Journal
JOURNAL OF CLIMATE
Volume 34, Issue 9, Pages 3571-3589Publisher
AMER METEOROLOGICAL SOC
DOI: 10.1175/JCLI-D-20-0387.1
Keywords
North Pacific Ocean; Atmosphere-ocean interaction; Boundary currents; Summer; warm season; Climate variability; Numerical analysis; modeling
Categories
Funding
- JSPS [18K03737]
- MEXT [19H05704]
- Japan Fisheries Research and Education Agency
- NSF [2019312]
- U.S. National Aeronautics and Space Administration [80NSSC19K0058]
- JAMSTEC IPRC Collaborative Research (JICore)
- Grants-in-Aid for Scientific Research [19H05704, 18K03737] Funding Source: KAKEN
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The Kanto district in Japan, including Tokyo, with a population of 40 million, experiences hot and humid summers. The recent large meander path of the Kuroshio off the southern coast has led to coastal warming and increased water vapor, resulting in surface warming and more discomfort days in the region during LM years. These findings have significant impacts on summer climate in Japan and could improve weather and seasonal climate forecasts in the region.
The Kanto district in Japan, including Tokyo, has 40 million inhabitants and its summer climate is characterized by high temperature and humidity. The Kuroshio that flows off the southern coast of the Kanto district has taken a large meander (LM) path since the summer of 2017 for the first time since the 2004-05 event. Recently developed satellite observations detected marked coastal warming off the Kanto-Tokai district during the LM path period. By conducting regional atmospheric model experiments, it is found that summertime coastal warming increases water vapor in the low-level atmosphere through enhanced evaporation from the ocean and influences near-surface winds via the vertical mixing effect over the warming area. These two changes induce an increase in water vapor in Kanto district, leading to an increase in downward longwave radiation at the surface and then surface warming through a local greenhouse effect. As a result, summer in Kanto district becomes increasingly hot and humid in LM years, with double the number of discomfort days compared with non-LM years. Our simulations and supplementary observational studies reveal the significant impacts of the LM-induced coastal warming on the summertime climate in Japan, which can exceed previously identified atmospheric teleconnections and climate patterns. Our results could improve weather and seasonal climate forecasts in this region.
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