Why are dewdrops not formed on a cloudy night?

Question

Accepted Answer

Clouds reflect back the Earth's radiation. Quick Verdict: Dew formation requires the Earth's surface to cool down significantly. On a cloudy night, clouds act like an insulating blanket, reflecting/re-radiating outgoing terrestrial radiation back to the surface. This keeps the ground too warm for condensation to occur. Thematic Discussion: The Physics of Dew Formation To understand why clouds prevent dew, we must first understand the strict conditions required for dew to form: Clear Skies: Allows outgoing longwave (terrestrial) radiation to escape freely into space, rapidly cooling the Earth's surface. Calm Air: Winds mix the air layers and carry moist air away; the still air allows moisture to settle. High Relative Humidity: Plenty of moisture must be available in the air. Cold and Long Nights: Gives the surface enough time to cool down below the dew point. The Cloudy Night Effect (Why Option B is correct): During the day, the Earth absorbs shortwave solar radiation. At night, it releases this heat back towards space as longwave terrestrial radiation. When the sky is clear, this heat escapes, and the ground gets very cold. However, when the sky is cloudy, the water vapor and water droplets in the clouds block this outgoing heat and radiate/reflect it back to the Earth's surface. Consequently, cloudy nights are significantly warmer than clear nights, preventing the ground from cooling enough to form dew. What is the "Dew Point"? The capacity of an air mass to hold water vapor is directly tied to its temperature (warm air holds more water). The dew point is the exact temperature at which the air becomes 100% saturated with water vapor. If the air cools beyond this point, it can no longer hold the water as a gas, and condensation occurs on solid surfaces (like grass or car windshields). If the dew point is above 0°C, condensation takes liquid forms (dew, fog, rain). If the dew point is below 0°C, condensation takes solid forms (frost, snow, hail). Source Note: For foundational clarity on dew formation, refer to Chapters 11 (Water in the Atmosphere) in the Class 11 NCERT book, "Fundamentals of Physical Geography."   📝 Mains Practice Question (GS Paper 1 - Physical Geography): Explain the concept of the Earth's Heat Budget. How do atmospheric elements like clouds and water vapor influence terrestrial radiation and the radiational cooling of the Earth's surface? (150 words, 10 marks)