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Clouds The Recipe • Clouds need three things to form – Moisture – Cooling air to it’s Dew Point (condensation) – Condensation Nuclei (dust, smoke) How do we get to the Dew Point • The easiest way to bring an air masses temperature to it’s dew point is to move air to a higher altitude Cool As the moist air rises it’s temperature decreases and the water vapour begins to condense Warm Moist Air • The drier air is the farther it has to climb to reach it’s dew point • At higher altitudes the temperatures are much colder and below freezing Moist Air Dry Air • Moist air has more water vapour and will become saturated at a warmer temperature • As a result clouds will form at lower altitudes out of water droplets Moist Air • When the Dew point is below freezing this means that when the water vapour condense it will actually freeze into ice crystals • This usually happens at very high altitudes in dry conditions Moist Air Cloud types • Clouds can be classified in three different ways – Shape – Altitude – Is there precipitation? Cloud Shape • Cumulus – Puffy • Stratus – Shapeless – fog • Cirrus – Dry conditions – Ice crystals Cloud Height • Up to 2000 m – Just use cloud shape name • 2000 – 6000 m – Use prefix “alto” with the shape • 6000 m and above – Use prefix “cirro-” or suffix “-cirrus” with cloud shape – Example – altostratus or cirrostratus Precipitation • Precipitation – Use prefix “nimbo-” or suffix “nimbus” with the shape – Example - cumulonimbus Precipitation • The average drop is just 0.02 mm across in a cloud (too small to fall) • By the time it hits the ground the average drop is 2 mm across • So how does it grow? Growing by Coalesce • As the raindrop falls in the cloud it collides with other drops and begins to grow • Wind will continue to circulate the drop until it becomes to heavy and falls to the ground as precipitation