Official Nasa Communication 01-121

David E. Steitz Headquarters, Washington, DC (Phone: 202/358-1730)

June 14, 2001

Gisela Speidel University of Hawaii, Honolulu (Phone: 808/956-9252) RELEASE: 01-121 SATELLITES REVEAL HAWAII'S LONG TAIL OF WIND AND WATER 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. -end-