Download water cycle notes

The Water Cycle
Water in the Atmosphere
The movement of water between the atmosphere and Earth is known as the water cycle.
-
Water vapor enters the air by evaporation from bodies of water
1.) Evaporation – the process by which water molecules in liquid water escape into the air
as water vapor
a. Water vapor can be also added to the air by:
i. Living things – water enters the roots of plants, rises to the leaves, and is
released as vapor
b. Humidity – a measure of the amount of water vapor in the air
i. Air’s ability to hold water vapor depends on its temperature; warm air
can hold more vapor than cool air
2.) Condensation – the process of molecules of water vapor in the air becoming liquid water
a. Clouds form when water vapor in the air condenses to form liquid water or ice
crystals
b. Cloud formation also requires tiny particles for water to “stick” to (salt crystals,
soil dust, smoke)
i. 2 conditions are required for condensation:
1. Cooling of the air
2. The presence of particles in the air
ii. Dew point – temperature at which condensation begins
Types of Clouds
1.) Cirrus – wispy, feathery clouds
a. Form at high levels (@ 6 km/3.25 mi) where temps are low
b. Made of ice crystals
Other forms include: cirrocumulus
2.) Cumulus – fluffy, rounded piles of cotton
a. Form less than 2 km/1 mi above ground
b. Can grown in size and height as high as 18 km/11 mi
c. If not tall = nice weather (common on sunny days)
d. Towering clouds w/ flat tops (cumulonimbus) = thunderstorms
Other forms include: altocumulus
3.) Stratus – flat layer clouds
a. Usually cover most of sky
b. Dull, gray color
c. If they thicken = cause drizzle, rain, or snow (nimbostratus)
Other forms include: altostratus (high clouds)
Fog – clouds that form at or near the ground
Water in the Atmosphere (Cont.)
3.) Precipitation – any form of water that falls from clouds and reaches Earth’s surface.
 Not all clouds produce precipitation
 Droplets/ice crystals need to grow heavy enough to fall
i. Droplets can grow by colliding and combining w/ other
droplets
ii. As they get bigger, they move faster & collect smaller
droplets (raindrops fall once they’re heavy enough)
Types of Precipitation
1.) Rain –
a. most common form of precipitation
b. smaller drops are called drizzle; even smaller is called mist (both from
stratus clouds)
2.) Sleet –
a. Raindrops that fall through a layer of air below freezing pt of water
(0˚C/32˚F)
b. As they fall, they freeze into solid particles of ice
3.) Freezing Rain –
a. Raindrops that fall through cold air near the ground (don’t freeze in air)
b. Ice storms can occur (a thick layer of ice builds up on every surface)
4.) Snow –
a. Water vapor in clouds is converted directly into ice crystals (snowflakes)
5.) Hail –
a. Round pellets of ice larger than 5 mm in diameter are hailstones
b. Only forms inside cumulonimbus clouds during thunderstorms
c. Strong updrafts (wind) carry hail up through cold temps many times; new
layers of ice form around it each time making it larger until it’s heavy
enough to fall to the ground
d. Can cause lots of damage
4.) Collection/Surface Runoff:
When water falls back to Earth as precipitation, it may fall back in the oceans, lakes, rivers, or
streams. Sometimes it ends up on land and soaks into the Earth. This water gets used by plants
and animals that drink it. Other times it runs over the land and heads back into larger bodies of
water (runoff).