As the intensity and frequency of the strongest cyclones east of Taiwan have increased, so has the strength of the Kuroshio current, a Pacific current responsible for redistributing heat throughout the western North Pacific Ocean. According to a new study, intensifying tropical cyclones have increased the amount of energy in the ocean eddies that feed into the Kuroshio, accelerating the current. The results reveal a positive feedback between tropical cyclones (TCs) and potentially significant increased warming at higher latitudes. Climate models that overlook this and similar mechanisms may misrepresent the magnitude and pattern of warming in future climate predictions, say the authors. Similar to the Atlantic's Gulf Stream, the Kuroshio current is responsible for transporting vast amounts of warm water from the tropics to higher latitudes, retributing tropical heat to cooler latitudes. The speed of the Kuroshio (and the rate of heat transfer) is largely controlled by the wind and the mesoscale ocean eddies that feed into the larger current. Here, Yu Zhang and colleagues show that the increasing frequency and intensity of TCs in the region - a product of Pacific warming - has had the overall effect of increasing the strength of cyclonic mesoscale ocean eddies that feed the Kuroshio. At the same time, it has decreased the strength of anticyclonic ones. The result is a northward acceleration of the current, resulting in the transfer of more heat energy into the mid- and high-latitude ocean water. The results illustrate how larger tropical cyclones related to increased climate warming can influence large-scale ocean circulation by modifying underlying eddy fields that feed currents - further enhancing climate warming in regions farther afield. "For a proper representation of eddies in climate models, more theoretical and modeling studies are needed to improve our understanding of the physical processes involved in the interactions among eddies, TCs and large-scale ocean circulation, write Zhang et al.
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Science