Changes in compound hot extremes over the mid-high latitudes of Asia and underlying mechanisms

Abstract This study investigates the spatiotemporal variations of summer frequency of day-nighttime compound extreme high-temperature events (FCEHE) in the mid-high latitudes of Asia (MHA) from 1979 to 2014. Results show that FCEHE has shown an upward trend with fluctuations, especially in Mongolia-Baikal. The descending anomaly caused by the anomalous high pressure over the Mongolia-Baikal results in reduced cloud cover, which increases solar radiation reaching the ground, favoring the higher FCEHE. This process is consistent during the daytime and nighttime periods, with relatively limited nighttime solar radiation, potentially compensated by the increased downward longwave radiation to sustain the extreme high temperatures. This benefit process is closely connected with two main factors: the increased sea ice in the Barents Sea during spring and the anomalously warm sea surface temperature (SST) in the Northwest Pacific during summer. The increased sea ice can affect the Eurasia teleconnection (EU), while the warm SST affects the Pacific-Japan/East Asia–Pacific pattern (PJ/EAP). Subsequently, these factors further modulate the circulation anomalies and then FCEHE.