Possible relationship between heatwaves in Korea and the summer blocking frequency in the Sea of Okhotsk

Abstract

This study examined the relationship between heatwaves in Korea and blocking in the Sea of Okhotsk (OK) region, which significantly influences the Korean climate in summer. According to the analysis, negative correlations were observed between the blocking frequency in the OK region and heatwave days (HWD) and the surface air temperature (SAT) in Korea over the past four decades (1979–2018). These negative correlations suggest that when the blocking frequency in the OK region increases in summer, the HWD and SAT decrease in Korea. This study selected 10 years of high blocking frequency years (high BF years) and 10 years of low blocking frequency years (low BF years) and analysed the differences between the two groups to explain the negative relationship between the HWD in Korea and the blocking frequency in the OK region. The difference between the two groups revealed strong anomalous anticyclonic and cyclonic circulations that developed in the north Siberia region and northeast Australia (NEA), respectively, throughout all layers in the troposphere. The large anomalous anticyclonic pattern in the North Siberia region was related to the blocking high, while the anomalous cyclonic pattern that developed in NEA was related to the East Asian summer monsoon (EASM) front. The difference in the sea surface temperature (SST) between the two groups was also analysed. In the North Atlantic Ocean, a tripole structure appeared with a cold anomaly in the high latitudes, a warm anomaly in the mid‐latitudes and a cold anomaly again in the low latitudes, which is a typical spatial distribution of the SST anomaly related to the positive North Atlantic Oscillation (NAO) phase.

Characteristics of precipitation in East Asia associated with Okhotsk Sea blocking in June and July

“…Based on the onset date of the OKB events, 21, 16, and two events are observed in June, July and August, respectively, indicating that the events tend to decrease over time during the summer. These results are consistent with those of Choi et al (2022). The OKB events in August are excluded from composite analysis because their number is insufficient.…”

“…Most studies of the relationship between climate and blocking over the Northern Hemisphere focus on winter or spring when blocking is most frequent (e.g., Cheung et al, 2013; Kim & Ahn, 2022; Wiedenmann et al, 2002). However, the extreme weather events associated with blocking, such as heat waves and heavy rain, have recently been reported in the Northern Hemisphere during summertime (e.g., Chen et al, 2021; Choi et al, 2022; Li et al, 2020;Park & Ahn, 2014; Song & Ahn, 2022). The blocking phenomenon is directly related to the dipole precipitation anomaly pattern, which is characterized by drier conditions in the blocked regions and wetter conditions south of the blocked regions (e.g., Fernandes & Rodrigues, 2018; Rodrigues & Woollings, 2017; Sousa et al, 2016, 2017).…”