Why is the climate in Northeast China very different in one day?

The most important factor affecting temperature is direct sunlight.

The most important factor affecting direct sunlight is the thickness of clouds.

The sun emits short-wave radiation to the earth, and the temperature rises after being absorbed by the surface, while the surface also emits long-wave radiation to space at night, which is easily absorbed by greenhouse gases and clouds (the origin of the greenhouse effect). After absorbing this long-wave radiation, the temperature will rise.

Autumn is crisp in most parts of our country. In short, there are no clouds during the day and night.

There are no clouds during the day, the sun reaches the ground unimpeded, and the temperature is easy to rise.

There are no clouds at night, no clouds absorb long-wave radiation, and the greenhouse effect is not strong. So the temperature drops quickly.