Earth and Space Science / Unit 7: The Atmosphere and Weather
7.4 Humidity and Clouds
Notes
Humidity is water vapor in the air.
- Relative humidity $\displaystyle = \frac{\text{vapor present}}{\text{max vapor air can hold}} \times 100\%$. Warm air holds more vapor.
- The dew point is the temperature at which air becomes saturated (100% relative humidity). Cooling air to the dew point causes condensation.
- Clouds form when rising air cools and vapor condenses on dust particles.
- Types: cirrus (high, thin, wispy), cumulus (puffy, fair weather), stratus (flat layers), cumulonimbus (towering storm clouds).
- Example: air holding 10 g/m³ when it could hold 20 g/m³ has relative humidity 50%.
Practice
Air holds 12 g of water vapor per cubic meter and could hold 24 g. Its relative humidity is:
$12 \div 24 = 0.5$.
Clouds form when air:
Condensation needs cooling to saturation.
Towering clouds producing thunderstorms are:
Cumulonimbus clouds have strong updrafts.
Ready for more? Take the Unit 7 test.