MOISTURE IN THE ATMOSPHERE Advanced Earth Science

CLOUD FORMATION  1. Clouds form as warm air moves upward and cools to its dew point  2. The water vapor in air condenses into tiny droplets  3. Droplets condense around small particles called condensation nuclei  4. When millions of these droplets collect, a cloud is formed

CLOUD FORMATION  Orographic Lifting  Wind encounters a mountain and air has nowhere to go but upward  Air cools and moisture condenses forming clouds/precipitation

CLOUD FORMATION  Collision  Two air masses of different temperature meet  Warm air is forced to rise over the more dense, cold air  Warm air cool and water vapor condenses to form clouds  Can cause thunderstorms

STABILITY  The ability of an air mass to resist rising  Cool air can resist rising – it is stable  Warm, rising air - unstable

LATENT HEAT  Energy stored in water vapor  Released into the air when condensation occurs  When latent heat is released and warms the air it provides energy to a weather system, which can increase its intensity

CLOUD CLASSIFICATION - HEIGHT  Low – Strato - Below 2000m  Medium – Alto - Base between m  High – Cirro - Bases start above 6000m

CLOUD CLASSIFICATION - SHAPE  Stratus – smooth, even sheets or layers at low altitudes  Cumulus – puffy, white clouds, often with flat bases  Cirrus – high, thin, white, feathery clouds made of ice crystals  Nimbus – very dark and full of water, sunlight cannot penetrate

CLOUDS OF VERTICAL DEVELOPMENT  If air that makes up a cumulus cloud is unstable, the cloud will be warmer than surrounding air and continue to grow  Clouds can grow through middle altitudes and if conditions are right they can reach nearly 18,000m and the tops of the cloud will form ice crystals  Capable of producing torrential rains and strong winds.

PRECIPITATION  Cloud droplets collide and form larger droplets = coalescence  Eventually, drops become too heavy, gravity takes over, and the droplet falls  Air temperature determines whether droplets form as rain, snow, sleet, or hail

PRECIPITATION – SLEET & HAIL FORMATION  When precipitation forms at cold temperatures, it takes the form of ice crystals or snow  Convective currents can carry the droplets up and down through freezing and non-freezing air forming ice pellets (sleet)  If the convective motion is especially strong it can form very large pellets (hail)

WATER CYCLE  The constant movement of water between the atmosphere and Earth’s surface  Energy received from the Sun causes liquid water to change into gas (evaporation)  As water vapor rises, it cools and changes back into a liquid (condensation)  Water droplets in clouds combine and fall back to Earth’s surface (precipitation)