The purpose of this study is to explore spatio-temporal patterns of extreme low human-sensible temperature (HST) across Mt Halla (1,950m), Korea. To do this, decadal (2011/12-2020/21) averages of daily or hourly windchill index (WCI), which quantifies HST considering the combined effects of low temperature and strong wind, are calculated for 24 weather stations in Mt Halla. Time series of decadal average daily mean show that extreme low HST events with moderate risk level (-27~-10°C) occur in mid-winter (mid-January~early February) around the high mountainous areas of Mt Halla, while such risk does not exist in the low-elevated coastal regions of Jeju Island under subtropical climate. Strong wind around the subalpine climate belt lowers HST by 5°C than air temperature in mid-winter. In extreme cases when the advection of northerly cold wind is intensified by the west high-east low pressure pattern in East Asia, the HST around the peak of Mt Halla can be lowered to high risk level (-39~-28°C) in the early morning times of mid-winter days. These information about mountain bioclimate may help establish mountain extreme climate warning systems, which are needed to protect mountaineers from potential life-threatening accidents caused by extreme low HST events over high mountains such as Mt Halla.

The purpose of this study is to characterize the synoptic climatic patterns of extreme humansensible temperature (HST) events in Jeju Island, Korea under a subtropical climate condition as well as to examine their teleconnections with the large-scale climate systems. According to the extreme case analysis of the recent 30 years (1988-2017) data sets, the maximum daily average HST in the coastal areas of Jeju Island can rise up to about 40°C in mid-summer and even up to about 48°C during mid-daytime. These extreme HST events occur when the expansion of subtropical Pacific high pressure toward East Asia as well as the poleward shift of the Changma front provides hot and humid conditions over Jeju Island surrounded by seas, particularly in La Niña years with a positive (+) Arctic Oscillation mode. In contrast, the intensified western high and eastern low dipole pressure pattern in mid-winter, which accompanies the downward shear of upper tropospheric cold air toward the southern region of the Korean Peninsula under a negative (-) Arctic Oscillation mode, provides favorable conditions for frequent low HST extreme events. These conditions can lower daily average HST as much as -10°C in the coastal region of Jeju Island, and lower nighttime HST by -25°C on the peak areas of Mt. Halla due to wind chill effects. These findings will be used as a base for establishing prediction and warming systems of extreme HST events on Jeju Island, which is needed to mitigate the damage to the lives of Jeju residents and tourists under climate change.