Second Changma retreat variability in Korea using the available water resources index and relevant large‐scale atmospheric circulation

ABSTRACT This study investigated the variability in the second Changma retreat date (SCRD) in Korea and the characteristics of the relevant large‐scale atmospheric circulation using the available water resources index (AWRI). The analysis of the SCRD and meridional winds at the 850 hPa level over 30 years (1982–2011) showed that the climatological mean SCRD in Korea is 3 September, and the late (early) retreat is associated with the development of a cyclonic (anticyclonic) circulation anomaly in the western Siberian region and an anticyclonic (cyclonic) circulation anomaly in the western Pacific region and the Aleutian Islands region. This study defined a new second Changma retreat index (SCRI) using the three regions with the highest correlation between the SCRD and 850 hPa meridional winds and analysed the variability and characteristics of the SCRI between the low‐ and high‐SCRI years. In Korea, the largest differences in SCRD between the low‐ and high‐SCRI years appeared in the vicinity of Jiri Mountain and the western region of Gangwon‐do province. The difference in the AWRI between the low‐ and high‐SCRI years increased significantly from August to December and peaked at the end of September. The analysis of precipitation data revealed that the SCRD of the Korean regions with high rainfall that exceeded 5 mm day−1 during the low‐SCRI years was about 3 weeks earlier than during the high‐SCRI years because of the early development of a cold and dry continental high system. During the low‐SCRI years, a cold and dry anticyclone anomaly developed from the western Siberian region to the East Asian mid‐latitude region while the western North Pacific subtropical high weakened further in the western Pacific, and the Aleutian Low developed in the vicinity of the Aleutian Islands during the low years. These characteristics of a large‐scale atmospheric circulation explained most interannual SCRD variations.