Why Do Clouds Form? • Clouds need three things to form: • Cooling • Condensation Nuclei • Saturated Air
What Causes Cooling? There are Four Processes that lead to the cooling of air- • #1 Convective Cooling Rising air expands because pressure decreases Expansion causes the air to become cooler • Adiabatic Temperature Changesare changes in temperature from the expansion or compression of air
Adiabatic Temperature Change(Convective Cooling Continued) • For dry air, temperature changes 1ºC every 100 meters in elevation change • 5.4ºF for every 1000 feet • For moist air, the cooling rate varies from 0.5ºC per 100 m for air with a high moisture content to 0.9ºC per 100 m for air with a very low moisture content • Average is 0.7ºC per 100 m
Convective Cooling (Continued) • When the rising air reaches the dew point temperature, water vapor begins to condense • The condensation level is the height above the ground at which condensation takes place
#2 Forceful Lifting • An event occurs that forces the air to rise • Air moving up and over a mountain
#3Temperature Changes • Two air masses with different temperatures mix • The temperature change of the combined air masses may be cooler than the dew point
#4 Advective Cooling • Warm, moist air moving over cool land or water causes the air temperature to drop • Forms low clouds or fog
Condensation Nuclei • The water vapor needs a surface on which to condense. • Condensation nuclei are tiny, less than 0.001 mm in diameter. There MUST be solid particles in the air for the water vapor to condense onto. • Examples include: • Suspended particles of atmospheric dust • mineral particles • ash from fires • volcanic dust • microscopic organisms • vaporized meteors • salt from sea spray
Saturated Air • Air temperature must be equal to the dew point. • Thus, 100% humidity. . . Clouds form!
Let’s Make a Cloud! Magic?!. . . No, science.
Cloud Types 1 • Stratus Clouds • sheet-like, or layered. • Cumulus Clouds • puffy, like cotton balls. • Cirrus Clouds • thin and wispy.
Cloud Types 2 • High Clouds (above 6,000 m) • Cirrus • Cirrostratus • Mid-level Clouds • Altostratus • Altocumulus • Low-level Clouds • Stratus • Cumulus, Cumulonimbus