Scientists studying satellite data have discovered the world's longest wake of wind, trailing westward some 3,000 kilometers behind the Hawaiian Islands (see image). Though small in size, the islands apparently exert considerable influence over a sizable stretch of the Pacific Ocean. The new research, reported in the current issue of the journal Science, describes how.
Situated in the path of tradewinds from the northwest, the Hawaiian Islands force the air flow to split, flowing around the islands such that the winds in their lee flow weakly, while the flanking winds are fairly strong. These effects are reflected in the ocean surface, which is generally smooth underneath the weak winds of the wake and rough under the strong winds outside the wake. Each island has its own wake, which dissipates fairly quickly. About 300 kilometers downwind, however, a single, broad wake takes their place.
To uncover the mechanisms that sustain this wake over such a great distance, University of Hawaii researcher Shang-Ping Xie and his colleagues consulted observations of winds, clouds and sea surface temperature (SST) from the Tropical Rain Measuring Mission satellite. A complex chain of interaction among these three factors, the team determined, forms the feedback system that generates the Hawaiian wake.
In addition to explaining the lengthy wake, the new work may have broader significance. "Our results demonstrate that surface winds react to modest subtropical SST variations as small as a few tenths of a degree," the authors write. "The simulation of the far-reaching effects of Hawaii can serve as a test for the next generation of high-resolution climate models."