Cloud Formation: A Guide to How Clouds Form in the Sky

1. Clouds and Their Formation

3. How do Clouds Form? • They form when air above the ground cools to its dew point. • There must be condensation nuclei present. • Examples of Nuclei: Pollen, Dust, Smoke, Volcanic Ash, Salt

4. Cloud Formation… • As the air rises due to convection, it cools at a rate of 10 degree Celsius for every 1 km in elevation. This rate of cooling is called the dry adiabatic lapse rate. • The cooling is caused only by the air expanding. • When the temperature of the rising air reaches the dew point, the humidity is then 100%, and condensation begins onto a nuclei.

6. Dew Point Lapse Rate • As the air rises the dew point also decreases but at a rate of 2 degrees Celsius per 1 km. This rate is called the Dew Point Lapse Rate. • Once the Dry Adiabatic Lapse rate and Dew Point Lapse rate are the same, condensation occurs. • Condensation needs a surface to stick to.

7. Cloud Formation… • As the water condenses onto nuclei, it releases heat (exothermic), and the lapse rate changes to 6 degrees Celsius per 1 Km. • The is called the moist-adiabatic lapse rate • The base of the cloud is known as the condensation level (temp. = dew point).

8. https://www.youtube.com/watch?v=UZEETyzql0Q

9. Another look…

10. Types of Cloud… • The type of cloud depends on how the air is moving. • If the air is moving horizontal, the clouds form in layers called stratiform clouds. • If the air movement is vertical, the clouds grow upwards, called cumuliform clouds.

11. Cirrus Clouds • Cirrus clouds are thin, feathery, and are made of ice crystals. • Average cloud height is 7000-13000 m.

12. Stratus Clouds • Stratus clouds are very low in altitude. • Alto status = 2,000 – 7,000 m • Stratus = 500 – 2,000 m

13. Cumulus Clouds • Cumulus clouds are formed by vertically rising air currents. They are thick, puffy, and massive.

15. https://www.youtube.com/watch?v=DjByja9ejTQ