Clouds and Their Formation How do Clouds Form

Clouds and Their Formation

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

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.

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.

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).

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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.

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

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

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

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