Impact of Pacific-Japan pattern on temperature and heatwave events in summer over Taiwan

The prediction of heatwave events is vital to provide information on possible hazards caused by extremely high temperature. The Pacific-Japan (PJ) pattern is a significant climate variability that controls the summer climate over East Asia. Previous studies have reported that the meridional propagating wave structure associated with the PJ pattern can modulate summer temperature and heatwave characteristics over northeast Asian countries, such as Korea and Japan. Nevertheless, its impacts on the subtropical regions, including Taiwan, a mountainous subtropical island with an approximate population of 24 million, is not yet fully understood. In this study, we investigate the impacts of the PJ pattern on the summer temperature and heatwave characteristics in Taiwan on the interannual timescale using long-term station-based temperature and rainfall dataset. We found an island-wide increase in temperature during the positive phase of the PJ pattern, which is characterized by an anticyclonic anomalous circulation over Taiwan. Meanwhile, the averaged effective area and frequency of heatwave extremes over Taiwan have increased significantly, indicating an increase of exposure to heatwaves. Our examinations of large-scale environment suggest that the adiabatic warming due to subsidence anomaly associated with the anticyclone over Taiwan is primary contributor of surface warming, which is balanced by diabatic cooling and meridional advective cooling on a seasonal timescale. Our study consolidated the links between the PJ pattern as a climate driver, hot summers and increased summer heatwave events over Taiwan. By combining with the seasonal prediction systems and early warning systems, such understanding can help sectors that are vulnerable to heat stress to prepare for potential hazards.

Automated summary

In this study, the impacts of the Pacific-Japan (PJ) pattern on the summer temperature and heatwave characteristics in Taiwan were investigated using long-term station-based temperature and rainfall dataset. The results showed that during the positive phase of the PJ pattern, there was an island-wide increase in temperature in Taiwan, accompanied by an increase in the effective area and frequency of heatwave extremes. The adiabatic warming due to subsidence anomaly associated with the anticyclone over Taiwan was identified as the primary contributor to the surface warming.