Why is it colder on clear nights?

clear skies at night

This is something that fans of astronomy will know well and will have noticed. In fact, it is applicable to any time of the year. A clear night is usually accompanied by a drop in temperatures. Contrary to what can happen from the first hour of the day, if we have cloud cover we will have a colder environment than when there is no cloud cover, we will have more heat.

As last night, the sun's rays diminish, until no more arrives, and the infrared radiation from it ceases. If we have a cloudy sky, radiation is trappedIt is difficult for him to go out and with it the heat. On the contrary, absence of clouds, causes a dissipation of this heat and radiation, and having no barrier that can store it, it leaves leaving a cold night and in turn a sky so clear and starry.

The phenomenon during the day and in the desert

starry night cloudless desert

Similarly, during the day, cloud formation prevents radiation from penetrating at ground level. When they "collide" with the clouds, they fail to pass all of them. This is also called refraction, since the direction of the ray changes by passing through a different medium than the one it comes from. It would be called a reflex, if when it collided it bounced and changed direction. By not penetrating them, this lack of radiation reduces the temperature during the day. If at night that cloudiness is lost, the drop in temperatures is more pronounced.

An example, contrary we could see it in summer. A very sunny day, with terrible heat, with a night accompanied by clouds, causes that the heat that has been stored can hardly dissipate. Then we have one of those torrid nights where sleeping becomes quite an odyssey. That is the double effect of clouds on thermometers depending on the time we are. Clouds by day is cold, at night it is heat, absence of them in the day is heat, and cold at night.

That is also why the high temperatures in the desert during the day, and those freezing nights. As there are almost never clouds, it produces those very high contrasts.


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