This study investigates the north-south teleconnection spanning from the subtropics to high latitude that affects summer heat wave in Korea and the associated occurrence mechanism using observation data, NCEP/NCAR reanalysis I data, and outgoing longwave radiation (OLR) data for the period from 1973 to 2014. First of all, top 20 heat wave cases selected using heat wave total index (HWTI) are classified into 3 heat wave types (Typhoon, Okhotsk, and North Pacific high extension type), by considering synoptic scale characteristics and weather types. Heat wave circulation index (HWCI) is defined based on the geopotential height anomaly at 500hPa on the Peak day of heat wave years in order to measure the north-south teleconnection.
Results show that the HWCI accounts for typical synoptic pattern for Korean heat wave with the north-south wave-like structure which is characterized by a cyclonic circulation anomaly over the Philippine Sea, an anticyclonic circulation anomaly over the Korean peninsula and a cyclonic circulation anomaly over high latitude, indicating that the HWCI can be a remarkable index to represent the north-south teleconnection originating from the subtropical western Pacific. In addition correlation pattern between the HWCI and SST shows that the Korean heat wave in July to August is related to La Nina pattern with warm SST over the subtropical western Pacific lasting from February, indicating that the steady SST forcing can provide a favorable condition for active convective activity. Moreover the correlation patterns between the HWCI and other climate variables also shows a consistent north-south teleconnection pattern. Independent analysis using the OLR index defined by OLR value over the subtropical western Pacific also confirms that strong convective activity over the subtropical western Pacific induces a downward motion over the Korean peninsula through an intensification of local meridional circulation, and thereby provide a favorable large scale high pressure condition for shortwave heating and adiabatic warming over the Korean peninsula.
Thus this study emphasizes that the north-south teleconnection pattern originating the subtropics is one of the key components for the amplification of the Korean heat wave in July to August, especially Typhoon type heat wave, indicating that it needs the monitoring of convective activity over subtropical western pacific for the prediction of Korean heat wave.