Changing human-sensible temperature in Korea under a warmer monsoon climate over the last 100 years

This study explores changes in means and extreme events of human-sensible temperature (HST), which is quantified by selective combination of Universal Apparent Temperature, Heat Index, and a new Wind Chill Index, in Korea for the last 100 years (1919-2018) and illustrates the synoptic patterns of the East Asian monsoon system (EAMS) for extreme HST events. The time series analyses show that HST has increased much faster than near-surface air temperature (AT) in winter due to decrease in wind chill as well as to increase in AT. On the other hand, HST in summer, which is higher than AT on average because of high humidity in monsoon climate, has increased at a slow rate compared with those in other seasons. However, more extremely hot, long-lasting HST events have been observed in recent decades, as in 1994, 2013, 2016, and 2018, with shorter recurrent intervals. Greater increases of HST than AT are more distinct in the southern region under maritime subtropical climate than in the temperate climate zone in the north in all seasons. Composite maps for multiple high or low HST extreme events reveal that a dipole pressure anomaly pattern, rather than the intensity at the center of these air masses, is more closely related to the frequency of extreme HST events in Korea: A west high-east low pattern in winter formed by the expansion of the Siberian High accompanying an intense migratory low pressure system, and a south high-north low pattern formed by the westward intrusion of the Northwest Pacific subtropical high in summer after earlier terminations of summer rainy period (Changma). These indicate that monitoring of changing EAMS's characteristics is crucial to the mitigation of potential damages caused by unprecedented HST extreme events in the warmer twenty-first century.