Table of Contents

6.3

Masses and Their Movements

Weather Patterns

Vocabulary 6.3

1. Air mass: A huge body of air that has similar temperature, humidity, and air pressure at any given time.

2. Maritime A humid air mass that forms over oceans.

3. Continental A dry air mass that forms over land.

4. Tropical: A warm air mass that forms in the tropics and has low pressure.

5. Polar: a cold air mass that forms 50 degrees north latitude or south latitude of 50 degrees south latitude and has high air pressure.

6. Jet Stream- bands of high-speed winds about 10 km above Earth’s surface.

7. Front- The boundary where unlike air masses meet but do not mix.

8. Occluded- Cut off, as in a front where warm air mass is caught between two cooler air masses.

9. Cyclone- A swirling center of low-pressure air.

10. Anticyclone- A high-pressure center of dry air.

(Prefix anti= opposite of)

What are the Major Air Masses?

An air mass is a huge body of air in the lower atmosphere that has similar temperature, humidity, and air pressure at any given height.

Four major types of air masses influence the weather in North America:

• maritime tropical• continental tropical• maritime polar• continental polar.

temperature

Characteristics of an air mass:

humidity

Major Air Masses

Maritime air masses form over the ocean and can be very humid.

Continental air masses form over land, and are drier than maritime air masses.

Tropical air masses are warm, form in the tropics, and have low air pressure.

Polar air masses are cold, form near the poles, and have high air pressure.

In North America, most air masses move from WEST to EAST

Air Masses and Their Movements

Types of Air Masses

Air masses can be classified according to temperature and humidity.

North American Air MassesAir masses can be warm or cold, and humid or dry.

Air Masses and Their Movements

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What Are the Major Air Masses? Pg. 203

How Air Masses Move type of air mass (cold/warm)

• When air masses interacts with other air masses, it causes the weather to change.

• In the U.S., air masses are moved by prevailing westerlies and jet streams.

The ___________ ____________, the major wind belts over the continental U.S. push air masses from west to east.

The jet stream is a band of _______-_______ wind about 10 kilometers above the surface of Earth that pushes air masses along. (within Prevailing winds)

Fronts (The boundary where air masses meet but do not mix) occur along the boundaries between air masses.

Changeable weather develops along fronts.

What Are the Main Types of Fronts? Pg.204

Air masses collide and can form four types of fronts:

cold front , warm front, stationary front ,occluded fronts

When a faster cold air mass runs into a slower warm air mass, a cold front forms. The cold air slides under the warm air. As the warm air rises, it cools and condenses, often resulting in heavy rain or snow.

When a faster warm air mass runs into a slower cold air mass, a warm front forms. The warm air slides up over the cold air, possibly causing light rain or snow.

direction the move

temperatureThe characteristic of front depends on:

What Are the Main Types of Fronts? Pg.205

• When a cold air mass and warm air mass collide, but neither displaces the other, a stationary front occurs. Water vapor in the warm air condenses into rain, snow, fog, or clouds, lingering for days.

• When a warm air mass is caught between two cooler air masses, the warm air is pushed up and an occluded front forms. (The warm air mass is cut off, or occluded, from the ground.) Temperatures at the ground get cooler, and it may get cloudy and rain or snow.

Types of FrontsWhat type of weather is brought by each front?

Air Masses and Their Movements

What Weather Do Cyclones and Anticyclones Bring? Pg. 206

swirling center of low-pressure air is called a cyclone. In the Northern Hemisphere, cyclones spin counterclockwise when viewed from above. Cyclones and decreasing air pressure are associated with clouds, wind, and precipitation.

An anticyclone is the opposite of a cyclone. The descending air in an anticyclone generally causes dry clear weather

Cyclones and AnticyclonesWhich image is a cyclone and which is an anticyclone?

What is the air motion direction of each?

Air Masses and Their Movements

Air Masses and Their Movements

Which circles are low-pressure centers and which are high-pressure centers?

Cloud TypesThere are many different types of clouds.

Clouds

Cirrus

Cumulonimbus

Fog

Cumulus

Altocumulus

Altostratus

Cirrocumulus

Nimbostratus

Stratus