Habitable Japan Sustainability of atmospheric and oceanic environment as a survival basis of island country Japan Grant-in-Aid for Transformative Research Areas (A) (2024–2028)

Extreme heat in Japan in summer 2023 is still fresh in our memory. It was caused by global warming, meandering westerlies, and unusually high seawater temperature. Since one year ago, marine heat waves have existed over the Pacific Ocean off Tohoku with a temperature 5-6ºC higher than the average year, due mainly to the northward shift of the Kuroshio Extension. On the other hand, the Oyashio, which brings colder water from the north, has retreated greatly to the north since mid-2010s. The Japan Sea was also anomalously warm in summer 2023, while the Kuroshio south of Japan has taken a large-meander path since 2017 for the longest period observed. Together with ocean warming at twice the global average rate, ocean currents around Japan have begun to show totally different aspects, affecting not only weather but also fisheries. In recent years, the catch of Pacific saury and Japanese flying squid has been dropping drastically, while Japanese amberjack has expanded its habitat greatly northward.

The area around Japan is characterized by the world’s largest ocean heat release to the atmosphere in winter and recognized as a “Climatic Hotspot” representative of the western boundary regions of the world oceans.  At the same time, the area is unique due to the existence of the Japan Sea between Japan and the continent.  Through the previous Hotspot1 (JFY2010-14) and Hotspot2 (JFY2019-23) projects supported by MEXT Grant-in-Aid for Scientific Research on Innovative Areas, we have investigated mid-latitude air-sea interaction and its change under global warming.  In the new Habitable Japan project (Hotspot3. JFY2024-28), we will expand our domain to atmosphere/ocean chemistry, marine ecosystems, and fisheries, aiming to answer the question “Will mild climate and abundant water/fisheries resources persist as a basis of survival for those of us living in Japan in the future?”

Research Group A01: Understanding of mid-latitude atmosphere/ocean variability under global warming

We will clarify variations/changes of ocean currents around Japan and their impact on coastal MHWs and marine ecosystems (A01-1).  We conduct shipboard observations in the Japan Sea (Jan. 2026) and in the North Pacific off the Sanriku coast and in the East China Sea southwest of Kyushu (both Jun.-Jul. 2026) to clarify the influence of oceanic fronts and MHWs on atmospheric circulation and rainfall (A01-1/A01-2).  We will also be clarifying the mechanism sustaining large-scale atmosphere/ocean heat and cold waves around the East Asia and the North Pacific (A01-3).

Research Group A02: Development of new methods and identification of basic processes

We will deploy profiling floats around the Kuroshio Extension to clarify biological production/decomposition (A02-4). We will also be conducting continuous observations at an island in the Japan Sea and another in the North Pacific to clarify the influence of aerosol particles generated from wave spray on heat/material exchanges across the sea surface (A02-5). We will additionally be creating a new data assimilation method that overcomes many discontinuities in the atmosphere/ocean fields to reproduce atmosphere-ocean-marine ecosystems coupling processes in the models (A02-6).

Research Group A03: Prediction and sustainability evaluation of mid-latitude atmosphere/ocean variability

We will evaluate the predictability of extreme oceanic events such as the Kuroshio large meander and MHWs, and clarify their impact on fisheries resources (A03-7).  We will also take on prediction of monsoon modulating under global warming and that of extreme weather such as heavy rainfall/snowfall inherent in monsoon (A03-8).  We will also further clarify variability and future change of mid-latitude climate that interact with the tropics and polar regions from a global perspective (A03-9).

Observation and numerical simulation are the two wheels of our Habitable Japan project. The observations include intense shipboard surveys in the Japan Sea and Pacific off Tohoku and in the East China Sea southwest of Kyushu, deployment of autonomous profiling floats with biogeochemical sensors around the Kuroshio Extension, and monitoring of aerosol particles on islands in the Japan Sea and Pacific. We will also diagnose and predict atmosphere/ocean phenomena by multiply using numerical models with different spatiotemporal scales and parameters, from regional models to global ones. Through these efforts, we will create integrated atmosphere and ocean science across atmosphere, ocean, and fisheries, and build a foundation for future predictions and projections.