Miss Nelson

SCIENCE ~ CHAPTER 8

WEATHER

Water in the Atmosphere

SECTION 1

What happens to the mirror in your bathroom when you take a hot

shower?

ANTICIPATORY SET

What happens to the mirror in your bathroom when you take a hot shower?

Warm, moist air from the shower comes in contact with cool surface of the mirror.

The air cools and can hold less water vapor. As a result, water vapor condenses on the

mirror.Clouds form in the same way!

ANTICIPATORY SET

S 6.4.e –Students know differences in pressure, heat, air movement, and humidity result in change in weather

STANDARDS

What is humidity and how is it measured?

How do clouds form?

What are the three main types of clouds?

THE BIG IDEA

Water cycle – the continual movement of water among Earth’s atmosphere, oceans, and land through evaporation, condensation, and precipitation

Evaporation – the process by which water molecules in l iquid water escape into the air as water vapor

Humidity – the amount of water vapor in a given volume of air

Relative humidity - the percentage of water vapor in the air compressed to the maximum amount of water vapor that air can contain at a given temperature

Psychrometer – an instrument used to measure relative humidity, consisting of a wet-bulb thermometer and a dry-bulb thermometer

KEY TERMS

Condensation – the process by which molecules of water vapor in the air become liquid water

Dew point – the temperature at which condensation begins

Cirrus – wispy, feathery clouds made mostly of ice crystals that form at high levels

Cumulus – fl uff y, white clouds, usually with fl at bottoms that look like rounded piles of cotton

Stratus – clouds that form in fl at layers and often cover much of the sky

KEY TERMS

View the diagram on page 301 of your textbook

Read Water in the Atmosphere on page 300 of your textbook

THE WATER CYCLE

Humidity is a measure of the amount of water vapor in the air

Air’s ability to hold water vapor depends on its temperature

Warm air = more water vapor than cool air

HUMIDITY

Weather reports usually refer to the water vapor in the air as relative humidity

Relative humidity is the percentage of water vapor that is actually in the air compared to the maximum amount of water vapor the air can hold at a particular temperature

Air with a relative humidity of 100 percent is said to be saturated

RELATIVE HUMIDITY

Relative humidity can be measured with an instrument called a psychrometer

MEASURING RELATIVE HUMIDITY

Read Humidity on pages 301-302 of your textbook

HUMIDITY

Clouds form when water vapor in the air condenses to form liquid water or ice crystals

Process is called condensation

HOW CLOUDS FORM

Two conditions are required for condensation:

Cooling of the airPresence of particles in the air

HOW CLOUDS FORM

As air cools, the amount of water vapor it can hold decreases

The water vapor condenses into tiny droplets of water or ice crystals

The temperature at which condensation begins is called the dew point

Dew point above freezing = water dropletsDew point below freezing = ice crystals

THE ROLE OF COOLING

For water vapor to condense, tiny particles must be present

The water vapor needs a surface on which to condense

In cloud formation, most of these particles are:Salt crystalsDust from soilSmoke

THE ROLE OF PARTICLES

Scientists classify clouds into three main types based on their shape:CirrusCumulusStatus

Clouds are further classified by their altitude

TYPES OF CLOUDS

Wispy, feathery clouds

Comes from the word meaning “a curl of hair”

Form only at high levels where temperatures are very low

As a result, are made of ice crystals

Have feathery “hooked” ends

Look like the scales of a fish

CIRRUS CLOUDS

Look like fluffy, rounded piles of cotton

Word means “heap” or “mass” in Latin

Usually indicate fair weather

When you add the suffi x –nimbus, which means “rain,” you get clouds that produce thunderstorms

CUMULUS CLOUDS

Form in flat layers

Strato means “spread out”

Usually cover most of the sky

Are a uniform, dull, gray color

As they thicken they produce rain or snow

Called nimbostratus clouds

STRATUS CLOUDS

Part of a cloud’s name may be based on its height

Clouds that form between 2-6 kilometers above the surface have the prefix alto- (means high)

Altocumulus and altostratus are the two main types of these clouds

ALTOCUMULUS AND ALTOSTRATUS

Clouds that form near the ground are called fog

Often forms when the ground cools at night after a warm, humid day

More common near bodies of water or low-lying marshy areas

FOG

Read Types of Clouds on pages 304 – 306 of your textbook

TYPES OF CLOUDS

What is humidity?

How is it measured?

CHECK FOR UNDERSTANDING

What is humidity?Humidity is a measure of the amount of water vapor in the air.

How is it measured?Humidity is measured using “relative humidity,” which is the percentage of water vapor that is actually in the air compared to the amount of water vapor the air can hold at a particular temperature. Relative humidity can be measured using a psychrometer.

CHECK FOR UNDERSTANDING

How do clouds form?

What are the three main types of clouds?

GUIDED PRACTICE

How do clouds form?Clouds form when water vapor in the air condenses to form liquid water or ice crystals.

What are the three main types of clouds?The three main types of clouds are cirrus, cumulus, and stratus.

GUIDED PRACTICE

Complete Weather 8-1 Independent Practice

INDEPENDENT PRACTICE