Why is the temperature difference between day and night large in Spring and Autumn and small in Xia Dong?

The key here is the water vapor content and sunshine in the air.

Insufficient sunshine in winter and insufficient evaporation of water vapor on the ground or water surface make the air dry. The heat from the sun shining on the ground is easily lost. So the temperature difference is small. In summer, on the other hand, there is plenty of sunshine, large evaporation of water vapor and high air humidity, so the heat on the ground is not easy to be lost at night. So the temperature difference is small.

The sunshine increases in spring, but the water vapor increases slowly, the temperature rises quickly during the day, and the heat is lost quickly at night. So the temperature difference is large.

In autumn, the sunshine begins to decrease, the evaporation of water vapor decreases, and the air is dry, so the air is crisp in autumn. The sun heats up quickly during the day and loses heat quickly at night. So the temperature difference is large.