Why is the temperature difference between north and south in China large?

in winter, the lowest temperature in the north sometimes drops to-4 ~-3℃, while the temperature in the south is mostly above ℃, and the lowest temperature is only a few degrees below zero. In summer, the temperature difference between the north and the south is very small. Why? This is because the temperature on the earth depends on the amount of solar radiation energy absorbed by the surface; The second is the strength of the surface thermal radiation ability. When the light intensity is high and the time is long, the ground will receive more heat from the sun, and at the same time, it will release more heat to the air, so the temperature will be high, on the contrary, the temperature will be low. China is located in the northern hemisphere, and the sun shines obliquely in the northern hemisphere in winter. However, due to the fact that the sunlight is more inclined to the north than to the south, the solar heat per unit area on the ground is less than that in the south, that is, the light intensity in the north is smaller than that in the south. In winter, the sunshine time in the south is longer than that in the north. For example, around the winter solstice, the sunshine time in Haikou, Hainan Island of China is about 1.9 hours, while that in Harbin, Heilongjiang Province is only about 8.6 hours. In summer, the situation is just the opposite. The illumination time in the north is longer than that in the south. For example, around the summer solstice, the daytime in Harbin is about 15.7 hours, while that in Haikou is only about 13.2 hours. In addition, in winter, the north is often affected by the prevailing northerly airflow, and the cold current frequently goes south, bringing cold weather that is far from possible in the local latitude; There is little northerly airflow prevailing in the south, and the temperature is still high. In summer, the southeast monsoon prevailing in the south continuously blows warm and humid air to the north. In short, in winter, the light intensity in the south of China is greater than that in the north, and the light duration is longer, and the prevailing northerly airflow has little influence, which causes a great difference in temperature between the north and the south; In summer, although the light intensity in the south is greater than that in the north, the light time is short, and the prevailing southeast monsoon blows to the north continuously, which reduces the temperature difference between the two. Therefore, the temperature difference between the north and the south in summer is small.