Latent heat
Also called: Latent heat of vaporisation, Latent heat of condensation · Topic: Water in the Atmosphere: Humidity, Condensation, Clouds and Precipitation · NCERT: Class 11, Ch 8 "Solar Radiation, Heat Balance and Temperature"; Class 11, Ch 10 "Water in the Atmosphere"
Meaning
Latent heat means "hidden heat". It is the heat water takes in when it evaporates. The temperature does not rise, because the heat is stored in the vapour. Near 0 °C it is about 2,500 joules per gram. The same heat is released when the vapour condenses into droplets. In this way latent heat carries energy from the Earth's surface up into the air. It makes up 19 of 100 units in the heat budget. Related forms are the latent heat of fusion (melting and freezing) and the latent heat of sublimation (vapour turning straight into ice).
Example
Tropical cyclones over the Bay of Bengal draw huge amounts of vapour from the warm sea. When this vapour condenses in towering clouds, the latent heat released drives the storm's strong winds and heavy rain.
Don't confuse with
- Sensible heat: this is heat you can feel and measure as a change in temperature. Latent heat changes the state of water without changing its temperature.