The Hawaiian Islands trigger an extraordinary interaction
between wind and ocean that extends thousands of miles. This
island effect is much larger than has ever been observed by
scientists before.

Using data from Earth-observing satellites, researchers
discovered a narrow, eastward-flowing ocean current that
extends nearly 5,000 miles from Asia to Hawaii. While
scientists have known of an eastward current off Asia for some
years, this new research shows such a current could possibly
have aided the islands’ early settlers, thought to have sailed
from the Far East.

The scientists’ report appears in the June 15 issue of the
journal Science.

“Our study shows how tiny islands, barely visible on a world
map, can affect a long stretch of Earth’s largest ocean,” said
Dr. Shang-Ping Xie, University of Hawaii’s International
Pacific Research Center and Meteorology Department, Honolulu.
“The Pacific could only be sketchily observed with ship-based
instruments; advanced satellite technology, however, is
changing all this and giving us fascinating new images of this
ocean.”

“According to conventional theories and observations, the wind
wakes caused by islands should dissipate within approximately
300 kilometers (180 miles) downstream and should not be felt
in the western Pacific,” said Dr. Timothy Liu, NASA’s Jet
Propulsion Laboratory (JPL), Pasadena, CA. “But we were able
to observe a pattern that stretches more than 3,000 kilometers
(1,800 miles) in the atmosphere and the ocean from the western
side of the Hawaiian Islands to beyond Wake Island in the
western Pacific.”

Liu concluded, “This pattern, never recognized before, is a
narrow but long break in the steady Pacific trade winds and
the north equatorial current. It is triggered by the high
Hawaiian Islands and sustained by positive ocean-atmosphere
feedback.”

In their paper, “Far-Reaching Effects of the Hawaiian Islands
on the Pacific Ocean-Atmosphere,” the authors describe a chain
of events that begins when the steady westward trade winds and
north equatorial current encounter the volcanically formed
Hawaiian Islands standing tall in the middle of the Pacific
Ocean. The islands force the winds to split, creating areas of
weak winds behind the islands and strong winds on the islands’
flanks. Individual wakes form behind the islands, but these
merge into a broader wake about 150 miles to the west.

The winds associated with this broader wake spawn a narrow
eastward countercurrent that draws warm water from west to
east. When the winds encounter these warm surface waters, they
rise with convection. Cooler winds move in to feed the rising
air, creating a rotating effect and reinforcing the current.
The current, in turn helps drive the winds, setting up a
positive feedback between ocean and atmosphere that continues
for thousands of kilometers to the west.

The study shows that the surface winds react to sea-surface
temperature variations as small as a few tenths of one degree,
indicating climate sensitivity much higher than has been
previously thought. This new knowledge of ocean-atmosphere
interplay will help improve climate models used to predict
phenomena like El Nino and global warming.

For their paper, Xie and his colleagues used data from NASA’s
QuikScat satellite, the European Remote Sensing satellites and
the U.S.-Japan Tropical Rainfall Measuring Mission (TRMM).

The SeaWinds on QuikScat project is managed for NASA’s Earth
Science Enterprise by JPL. NASA’s Goddard Space Flight Center,
Greenbelt, MD, manages TRMM.