EXIT CHAPTER

1818CHAPTER

18.1 Humidity and Condensation

18.2 Clouds

18.3 Precipitation

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Water in the Atmosphere

DEPOSITION (Heat released)

FREEZING CONDENSATION

MELTING EVAPORATION

LIQUID WATER(clouds, rain, dew)

ICE(snow, hail, frost)

WATER VAPOR(invisible)

SUBLIMATION (Heat absorbed)

Heat released

Heat absorbed

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Water exists in the atmosphere as a solid, a liquid,

and a gas.

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VOCABULARY18.1 Humidity and Condensation

1818 Water in the Atmosphere

Evaporating water absorbs heat from the

surroundings, which become cooler. Condensing

water releases heat to the surroundings.

water vapor

condensation

specific humidity

saturated

relative humidity

dew point

condensation nuclei

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Humidity is the measure of water vapor in the air.

Warmer air can contain more water vapor, while

cooler air can contain less.

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Fog and clouds form when air is cooled to its dew

point and water in the air condenses on

condensation nuclei. Dew or frost forms if air cools to

the dew point upon contact with cold ground and the

water vapor condenses directly on the ground.

18.1 Humidity and Condensation1818 Water in the Atmosphere

water vapor

condensation

specific humidity

saturated

relative humidity

dew point

condensation nuclei

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Clouds are classified by their height above ground

and their shape. The main types of clouds are stratus

(layered, low clouds), cumulus (fluffy clouds with flat

bases), and cirrus (high, feathery ice clouds).

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VOCABULARY18.2 Clouds

1818 Water in the Atmosphere

Cirrus

StratusCumulus

Cumulonimbus

Cumuliform clouds are formed by rising air, and stratiform clouds form in horizontal layers.

stratus

cumulus

cirrus

condensation level

dry-adiabaticlapse rate

moist-adiabaticlapse rate

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Rising air cools at the dry-adiabatic lapse rate with

no condensation, and at the moist-adiabatic lapse

rate with condensation.

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VOCABULARY18.2 Clouds

1818 Water in the Atmosphere

Heat released through condensation within a cloud

can cause air within the cloud to rise to great

heights.

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stratus

cumulus

cirrus

condensation level

dry-adiabaticlapse rate

moist-adiabaticlapse rate

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Water droplets in clouds grow by colliding with each

other.

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VOCABULARY18.3 Precipitation

1818 Water in the Atmosphere

Ice crystals grow from collisions and by using water vapor that evaporated from super-cooled drops.

Growth of a Raindrop

The forms of precipitation include drizzle, rain, sleet, snow, freezing rain, and hail.

precipitation

sleet

freezing rain

hail

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Precipitation’s type depends on the conditions as it

forms and falls. Precipitation falls in regions where

moist air tends to rise, producing condensation.

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VOCABULARY18.3 Precipitation

1818 Water in the Atmosphere

Less than 25

25 to 50 100 to 250

50 to 100 More than 250

Mean Annual Precipitation (cm)

Cold air sinks near the North Pole. This area is dry.

Cold air sinks near the South Pole. This area is dry.

Air near the equator rises. Equatorial areas are usually wet.

The leeward side of the Andes Mountains are dry.

The windward side of the Andes Mountains are wet.

precipitation

sleet

freezing rain

hail

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1818 Water in the Atmosphere

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