Climate Indices and Atmospheric Circulation Patterns Linked to East Asian Summer Wet‐Bulb Temperatures

ABSTRACT

This study investigates the variability of East Asian summer wet‐bulb temperature (Tw) using ERA5 reanalysis data for 1979–2023. Statistical analysis of Tw anomalies was conducted to identify the dominant patterns of regional variability and their associations with large‐scale atmospheric circulation and climate indices. Tw exhibited a significant upward trend across most of East Asia, with particularly pronounced increases over northern China, the Korean Peninsula and northern Japan, indicating intensifying humid heat under global warming. After removing the linear trend, two dominant modes of regional Tw variability were identified, characterized by contrasting meridional and zonal dipole patterns. The meridional dipole was associated with an anticyclonic circulation anomaly over East Asia, enhanced convection near the Philippine Sea and anomalous moisture transport from the western North Pacific. In contrast, the zonal dipole was linked to a Siberia–Okhotsk wave‐train pattern and La Niña‐like conditions in the tropical Pacific, accompanied by anomalous moisture transport near northern Japan. Thermodynamic decomposition further revealed that humidity variations contributed more substantially to the first two dominant modes, whereas temperature variations played a larger role in the third mode. These findings demonstrate that regional contrasts in East Asian summer Tw variability are associated with multiple large‐scale circulation configurations and distinct thermodynamic contributions, highlighting the importance of considering both atmospheric moisture and temperature variability in understanding regional humid‐heat changes.