphere
responds to sea surface temperature changes in the subtropics is a key issue,"
he said. Such information could help explain how the atmosphere and ocean feed
into each other to create a looping effect, and "concerns all practicing climate
The wind wake is part of a positive "feedback loop" sustained
by the jutting height of the major Hawaiian Islands, which interrupt trade winds
that blow toward the southwest. The islands split the trade winds in two—the
stronger winds on the flanks of the islands, and the weaker winds in the leeward
side, behind the islands. An eastward ocean current generates a long band of
warm water that travels from Asia straight to Hawaii, where the winds converge,
keeping the wind wake going again for almost 2000 miles. This reaches as far
out west as the Marshall Islands, halfway between Hawaii and Papua New Guinea.
"A unique confluence of factors produces this exceptional
wake," said H. Jesse Smith, Associate Editor at Science. "It is particularly
interesting because the effects of meteorology, topography and ocean circulation
can be seen to interact dynamically in creating this incredibly long wake leeward
of the Hawaiian Islands."
The air-water interactions fostered by the split trade
winds help explain an unusual eastward ocean current in the western North Pacific
Ocean. It's something that puzzled Japanese scientists from the University of
Tokyo in the 1960s because in the Asian end of the Pacific Ocean, westward currents
Now, after analyzing cloud water, sea temperature and wind
speed from satellites such as the NASA QuickSCAT satellite, Xie and colleagues
discovered that one of the currents in question extends approximately 5000 miles
long. "It's like an elephant. Before, we could only see the head and tail,"
said W. Timothy Liu at the California Institute of Technology. "Now, we can
see the whole thing," he continued.
"This high space-time resolution satellite data set was
a dream project for investigating the effects of Hawaii on surface winds. It
became immediately clear that the long tail of the Hawaiian wake could not be
explained by aerodynamic theories," Xie said. Instead, wind variation, or the
sustained stretch of differently blowing small winds, was the reason.
Before the satellite era, there was simply no way to observe
the vast Pacific Ocean with adequate space-time coverage, Xie said. He added,
"On a map of the Pacific Ocean, the tiny Hawaiian Islands are hardly noticeable.
It would thus be a surprise for many people that such tiny islands can have
far-reaching effects on a significant portion of this large ocean."