Why does China become the coldest country at the same latitude in the world in winter?

In winter, after the cold wave and strong winds stop, the weather gradually warms up under the warm sun. However, the good times do not last long. A second cold wave often moves south one after another, and the temperature drops sharply again. If you plot the daily average temperatures into a curve, the shape of the curve would be like the waves of the sea or steep peaks. It can be seen that the winter in our country is particularly cold mainly because of the cold air that often blows from the north in winter. If there is no cold wave going south and the temperature reaches the latitudinal average level, Harbin will be as warm as Xuzhou and Zhengzhou, Beijing will be warmer than Nanchang and Changsha, and Shanghai will be as warm as Nanning and Guangzhou without winter!

Where do these cold waves come from? They come from Siberia in the Soviet Union. Some cold waves also come from the Arctic Ocean, but they also have to pass through Siberia. Siberia is the coldest place in the northern hemisphere in winter. In Verkhoyansk and Oymyakon on the Arctic Circle, the average temperature in January is nearly -50°C, and the absolute minimum temperature is as low as -72°C. Such severe cold air comes to our country (although the high sun is shining all the way The temperature has increased due to the baking of the warm ground), which of course makes the eastern part of my country the low-temperature "champion" at the same latitude. However, most areas in southwest Sichuan Province and Yunnan Province in my country are in the dry and warm southwesterly airflow from Southwest Asia in winter, and the climate is very warm: Kunming City, with an altitude of 1891 meters, has an average temperature of 7.8°C in January, which is at the same latitude as the east. The altitude is only 1,167 meters above sea level, but Guilin is controlled by a cold wave and cold air flow (the average temperature in January is 8.0°C). Another example is Yuanmou, which is 1,118 meters above sea level in the dry and warm valley of the Jinsha River in Yunnan Province. The temperature in January is as high as 15.5°C. But it is 9.7°C higher than Lin County, Hunan, which is only 185 meters above sea level at the same latitude... However, we must know that in winter, the temperature in southern my country decreases by an average of 4 to 5°C for every 1 kilometer increase.