Air Mass

Air Masses / Study Guide

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The Earth's atmosphere is very big and covers the whole Earth. This means that there are large bodies of air over the continents, oceans, and poles. When a large body of air stays over an area for a long time, it acquires some characteristics of that area and forms an air mass. An air mass is a large mass of air with similar properties throughout.

Multiple Choice

An air mass would have large differences in temperatures throughout.

Multiple Choice

Where would an air mass be most likely to form?

Multiple Choice

An air mass would most likely be able to form in

• a week

• an hour

• a minute

• a second

Air masses are defined mostly by their temperature and how much moisture, or water vapor, they contain. They get these properties from the areas on Earth they form over.

Multiple Select

Which two main characteristics define an air mass?

• oxygen level

• temperature

• water vapor

• color

• height

Air masses can move and they keep their characteristics for a period of time as they move around the Earth. Wind moves air masses. This wind might be near Earth's surface, or jet streams higher in the atmosphere.

Because air masses contain different levels of water vapor and temperature, they have a large effect on weather. Often, where two air masses meet, severe weather can form.

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Which is true after an air mass is moved into a new place?

• The air mass keeps its characteristics forever.

• An air mass keeps its characteristics for a while, but not forever.

• The air mass's characteristics change as soon as it moves.

Multiple Choice

You have been having many days of clear, sunny weather. Later in the afternoon, you see a row of storm clouds moving towards your town. What is most likely true?

• The air mass in your area is moving away, leaving an empty space in the atmosphere.

• A new air mass is approaching.

• The current air mass is creating storms in its middle.

Kinds of Air Masses

Air masses are defined using special names that tell about their temperature and amount of water vapor they contain.

An air mass that forms over the water in a warm area of Earth would be called a maritime tropical air mass.

Air masses are labeled based on where they form. Each type of air mass has a special label that helps identify it.

The first letter of an air mass's label tells whether it forms over water or land. This letter is always lowercase:

maritime (water) = m

continental (land) = c

The second letter of the label tells the temperature of the air mass and is always capitalized:

polar (cold) = P

tropical (warm) = T

arctic (very cold) = A

Multiple Choice

Water is to _______ air masses as land is to ________ air masses.

• continental; tropical

• tropical; continental

There are six main types of air masses. The graphic at right shows the maritime, or wet, air masses.

There are six main air masses. The image at right tells about the air masses that form over land.

Multiple Choice

Paul lives in a hot desert in the middle of a country. What type of air mass is most likely to form where Paul lives?

• maritime polar

• continental polar

• continental tropical

• maritime tropical

What is a Front?

When two air masses meet, a front is formed between them. A front is the boundary between two air masses. Most air masses move west to east across the United States, so fronts move in the same direction. However, fronts can also move back and forth over the same area. Some fronts do not move very much. These fronts are called stationary fronts.

Three common fronts are warm fronts, cold fronts, and stationary fronts. They can be marked on a map with different symbols. The triangles or half circles point in the direction the front is moving. If the symbols are alternating, it means the front is not moving, or is stationary.

When two fronts come into contact, weather like rain, snow, and thunderstorms often forms. Fronts are named by the type of air moving into the area.

Warm fronts bring warm air into an area. When a warm front meets a cold front, the warm air travels up and over the cold air. This can cause rain or snow to form.

Warm fronts usually cause clouds to form high in the atmosphere. People can usually see the clouds before they feel the warm air brought by the warm air mass behind the warm front.

Cold fronts bring cold air into an area. When a cold front meets a warm front, the cold air forces warm air to move up quickly. This often leads to the formation of severe storms or heavy precipitation.

Cold fronts usually form clouds right at their boders. People usually see the clouds and feel the cold air at about the same time as the cold front ahead of a cold air mass arrives.

Multiple Choice

Both cold and warm air fronts have rising ______ air.

• cool

• warm

Multiple Choice

You are outside on a nice day. You see clouds approaching very quickly and as they reach you, the temperature changes almost at the same time. What type of front has moved into the area?

• cold front

• warm front

Multiple Select

Select the types of weather that can be caused by a warm or cold front.

Multiple Choice

What is an air mass?

• a large mass of air with similar properties throughout

• rising and sinking of gases, liquids, or solids in a circular path

• the gases that surround the Earth

• the pushing force that air exerts on an area

Multiple Choice

A front is _______.

• the gases that surround the Earth

• the pushing force that air exerts on an area

• the boundary between two air masses

• rising and sinking of gases, liquids, or solids in a circular path

Multiple Choice

An astronaut is studying the atmosphere of a planet in a new solar system. There seems to be large areas of the planet with warm air and others with cold air. These areas also have different levels of water vapor in them. What would be the best word to describe these areas on the planet?

• cold fronts

• jet streams

• air masses

• maritime air

Multiple Select

Which are true about air masses? Check all that are true

• They are defined by their temperature and mositure.

• They cannot move.

• They lose their characteristics as soon as they move locations.

• They form over very large areas.

Multiple Choice

What type of air mass is shown below? Click on the image at left to enlarge.

• continental tropical

• maritime tropical

• continental polar

• maritime arctic

• maritime polar

Multiple Choice

What do all continental air masses have in common?

• They have the same temperatures.

• They do not form fronts.

• They are all the same exact size.

• They are drier than maritime air masses.

Multiple Choice

It has been sunny and clear, but the weather forecast calls for stormy weather and low temperatures next Wednesday. What type of front is most likely going to move through the area on that day?

• a warm front

• a cold front

• a stationary front

• all of the above