Forty million people living in the Kanto region of Japan, which includes Tokyo, may be able to blame a meandering ocean current for increasing hot and humid summers, according to an analysis conducted by an international team of researchers. The Kuroshio Current flows north, bringing warm water from the tropics to Japan's southern coast. Since 2017, however, it has meandered off its traditional path, turning south before continuing north again. Now, scientists have found that the "large meander" is responsible for the uptick in humidity and temperature.

The researchers, from Tohoku University in Japan and the University of Hawaii in the United States, published their results online on Feb. 1 in the Journal of Climate, a journal of the American Meteorological Society.

"In recent years, it has become clear that the ocean influences climate," said first author Shusaku Sugimoto, associate professor of geophysics in the Graduate School of Science at Tohoku University. "Our study shows that the Kuroshio influences the regional climate - especially through the greenhouse effect of water vapor, contributing to significantly warmer temperatures."

The researchers used satellite data from the National Aeronautics and Space Administration (NASA), as well as data from the Automated Meteorological Data Acquisition System stations operated by the Japan Meteorological Agency, to examine 18 summers since 2003.

The last large meander occurred for a year from 2004 to 2005 before starting again in 2017. Controlling for other climatic events, such as storms, and considering global warming trends, the researchers assessed the differences in summers during typical summers and summers during which Kuroshio's path took a large meander.

A Kuroshio meander causes an increase in water temperature/evaporation which is then is then blown towards Kanto by summer south winds. The greenhouse effect of water vapor then causes an increase in the air temperature as illustrated above. ©Tohoku University

Publication Details:
Title: Local atmospheric response to the Kuroshio large meander path in summer and its remote influence on the climate of Japan
Authors: Shusaku Sugimoto, Bo Qiu, and Niklas Schneider
Journal: Journal of Climate
DOI: 10.1175/JCLI-D-20-0387.1

Contact:
Shusaku Sugimoto
Department of Geophysics, Graduate School of Science, Tohoku University
Email: shusaku.sugimoto.d7 * grp.tohoku.ac.jp
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