Upper level cold core and low pressure system form some cut-off lows.
A temperature of -20 degrees Celsius at 500hPa can be found to have very strong cold air.
850 hPa
The 9 degrees Celsius line crosses the Korean Peninsula, so the temperature difference between 500hPa is 29 degrees .
Low-level warm moist air exists.
Surface
We can see the development of a strong low-pressure system over Korea. Rapid temperature gradient due to the folding phenomenon of the tropospheric surface can be seen, resulting in cold advection in Korea.