Enhanced Intensity of Interannual Variability of Summer Extreme Heat Events in the Mongolian Plateau during the Period 1979–2018 and Its Connection with the East Asian Polar Front Jet

Abstract This study investigates the changes in the interannual variability of the summer extreme heat events in the Mongolian Plateau (MP-EHEs) in 1979–2018. It is revealed that, during 1997–2018 (P2), the interannual variability of MP-EHEs increased by 114% compared to that in 1979–96 (P1). The results suggest that this intensification was associated with an interdecadal shift in the variability of the contemporaneous summer East Asian polar front jet (EAPJ). During P2, summer EAPJ was strengthened, exhibited stronger interannual variability, and had a tighter connection with a weakened summer East Asian subtropical jet (EASJ). Therefore, an anomalous high pressure was formed over the MP. The anomalous high pressure enhanced descending motions over the MP and a significant reduction in middle to low cloud cover, allowing more solar radiation to reach the surface. The increased solar heating contributed to surface warming, which further amplified the interannual variability of MP-EHEs. In contrast, during P1, summer EAPJ did not strengthened significantly, displayed weaker interannual variability, and maintained a less pronounced connection with summer EASJ. As a result, the anomalous high pressure over the MP was not strengthened significantly, resulting in a weaker modulation of the conditions that drive MP-EHEs and the insignificant linkage between summer EAPJ and MP-EHEs. The absence of the summer EAPJ-related anomalous high pressure and the associated radiative effects during P1 contributed to a lower intensity of interannual variability in MP-EHEs. Therefore, the enhanced summer EAPJ variability emerged in P2 was a critical factor driving the intensified MP-EHEs variability. Significance Statement Extreme heat events (EHEs) have become more frequent and intense due to climate change, posing serious risks to human health, agriculture, and ecosystems. The Mongolian Plateau (MP), with its distinctive climate and geography, is particularly vulnerable to these events. Therefore, gaining a deeper understanding of summer EHEs variability in the MP is critically important. In this study, the variability of enhanced summer EHEs in the MP (MP-EHEs) during 1997–2018 and its possible mechanisms are investigated. The findings indicate that such an enhancement was closely associated with the increased East Asian polar front jet (EAPJ) variability. In 1997–2018, the amplified EAPJ variability has exerted pronounced effect on strengthening the anticyclonic circulation over the MP, contributing to the formation of the summer MP-EHEs. These results provide valuable insights into the dynamics of summer MP-EHEs variability over the MP.