Why are dewdrops not formed on a cloudy night?
Contents9
- AClouds absorb the radiation released from the Earth’s surface.
- BClouds reflect back the Earth’s radiation.
- CThe Earth’s surface would have low temperature on cloudy nights.
- DClouds deflect the blowing wind to ground level.
Show answer
Answer: (B) Clouds reflect back the Earth’s radiation.
The correct answer is (B) — Clouds reflect back the Earth's radiation.
Dew forms when the ground cools down enough at night for water vapour to condense on surfaces.
On a clear night, the Earth's heat radiates freely into space, cooling the ground quickly.
But on a cloudy night, clouds act like a blanket — they reflect the Earth's heat radiation back to the surface, keeping the ground warmer.
Since the ground doesn't cool enough, dew doesn't form.
Tip:
- Clouds = blanket at night.
- They trap heat → ground stays warm → no dew.
Dew formation requires the ground to cool enough at night for water vapor to condense, but clouds act like a blanket reflecting Earth's heat back down.
The question tests understanding of radiative cooling versus cloud insulation - a key concept in explaining why clear nights are colder than cloudy nights.
Dew Formation Mechanism
Geography dewdrops dew
Dew Formation: Conditions & Process
Dew forms when ground temperature drops below the dew point
Requires clear skies for maximum radiative cooling
Forms on grass, leaves, and metal surfaces that cool fastest
Dew formation is a nighttime cooling process where water vapor condenses into tiny droplets on surfaces. The key is rapid ground cooling through heat radiation to space.
Dew Formation Process
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Clear Night Sky**
No clouds to block radiation`"]
s2["`**Ground Radiates Heat**
Earth's surface loses heat to space`"]
s3["`**Temperature Drops**
Surface cools below dew point`"]
s4["`**Water Vapor Condenses**
Invisible vapor becomes visible droplets`"]
s1 --> s2
s2 --> s3
s3 --> s4Conditions for Dew Formation
Condition | Required State | Why Necessary |
|---|---|---|
Sky Condition | Clear night | Allows maximum heat radiation to space |
Wind Speed | Calm or light | Strong winds prevent surface cooling |
Humidity | High relative humidity | More water vapor available for condensation |
Surface Type | Good radiators | Grass, leaves cool faster than concrete |
Trap: Clouds absorb radiation — No, they reflect it back
Trap: Ground is colder on cloudy nights — Actually warmer due to reflected radiation
Trap: Wind deflection causes no dew — Wind prevents cooling, not deflection
Terrestrial Radiation & Heat Loss
Geography Earth's radiation Earth's surface
Terrestrial Radiation: Earth's Heat Loss Process
Earth radiates longwave infrared radiation after absorbing solar energy
Maximum radiation loss occurs on clear nights
Clouds act as natural blankets reflecting heat back
Terrestrial radiation is the Earth's way of losing heat gained during the day. The ground absorbs shortwave solar radiation and re-emits it as longwave infrared radiation, especially at night.
Clear vs Cloudy Night Radiation
Night Type | Radiation Pattern | Ground Temperature | Dew Formation |
|---|---|---|---|
Clear Night | Heat radiates freely to space | Rapid cooling | Dew forms |
Cloudy Night | Clouds reflect heat back | Slower cooling | No dew |
Radiation on Cloudy Nights
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Ground Emits Heat**
Longwave radiation moves upward`"]
s2["`**Clouds Intercept**
Water droplets absorb the radiation`"]
s3["`**Clouds Re-radiate**
Heat sent back down to Earth`"]
s4["`**Ground Stays Warm**
Less cooling than clear nights`"]
s1 --> s2
s2 --> s3
s3 --> s4Trap: Clouds absorb and keep radiation — They reflect it back
Trap: All radiation is blocked — Some escapes, but most is reflected
Trap: Only thick clouds prevent dew — Even thin cloud cover reduces cooling
Cloud-Radiation Interaction
Geography Clouds absorb Clouds reflect cloudy night
How Clouds Interact with Earth's Radiation
Clouds reflect back most terrestrial radiation like a blanket
Cloud greenhouse effect keeps nighttime temperatures higher
Water droplets in clouds are effective radiation reflectors
Clouds act as atmospheric blankets by intercepting Earth's outgoing longwave radiation and redirecting much of it back to the surface, creating a natural greenhouse effect.
Cloud Effects on Radiation
# Cloud-Radiation Interaction
## Daytime Effects
- Reflect solar radiation
- Cool surface temperature
- Higher albedo
## Nighttime Effects
- Reflect terrestrial radiation
- Warm surface temperature
- Greenhouse effect
## Physical Mechanism
- Water droplets absorb heat
- Re-emit in all directions
- Net downward radiationWhy Reflection, Not Absorption
Clouds absorb and re-emit radiation in all directions — net effect is reflection back to Earth
Water vapor is a strong greenhouse gas that traps longwave radiation
Thicker clouds create stronger radiation blanket effect
Even partial cloud cover reduces radiative cooling significantly
Trap: Clouds deflect wind — Wrong mechanism, it's about radiation
Trap: Ground is colder with clouds — Actually warmer due to trapped heat
Trap: Clouds absorb radiation completely — They reflect most of it back