Article ID: 2020-009
In 2018, heatwaves (HWs), which are defined as period of abnormally hot weather with the daily maximum temperature (T_Max) exceeding its 95th percentile threshold for at least three consecutive days, were prevalent during June to August, and temperature records were broken in many countries over East Asia (EA) including China (CH), Japan (JP), and the Korean Peninsula (KP). In particular, extreme HWs through July to August lasted for the longest duration with 21.3 days with T_Max reaching 36.9°C. The highest T_Max, recorded since 1907, exceeded to 41°C in Hongcheon, located east of Seoul in the KP. Here, we examine the factors that influenced the 2018 HW, and how these relate to the 1994 HW, which was second longest HW recorded in the KP. The results show that abnormally strong and northwestward extended anticyclone features observed in July 2018 lasted as a persistent North Pacific anticyclone anomaly until August 2018 centered at the northern KP. These anticyclone features subsequently formed as a modon-like blocking with a cyclonic anomaly in the East China Sea. Meanwhile, in August 1994, the North Pacific High (NPH) extended to eastern EA, which broked the meridional dipole structure and HWs do not persist. The NPH, which persisted till August 2018, was accompanied by a sinking motion, suppression of precipitation, anomalous maximum temperature, weakening of the westerly jet stream, and increased insolation due to clear sky. We find that the prolonged and northwestward-shifted NPH including the KP drove the extraordinarily hot 2018 summer in Korea. In addition, low precipitation and massive evapotranspiration with the persistent insolation in July 2018 influenced the dry condition at the surface. We suggest that the predictions for the location and duration of the NPH associated with the HWs are required to reduce heat-related mortality and the impact on agriculture due to excessive evapotranspiration.