Research Article

Strengthening of the Kuroshio current by intensifying tropical cyclones

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Science  29 May 2020:
Vol. 368, Issue 6494, pp. 988-993
DOI: 10.1126/science.aax5758

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Changing forces in midstream

The intensity and frequency of the strongest cyclones east of Taiwan have increased over the past several decades as the climate has warmed. Zhang et al. found that one result of this trend has been the strengthening of Kuroshio current transport off the coast of Japan. The Kuroshio, like its Atlantic counterpart the Gulf Stream, is a surface current that moves huge volumes of warm water from low latitudes to high ones. As strong Pacific cyclones have become stronger, they have increased the amount of energy contained in cyclonic mesoscale ocean eddies and decreased that of anticyclonic ones. This in turn has increased the transfer of energy to the Kuroshio as eddies move into the current, providing a feedback between climate warming and ocean heat transport.

Science, this issue p. 988

Abstract

A positive feedback mechanism between tropical cyclones (TCs) and climate warming can be seen by examining TC-induced energy and potential vorticity (PV) changes of oceanic geostrophic eddies. We found that substantial dissipation of eddies, with a strong bias toward dissipation of anticyclonic eddies, is directly linked to TC activity. East of Taiwan, where TCs show a remarkable intensifying trend in recent decades, the ocean exhibits a corresponding upward trend of positive PV anomalies. Carried westward by eddies, increasing numbers of positive PV anomalies impinge on the Kuroshio current, causing the mean current to accelerate downstream. This acts in opposition to decreasing basin-scale wind stress and has a potentially important warming impact on the extratropical ocean and climate.

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