Two types of cold surges of Korea and their predictability in Korea Integrated Model (KIM)

Extreme cold events in East Asia have significant socio-economic impacts, and accurate prediction is crucial for effective risk management. Understanding cold surges requires consideration not only of their intensity but also their duration. Some cold surge events are notable for their prolonged duration. Meanwhile, cold surges accompanied by abrupt temperature fluctuations have become increasingly frequent in recent years. These drastic cold surges pose substantial risks to human lives and energy supply. In this study, cold surge events in Korea are classified into two types based on their temporal characteristics. Prolonged type cold surges last about three weeks, while drastic type cold surges are defined by a difference of 8˚C or more between the lowest and highest temperatures within a three-week span. It is observed that a trough over East Asia stagnates due to a blocking high over the northeastern Pacific under negative Arctic Oscillation conditions, leading to prolonged cold surges. Conversely, drastic cold surges occur in association with the Madden Julian Oscillation (MJO). Specifically, when the MJO phase spans through 8-1-2-3, warm conditions over East Asia are followed by cold surges. The predictability of these features in the Korea Integrated Model (KIM) has been investigated. KIM demonstrates skillful prediction capability by capturing both types of cold surges within a 2-week lead time. However, as the forecast lead time increases, the predictability of drastic type cold surges tends to surpass that of prolonged type. This is attributed to the better predictability of tropical convection compared to blocking over the northeastern Pacific. This study will provide detailed descriptions of the dynamical characteristics of the two types of cold surges and their subseasonal predictability sources.