Water in the Atmosphere
Major Steps of the Water Cycle:
 The water cycle is the movement of
water between the atmosphere and
Earth’s surface.
 How does water vapor enter the air?
Evaporation/Transpiration
 Explain evaporation: The process by
which water molecules in liquid water
escape into the air as water vapor.
 The water vapor is now in the air and
forms clouds by condensation.
 How does water return to bodies of
water?
When water droplets become too large to
remain in the cloud, they fall to Earth as
precipitation. Water flows back to a body
of water – runoff.
Other terms to know:
 Transpiration - When plants release water
into the atmosphere.
 Runoff - precipitation water that runs
over land on its way back to a body of
water.
Details:
Evaporation (pg 54):
 An increase in energy (from solar
radiation), causes water molecules to
move faster, fast enough to change
matter from a liquid to a gas.
 Water (liquid) changes into water
vapor (gas).
 Warm air above the surface of the
Earth has molecules that are more
spread out (less dense), which means
there is room for more water vapor.
 This water vapor then rises with the
rising warm air during convection.
Condensation:
 The rising air during convection starts to
cool.
 Because the air molecules lose energy,
they start to slow down, move closer
together, and the air becomes more
dense.
 When the air cools, and becomes more
dense, there is no more room for water
vapor.
 The air is full or saturated and the water
vapor is forced out and condenses or
turns back into a liquid.
 The temperature at which condensation
begins is called the
dew point.
 What is needed for water vapor to
condense? (pg 57)
Tiny particles must be present so the
water has a surface to condense on.
 When water molecules condense on
particle, CLOUDS are formed.
Precipitation (pg 62):
 Eventually, clouds become very heavy, due to
all those clinging water drops.
 Precipitation is any form of water that falls from
clouds and reaches Earth’s surface.
 Describe the five types of precipitation:
1.Rain:
 Liquid water drops
 Most common kind of precipitation.
2.Sleet:
 Rain that passes through a layer of
below freezing air on its way to the
ground. Water drops freeze in ice.
3.Freezing Rain:
 Rain drops that freeze when they
touch a cold surface.
4.Snow:
 Water vapor converted directly into ice
crystals. Snowflakes have many
different shapes and patterns.
5.Hail:
 Forms inside cumulonimbus clouds
(thunderstorm clouds).
 Round pieces of ice formed when
frozen drops get blown back up into
the cloud combine, become heavy and
fall to the ground.