clouds power point

8/7/2019 Clouds Power Point

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Their formation and variations



� Collections of small water droplets or icecrystals that fall slowly through the air

� Ice crystals and water droplets form whencondensation or sublimation occurs more rapidlythan evaporation does



� Water vapor needs a solid surface to condenseon to form a cloud

� The troposphere is full of ice, salt, and dustparticles that are so small that they staysuspended in the atmoshpere

� These particles arecalled condensation

nuclei



� Steps of cloud formation

1. Rate of evaporation must be equal to rate ofcondensation

� When this occurs the air is ´saturatedµ with watervapor

2. Air temperature drops. This causes condensation to

occur faster than evaporation

3. Clouds form as a result of net condensation



� Four processes can cause air cooling:

� Adiabatic cooling

� Mixing

� Lifting

� Advective cooling



� The process by which the temperature of an airmass decreases as the air mass rises and expands

� Air mass rises atmospheric pressure decreases

molecules in air move farther apart results

in less collisions between molecules decreases

temperature of air mass



� Occurs when two bodies of moist air withdifferent temperatures mix

� Cloud formation may occur if the twocombined air masses cool enough



� Occurs when air is forced upward, whichresults in cooling

� Example: Mountains



� The process by which the temperature of an airmass decreases as the air moves over a coldsurface

� Example: ocean or land

� If the surface is colder than the air mass, thesurface will absorb heat from the air mass andthe air mass will cool



� There are three main types of clouds:

Stratus Cumulus

Cirrus



� Means sheet-like or layered

� Have a flat, uniform base and begin to form atvery low altitudes

� Cover large areas of the sky and often block outthe sun

� Variations:

� Nimbostratus: are dark and can cause heavyprecipitation

� Altostratus: form at middle altitudes, are thinner

than normal stratus clouds



� Means piled or heaped

� Low altitude, billowy clouds that commonlyhave a top that looks like cottons balls and a

flat, dark bottom

� Variations:

� Cumulonimbus: tall, dark cumulus clouds that canextend very high in the atmosphere, can have ananvil shaped top, produce thunderstorms

� Altocumulus: base begins at middle altitudes

� Stratocumulus: low clouds, combination of cumulusand stratus clouds



� Means curly

� Feathery clouds that are composed of icecrystals

� Form in the highest altitudes (above 6,000m)

� Variations:

� Cirrocumulus: rare, high-altitude, billowy,

composed entirely of ice crystals, indicate possiblesnow or rainfall

� Cirrostratus: long and thin, form a transparent veilin sky

clouds power point

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