Why are dewdrops not formed on a cloudy night?

[amp_mcq option1=”Clouds absorb the radiation released from the Earth’s surface.” option2=”Clouds reflect back the Earth’s radiation.” option3=”The Earth’s surface would have low temperature on cloudy nights.” option4=”Clouds deflect the blowing wind to ground level.” correct=”option1″]

This question was previously asked in

UPSC IAS – 2019

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The correct answer is A) Clouds absorb the radiation released from the Earth’s surface.

Dew forms when the temperature of a surface drops below the dew point of the surrounding air, causing water vapor to condense. On a clear night, the Earth’s surface radiates thermal energy (long-wave radiation) into space. This outgoing radiation leads to significant cooling of the ground surface.
On a cloudy night, clouds act as a thermal blanket. They efficiently absorb the outgoing long-wave radiation emitted by the Earth’s surface. The absorbed energy warms the clouds, and they re-emit radiation in all directions, including back down towards the Earth’s surface. This downward radiation reduces the net loss of heat from the surface.

Because the clouds reduce the net radiative cooling, the Earth’s surface and the air near it do not cool down as much on a cloudy night compared to a clear night. If the temperature does not drop sufficiently to reach the dew point, dew will not form. Option A accurately describes the key process (absorption of radiation) that prevents significant surface cooling. While clouds also re-emit radiation back (related to Option B), the initial absorption is the mechanism by which they trap the outgoing heat. Option C is incorrect because cloudy nights are typically warmer than clear nights due to the blanketing effect. Option D is irrelevant to dew formation by radiation.

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