PrecipitationPrecipitation

Chapter 16 Section 5

Pages 551-554

Chapter 16 Section 5

Pages 551-554

Precipitation

• Water evaporates into the air from every water surface on Earth and living things.

• Returns to Earth as a form of precipitation- any form of water that falls from clouds and reaches Earth’s surface.

Precipitation

• Comes from Clouds.– Not all clouds produce precipitation.

• Water Droplets grow by colliding and combining with other cloud droplets until they are heavy enough to fall.

How Precipitation Forms

Rain

• Most common form of precipitation.

• Must be .5mm in diameter.– Smaller= mist or drizzle.

• Fall from nimbostratus clouds.

Sleet

• Rain drops fall through a layer of air below 0°C (freezing point of water) and freeze into solid particles of ice (pellets).

• Smaller than .5mm in diameter.

• Water vapor in a cloud is converted directly into ice crystals (snowflakes).

• Have an endless number of shapes and patterns.

• All with six sides or branches.

• Join together to form larger clumps.

Snow

Freezing Rain

• Rain drops fall through the air and freeze when they touch a cold surface.

• Thick layers are heavy and can cause tree branches to break, power lines to fall.

• Makes sidewalks and roads slippery and dangerous.

Hail

• Larger than 5mm in diameter.

• Forms inside cumulonimbus cloud. (thunderstorm cloud)

• Causes damage to crops, buildings, and vehicles.

Hail

• Starts as an ice pellet inside a cold region of a cloud. Strong updrafts in the cloud cause the ice pellet to go up and down, adding a layer of ice each trip.

• Becomes heavy enough to fall.

Measuring Precipitation

• Rain gauge- an open ended can or tube that collects rainfall.– Has a funnel at the top to

increase the accuracy of the measurement.

• Snow fall- measured with a ruler or snow is melted and the depth is measured.

Controlling Precipitation

• Drought- long periods of low precipitation.

– Can damage crops. Which causes higher food prices.

– Can cause widespread hunger or famine.

Controlling Precipitation

• Cloud seeding- a method to produce rain during a drought.

• Dropping Frozen CO2 (Dry Ice) into clouds.– Causes water to start condensing on ice

crystals and to grow.

• Dropping Silver Iodide Crystals– Acts as artificial condensation nuclei

– Can be used to clear fog from an airport.