The Dipole Mode of Summer Wet-Bulb Temperature Over Eastern China and the Possible Mechanisms

One prominent mode of the variability in the summer wet-bulb temperature (WBT) over eastern China exhibits a distinct north-south dipole pattern. This pattern demonstrates a positive center in northern China (NC), while a negative center is observed in southern China (SC). Our results indicate that the dipole mode of WBT could be partially ascribed to the impact of spring snow anomalies in eastern Europe-western Siberia (EEWS). The reduction in the snow depth, coupled with dry soil conditions, enhances the surface heat flux and consequently leads to an increase in the near-surface air temperature. The signal of soil moisture could persist from spring to summer, stimulating the generation of zonal Rossby waves. Consequently, the significant wave flux anomalies propagate from EEWS downstream and influence the atmospheric circulation over eastern China. These patterns play a role in the increase in the surface air temperature and moisture accumulation over NC, ultimately leading to the establishment of the dipole mode of WBT over eastern China in summer. Further analysis indicates that the atypical low sea surface temperature in the tropical Ocean, induced by the El Nino-Southern Oscillation, establishes a climatic context favorable for the persistence of an anomalous cyclone in the Northwest Pacific (NWP) throughout the summer season. The strengthened convection over the NWP and SC induces a dipole pattern of atmospheric circulation by stimulating a meridional wave train. This pattern creates favorable temperature and moisture conditions, contributing to the development of the dipole mode of the summer WBT across eastern China. In recent decades, the social loss associated with high-temperature and high-humidity conditions has sharply increased. The wet-bulb temperature (WBT) is widely regarded as a highly effective metric for characterizing the combined stress of humidity and heat. In this study, we emphasized one of the important modes (a north-south dipole pattern) of the variability in the summer WBT over eastern China and revealed the corresponding underlying mechanisms. We found that mid-high and low latitudinal dynamic processes may exert a synergistic effect on WBT over eastern China. On one side, spring snow depth anomalies could be coupled with spring soil moisture anomalies over eastern Europe-western Siberia and subsequently influence the dipole mode of the summer WBT over eastern China by triggering the stimulation of zonal Rossby waves. On the flip side, the anomalous low sea surface temperature in the tropical Ocean, driven by the ENSO, could yield a climatic state that supports the prolonged existence of an anomalous cyclone over the Northwest Pacific throughout the summer season. This cyclone exerts a significant impact on the dipole mode of the summer WBT over eastern China. Our study compensates for the lack of humid heat effect-related research across eastern China and contributes to establishing a solid theoretical foundation for comprehending and forecasting the summer WBT in the region. One significant pattern of the variability in the summer wet-bulb temperature (WBT) over eastern China is manifested as a north-south dipole mode Anomalous spring snowfall over Eurasia can impact the dipole mode of summer WBT over eastern China via the stimulation of zonal Rossby waves The anomalous sea surface temperature over tropical ocean, triggered by El Nino-Southern Oscillation, establishes a climatic context conducive to the dipole mode over eastern China