Intraseasonal Oscillation of Summer Extreme High Temperature in Northeast China and Associated Atmospheric Circulation Anomalies

Abstract

Previous studies have demonstrated the important effects of intraseasonal oscillations in the tropics on the occurrence of extreme-high-temperature events (EHTs), whereas the influence of intraseasonal oscillations in mid-high latitudes on EHTs has been less discussed. In this study, the intraseasonal oscillation of summer extreme high temperatures from 1981 to 2019 in northeast China and its associated atmospheric circulation were studied using conventional statistic methods. The results show that the summer extreme-high-temperature distribution in northeast China is consistent throughout the whole region, with a low-frequency oscillation period of 10–30 d. The low-frequency extreme-high-temperature events (LFEHTs) in northeast China account for 88.8% of all EHTs during the summer. The corresponding low-frequency circulation anomalies with 10–30 d oscillations exhibit a barotropic wave-train moving from west to east in the mid-high latitudes of Eurasia. A low-frequency wave-train index (LFWI) was defined to characterize the wave-train anomaly system in the mid-high latitudes of the Eurasian continent. The LFWI may be a potential precursor for forecasting LFEHTs about 7 days in advance. It could explain 15–30% of the summertime low-frequency daily maximum temperature variability in northeast China.