Dew
Topic: Water in the Atmosphere: Humidity, Condensation, Clouds and Precipitation · NCERT: Class 11, Ch 10 "Water in the Atmosphere"
Meaning
Dew is water droplets that form directly on cool surfaces such as grass, leaves and stones. It does not form on particles floating in the air. At night the ground loses heat and the air touching it cools to its dew point. The dew point must be above freezing, so the vapour turns into liquid drops. Dew forms best with:
- clear skies;
- calm air;
- high relative humidity;
- long, cold nights.
Example
On clear winter mornings in the plains of Uttar Pradesh, lawns and crop leaves are wet with dew even though no rain has fallen.
Don't confuse with
- Frost: it forms in the same clear, calm conditions, but when the dew point is at or below 0 °C. The vapour then turns into ice crystals, not water drops.
- Fog: its droplets float in the air on dust, smoke or salt particles. Dew forms on solid surfaces.