This study examined the influence of atmospheric blocking on the variability of precipitation over South Korea during summer (June–July–August) by defining the blocking frequency over the Okhotsk Sea (Okhotsk Sea blocking frequency; OK_BF). According to composite analysis for the years of high precipitation over South Korea, blocking occurs more frequently over the Okhotsk Sea (140°E–160°E). Partial correlation and regression analyses were conducted to separate the contribution of OK_BF to precipitation variability from that of the low‐level meridional wind (LLMW) because LLMW over the region is another important aspect of summer precipitation in South Korea. The barotropic structures of positive geopotential height anomalies over the Okhotsk Sea associated with increasing OK_BF can induce negative temperature anomalies over South Korea due mainly to the equatorward advection of cold air masses from higher latitudes. The enhanced meridional temperature gradient can cause increases in baroclinic instability and zonal wind vertical shear according to the thermal wind balance. This instability can induce anomalous cyclonic circulations over South Korea, resulting in positive precipitation anomalies. The partial correlation coefficients (R2 = 0.35–0.40) between the OK_BF and precipitation indices, including mean precipitation, extreme precipitation intensity, wet days, and consecutive wet days, were all statistically significant at the 95% confidence level. Overall, the effects of the increasing OK_BF on both precipitation and potential evapotranspiration can intensify the surface water budget in South Korea.

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.

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