• Precipitation is any
form of water that falls from clouds and reaches Earth's surface.
–
Cloud droplets or ice crystals must grow heavy enough to fall through the air.
– Droplets grow by colliding and
combining with other cloud droplets.
– When
heavy enough, they fall out of the cloud as raindrops.
•
Common types of precipitation include:
–
Rain
•
Most common type of precipitation
•
Rain = 0.5 mm in diameter
•
Smaller drops are called drizzle or mist
•
Common types of precipitation include:
–
Sleet
•
Ice particles smaller than 0.5 mm in diameter
•
Forms when raindrops fall through a layer of freezing air and turn into solid ice particles.
• Common types of precipitation
include:
– Freezing
Rain
• Forms
when raindrops freeze on a cold surface.
•
Thick layers of ice may form, causing damage to tree branches and power lines.
• Common types of precipitation
include:
– Hail
(Hailstones)
• Pellets
of ice larger than 5 mm
•
Forms only inside cumulonimbus clouds during a thunderstorm.
–
Strong updrafts in the cloud carry the hailstone up and down through the cold region many times, adding
a new layer of ice.
– It eventually
falls when it becomes too heavy for the updraft.
•
Common types of precipitation include:
–
Snow
•
Forms when water vapor in a cloud is converted directly into ice crystals
•
Each snowflake has six sides.
•
Measuring Precipitation:
– Meteorologists
measure rainfall with a rain gauge.
•
Rain gauge = open-ended can or tube that collects rainfall.
•
Rain is measured by dipping a ruler into the water or by reading a marked scale.
• Snowfall is measured
by using a ruler or by melting collected snow and measuring the depth of water it produces.
–
On average, 10 cm of snow = 1 cm of rain
•
Drought
– Drought
is a long period of low precipitation.
– Cause
crops to fail which producing widespread hunger, or famine.
–
Prevention?
•
Cloud seeding = dropping tiny crystals of dry ice and silver iodide from airplanes.
• Water vapor can condense
on the particles of silver iodide, forming rain or snow.
•
The dry ice cools the droplets so they can condense without particles.