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.
Highlights
With the continuous rise in global temperature, extreme-high-temperature events in northeast China are increasing [1], posing more threats to society, including economic losses and an increase in health risks in this significant warming region [2–7]
The first mode of empirical orthogonal function (EOF) (EOF1) accounted for 69.2% of the total variance and showed that the extreme-high temperatures during the summer in northeast China exhibited a consistent variation in the whole region (Figure 1a), which is similar to the results of previous studies [54,55]
It can be seen from the time coefficient of the first mode (PC1) that the extreme-high-temperature in northeast China was characterized by obvious intraseasonal changes with a short cycle (Figure 1b), which was confirmed in the power spectrum analysis of PC1 with a significant 10–30 d period (Figure 1c)
Summary
With the continuous rise in global temperature, extreme-high-temperature events in northeast China are increasing [1], posing more threats to society, including economic losses and an increase in health risks in this significant warming region [2–7]. Those threats can be reduced by improving early forecasting of summer temperatures in northeast China, especially the extended weather forecasting, whose signal can be from the atmospheric intraseasonal oscillation (ISO) [8]. ISO usually refers to an oscillation phenomenon with a 10–90 d period that occurs in the atmosphere [9]. Investigating the relationship between extreme-high temperatures in northeast China and associated ISO is vital
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