The Atmosphere

Chapter 16 Section 1

The Water Cycle• The water cycle is a continuous movement of water

from water sources, such as lakes and oceans• Condensation occurs when water vapor cools and

changes back into liquid droplets (cloud formation)• Evaporation occurs when liquid water changes into

water vapor (Gas)• Transpiration is the process by which plants release

water vapor into the air through their leaves• Precipitation occurs when rain, snow, sleet, or hail falls

from clouds onto the Earth’s surface• Runoff is water, that flows across land into rivers, lakes

and oceans Water Cycle Quiz

Humidity• Humidity is the amount of water vapor or moisture

in the air• Relative humidity is the amount of moisture the air

contains compared with the maximum amount it can hold at a particular temperature

• Suppose that 1 m3 of air at a certain temperature can hold 20 g of water vapor. However, you know that the air actually contains 5 g of water vapor. What is the relative humidity?

The Process of Condensation• Condensation is the process by which a gas, such as

water vapor, becomes a liquid.• Condensation occurs when the air next to a glass

cools below its dew point• Dew point is the temperature to which air must cool

to be completely saturated• Before water vapor can condense it must have a

surface to condense on

Clouds• Clouds are a collection of millions of tiny water

droplets or ice crystals• High clouds are cold do to the high altitude, high

clouds are made up of ice crystals, prefix (cirro-)• Middle clouds can be made up of water droplets or

ice crystals, prefix (alto-)• Low clouds are made up of water droplets, prefix

(strato-)• Cumulus clouds are puffy, white clouds that tend to

have flat bottoms

Clouds• Stratus clouds form in layers that cover large areas

of the sky• Cirrus clouds are thin, feathery, white clouds found

at high altitudes

Precipitation• Precipitation is water, in solid or liquid form, that

falls from the air to the Earth• There are four major forms of precipitation rain,

snow, sleet, and hail• Rain is the most common form of precipitation• Snow is the most common form of solid

precipitation• Snow forms when temperatures are so cold that

water vapor changes directly to a solid• Sleet, also known as freezing rain, forms when

rain falls through a layer of freezing air

Precipitation• Hail is a solid precipitation that falls as balls or

lumps of ice • Up drafts of air in the clouds carry raindrops to

high altitudes in the cloud, where they freeze