What does "crisp autumn" mean geographically?

Autumn is crisp, which means the sky is wide and the air is fresh and cool in autumn. It means that in autumn, the humidity is not as high as that in summer, and the clouds become thinner and thinner because of lack of water. Light clouds float in the high sky, the sky appears higher and wider, the temperature is no longer as hot as summer, and the air becomes fresh and cool.