Why is winter generally affected by cold front all over the country?

Affected by the difference of thermal properties between land and sea, in summer, high pressure is in the ocean, low pressure is in the land, in winter, high pressure appears in the land, and low pressure appears in the ocean. The weather in China is mainly influenced by the Asian low and Hawaiian high in summer, and by the Mongolian-Siberian high in winter. The subtropical high recedes to the sea surface and its power is weakened. China is located between the largest ocean and the largest continent, with obvious monsoon climate. Therefore, in winter, most parts of China are affected by the powerful Mongolian-Siberian high, and the northwest wind prevails, pushing the dry and cold air masses south.