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)

In midlatitudes, persistent warm and cold air temperature anomalies are tied to a north-south shift of the jet stream. Such a shift often occurs as a regional manifestation of jet meandering from continental/ocean basin to hemispheric scales, and is linked to marine heat and cold waves (see the figure). In contrast to dry climates in inland regions, hot and cold extremes in islands and coastal areas are strongly constrained by the oceans which have larger heat capacity than the atmosphere. Understanding of atmosphere-ocean interactions and feedback processes is thus crucial for mechanism understanding of how the atmospheric circulation anomalies induce heat waves and cold spells in Japan. We investigate atmospheric and marine heat waves and cold spells as manifestations of atmosphere-ocean coupled variability and examine their spatiotemporal features, internal feedback mechanisms, seasonal predictability, and changes under climate warming.

1. This project studies features of heat waves and cold spells in the island and coastal regions of East Asia, contrasting with those occurring in inland dry areas. We describe how atmospheric circulation anomalies such as jet meandering evolve while interacting with the ocean and changing surface air temperature and sea surface temperature, and investigate the mechanisms.
2. We assess potential seasonal predictability by examining how atmosphere-induced oceanic anomalies persist and spread to affect the probability of atmospheric heat waves and cold spells.
3. The project further examines changes in atmospheric circulation variability and atmosphere-ocean interaction processes from the past to the future in the warming climate.

These studies are conducted by analyzing recent large ensemble atmosphere-ocean coupled climate model simulation data sets together with observational data.