Abstract
The South Asian high (SAH) index was defined using the 200 hPa geopotential height for 1973ā2019. Of the movements of the SAH center in the northāsouth, eastāwest, northwest-southeast, and southwest-northeast directions, the movements in the northwest-southeast direction showed the highest positive correlation with heatwave days (HWDs) in South Korea. Thirteen years with the highest values in the northwestward shift of the SAH (positive SAH years) and 13 years with the highest values in the southeastward shift of the SAH (negative SAH years) were selected from a time series of SAH indices from which the linear trend was removed, and the differences between these two groups were analyzed. An analysis of vertical meridional circulation averaged along 120Ā°ā130Ā° E showed that in the latitude zones containing Korea, anomalous downward flows with anomalous high pressures formed in the entire troposphere and coincided with a positive anomaly of air temperature and specific humidity. An analysis of stream flows and geopotential heights showed that in the positive SAH years, anomalous anticyclones developed in Korea, the North Pacific, North America, Western Europe, and the Iranian Plateau. These anticyclones had the wavenumber-5 pattern and showed more distinct barotropic vertical structures at higher altitudes, which resembled the circumglobal teleconnection (CGT) pattern. The maintenance of CGT depends on the interaction between the CGT circulation and the Indian summer monsoon (ISM), which has a major influence on the mid-latitude atmosphere. Strengthening of the ISM results in the formation of upper-level anomalous anticyclones in the northwestern Iranian Plateau and produces continuous downstream cells along the waveguide due to the Rossby wave dispersion. When diabatic heating by Indian summer monsoon precipitation is strengthened, the SAH is strengthened to the northwest of India, and a positive CGT pattern is formed. As a result, anomalous anticyclones formed in all layers of the Korean troposphere, resulting in heatwaves, tropical nights, and droughts exacerbated in South Korea.
Highlights
A heatwave is a period of sweltering weather, but it lacks a clear definition
During positive South Asian high (SAH) years, the heatwave days (HWDs) can increase more in Korea, whereas during the negative SAH years, the SAH develops more to the southeast, and the western North Pacific subtropical high (WNPSH) extended to the southwest (Fig. 8b), which results in an overlap of the two high-pressure systems in southern China
This occurs because the WNPSH develops in the northwestern direction to the Shandong Peninsula during the positive SAH years, whereas during negative SAH years, tropical cyclones (TCs) mainly move from the far eastern sea of the Philippines to the East China Sea (ECS) and to Korea and Japan, or to the west toward the Indochina Peninsula
Summary
A heatwave is a period of sweltering weather, but it lacks a clear definition. A heatwave is one of the most dangerous. Convective activities in the tropical and subtropical monsoon regions can influence heatwaves and heavy rainfall events in mid-latitude through various teleconnections in an El NiƱo/La NiƱa phase-dependent manner (Ding et al 2011; Lee et al 2011, 2017b; Lee and Ha 2015; Ha et al 2018; Lee 2018; Yeo et al 2019). When convection is active in the Indian monsoon region, a circumglobal teleconnection (CGT) covering the entire northern hemisphere develops, increasing the risk of heatwaves in the East Asian region (Ding et al 2011). When this occurs, Rossby wave dispersion is dominant in the zonal direction; Yeo et al (2019) called this a āZ-wave teleconnectionā.
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