16-4 Water in the Atmosphere

1. Describe humidity and how it is measured.2. Explain how clouds form.3. Name the three main types of clouds.

Introduction

Key Concept: Water is always moving between the atmosphere and Earth’s surface.

The water cycle is the movement of water between the atmosphere and Earth’s surface.

Water vapor enters the air through evaporation. Evaporation is when a liquid becomes a gas. Liquid water evaporates to become water vapor.

The water cycle includes all forms of precipitation, including rain and snow. Water moves from the atmosphere to Earth’s surface by precipitation.

Answer the following questions. Use your textbook and the ideas above.

1. Water moves between the atmosphere and Earth’s

surface through the cycle.

2. Circle the letter of the way that water enters the atmosphere.

a. evaporation

b. precipitation

c. condensation

Humidity (pages 561–562)

water

Key Concept: Relative humidity can be measured with an instrument called a psychrometer.

Humidity is a measure of how much water vapor is in the air. Warm air can hold more water vapor than cold air.

Relative humidity is a percentage measurement. Relative humidity is the percentage of water vapor in the air compared to how much humidity the air can hold.

A psychrometer is an instrument that measures relative humidity. A psychrometer has two thermometers. One thermometer has a wet cloth covering it. You can tell the relative humidity of the air by comparing the temperatures on the two thermometers.

Answer the following questions. Use your textbook and the ideas on page 263 and above.

1. Read each word in the box. In each sentence below, fill in the correct word or words.

a. An instrument that measures relative humidity is

a(an) .

b. The percentage of water vapor in the air compared to how much humidity the air can hold is

called .

c. A measure of how much water vapor is in the

air is called .

2. Circle the letter of each sentence that is true about a psychrometer.

a. A psychrometer has two thermometers.

b. One thermometer has a wet cloth covering it.

c. You compare the two thermometers to find out the relative humidity.

humidity

water vapor

psychrometer

relative humidity

psychrometer

Relative humidity

humidity

How Clouds Form (page 563)

2. Explain how clouds form.

Key Concept: Clouds form when water vapor in the air condenses to form liquid water or ice crystals.

Condensation is when a gas becomes a liquid. For example, water vapor condenses to form liquid water. This happens in the atmosphere when clouds form.

There are two things needed for condensation to occur in the atmosphere:

There must be cooling of the air.

There must be particles—tiny solids—in the air.

Cold air holds less water vapor than warm air. When air cools, water vapor condenses into little drops of water or ice crystals. The temperature at which this happens is called the dew point.

Tiny particles must be in the air for condensation of water to take place. Water needs something to condense onto.

Answer the following questions. Use your textbook and the ideas above.

1. The process in which a gas becomes a liquid is

called .

2. Circle the letter of each thing needed for condensation to occur in the atmosphere.

a. There must be particles in the air.

b. There must be cooling of the air.

c. There must be precipitation in the air.

3. Is the following sentence true or false? The temperature at which water vapor condenses into little

drops of water is called the dew point.

condensation

true

Types of Clouds (pages 564–566)

3. Name the three main types of clouds.

Key Concept: Scientists classify clouds into three main types based on their shape: cirrus, cumulus, and stratus. Clouds are further classified by their altitude.

Cirrus (SEER us) clouds are the wispy clouds that look like feathers in the sky. Cirrus clouds only form high in the sky.

Cumulus (KYOO myuh lus) clouds look like fluffy, rounded piles of cotton. Cumulus clouds can produce thunderstorms. Thunderstorm clouds are called cumulonimbus clouds.

Stratus (STRAT us) clouds are flat layers of clouds. Stratus clouds usually cover most of the sky. Stratus clouds that produce rain are called nimbostratus clouds.

Clouds that form near the ground are called fog. Fog often forms when the ground cools at night. Fog is common near bodies of water, such as a lake.

 

Answer the following questions. Use your textbook and the ideas above.

1. Draw a line from each type of cloud to its description.

Type of Cloud

cirrus clouds

cumulus clouds

stratus clouds

fog

Description

a. flat layers of clouds

b. clouds that form at or near the ground

c. clouds that look like fluffy, rounded piles of cotton

d. wispy clouds that look like feathers in the sky

1. Circle the letter of the type of cloud that often produces thunderstorms.

a. altocumulus

b. nimbostratus

c. cumulonimbus

2. The picture shows three types of clouds in the atmosphere. Draw a circle around the cumulus cloud.