Where does the air in the north come from in winter?

The distant Arctic Ocean and cold Siberia are the cradles of cold air.

The cold air originally came from the Arctic Ocean, and later strengthened through Siberia. These areas have high latitude, long winter nights, short days and few sunshine hours. In the polar regions, there will even be extreme nights, and the sun never shows its face. Therefore, the earth's heat from the sun is very weak; However, at night, the ground radiates a lot of heat into space. With the continuous cooling of the ground, the temperature of the atmosphere near the ground is getting lower and lower, and the accumulation of cold air will increase. Guided by the northwest airflow, this cold air reactor with extremely low temperature will push from north to south, affecting Mongolia, North China, East China or most of China.