Air Masses Air Masses and Frontsand Fronts

What are the four types of air What are the four types of air masses?masses?

Maritime TropicalMaritime Tropical Maritime PolarMaritime Polar Continental TropicalContinental Tropical Continental PolarContinental Polar

Maritime TropicalMaritime Tropical

• Warm humidWarm humid air air masses from oceans masses from oceans near the tropics.near the tropics.

• They form over the Gulf They form over the Gulf of Mexico and the of Mexico and the Atlantic Ocean.Atlantic Ocean.

• In the summer time In the summer time maritime tropical maritime tropical usually bring hot humid usually bring hot humid weather.weather.

• In winter, a humid air In winter, a humid air mass can bring heavy mass can bring heavy rain or snow.rain or snow.

Maritime PolarMaritime Polar

Cool humidCool humid air air masses form over the masses form over the icy cold North Pacific icy cold North Pacific and North Atlantic and North Atlantic oceans.oceans.

The air masses affect The air masses affect the west coast more the west coast more than the east coast.than the east coast.

In the summer they In the summer they often bring rain, fog, often bring rain, fog, and cool temperatures and cool temperatures to the west coast.to the west coast.

Continental TropicalContinental Tropical

Hot dryHot dry air masses air masses form only in the form only in the summer over dry summer over dry areas of southwestern areas of southwestern and northern Mexico.and northern Mexico.

Cover a smaller area Cover a smaller area than other air masses.than other air masses.

Bring hot, dry Bring hot, dry weather to the south.weather to the south.

Continental Polar Form over central and

northern Canada and Alaska.

Bring cool and cold air. In winter they bring

clear, cool, and dry air to most of northern America.

In the summer, storms may occur when continental air masses move south and meet maritime tropical that move north.

FrontsFronts When air masses meet When air masses meet

is a front, the collision is a front, the collision often causes storms often causes storms and weather changes.and weather changes.

A front may be 15 to A front may be 15 to 200 kilometers wide 200 kilometers wide and extend as much as and extend as much as 10 kilometers up to the 10 kilometers up to the troposphere.troposphere.

The kind of front that The kind of front that develops depends on develops depends on the characteristics of the characteristics of the air masses and how the air masses and how they move.they move.

There are four types of There are four types of fronts.fronts.

Cold Fronts.Cold Fronts. Warm Fronts.Warm Fronts. Stationary Fronts.Stationary Fronts. Occluded FrontsOccluded Fronts..

Cold FrontsCold Fronts Cold air is dense and tends to Cold air is dense and tends to

sink.sink. Warm air is less dense and Warm air is less dense and

tends to rise.tends to rise. When a moving cold air mass When a moving cold air mass

runs into a slowly moving runs into a slowly moving warm air mass, the denser warm air mass, the denser cold air slides under the cold air slides under the warmer air.warmer air.

Warm air can hold more Warm air can hold more water vapor than cool air.water vapor than cool air.

If there is a lot of water If there is a lot of water vapor in the warm air heavy vapor in the warm air heavy rain or snow may fall.rain or snow may fall.

Cold fronts move quickly so Cold fronts move quickly so they can cause weather they can cause weather changes.changes.

After a cold front passes, After a cold front passes, cool, dry air moves in.cool, dry air moves in.

Warm Fronts

A moving warm air mass collides with a slowly moving cold air mass.

If the warm air is humid showers and light rain might. fall along the front where the warm and cold air meet.

If the warm air is dry scattered clouds may form.

After a warm front passes through an area the weather is likely to be warm and humid.

Winter warm fronts bring snow.

Stationary FrontsStationary Fronts Sometimes cold and Sometimes cold and

warm air masses meet warm air masses meet but neither one has but neither one has enough force to move.enough force to move.

Where the warm and Where the warm and cold air meet, water cold air meet, water vapor in the warm air vapor in the warm air turns into rain, snow, turns into rain, snow, fog, or clouds.fog, or clouds.

Occluded Fronts

A warm air mass is caught between two cooler air masses.

As warm air cools and its water vapor condenses, the weather may turn cloudy, rainy, or snowy.

Cyclones and AnticyclonesCyclones and Anticyclones

As warm air at the center of a cyclone As warm air at the center of a cyclone rises , the air pressure decreases.rises , the air pressure decreases.

Winds in a cyclone spin counterclockwise Winds in a cyclone spin counterclockwise in the Northern Hemisphere.in the Northern Hemisphere.

As air rises in a cyclone the air cools As air rises in a cyclone the air cools forming clouds and precipitation.forming clouds and precipitation.

Winds spiral outward from the center of Winds spiral outward from the center of an anticyclone, moving towards areas of an anticyclone, moving towards areas of low pressure.low pressure.

Winds in an anticyclone spin clockwise in Winds in an anticyclone spin clockwise in the Northern Hemisphere.the Northern Hemisphere.

CyclonesCyclones

Hurricanes are very Hurricanes are very large cyclones that large cyclones that can cause can cause widespread damage.widespread damage.

                                                         

                                        

AnticyclonesAnticyclones

Air flows clockwise Air flows clockwise around a high-around a high-pressure system in pressure system in the northern the northern hemisphere. hemisphere.

Air tends to sink near Air tends to sink near high-pressure high-pressure centers, which centers, which inhibits precipitation inhibits precipitation and cloud formation. and cloud formation.

Homework

Choose an air mass or frontal system. Write a brief description of how that would affect their activities/plans for that day.

(HALF A PAGE)

Vocabulary

Air mass- a huge body of air that has similar temperature, humidity, and pressure.

Tropical- or warm air masses form in the tropics and have low air pressure

Polar- or cold air masses from North of 50o N latitude and South of 50o S latitude.

Maritime- air masses that form over oceans Continental- air masses form over land in the

middle of continents and are dry. Front- the area where the masses meet and do not

mix. Occluded- the warm air masses is cut off. Cyclone- a swirling center of low air pressure. Anticyclone- area of high pressure centers of dry

air.

Section 1 Review

1.) What two main characteristics are used to classify air masses?

Temperature Humidity

Section 1 Review

2.) What's a front? Name and describe the four fronts. Front- the area where the masses meet but do not

mix. Cold Fronts- when a rapidly moving cold air mass

runs into a slowly moving air mass, the denser cold air slides under the lighter warm air.

Warm Fronts- a moving warm air mass collides with a slowly moving cold air mass.

Stationary Fronts- sometimes cold and warm air masses meet but neither one has enough force to move.

Occluded Fronts- a warm air mass is caught between two cooler air masses.

Section 1 Review

3.) What is a cyclone? What kind of weather does it bring?

Cyclone- a swirling center of low air pressure.

A cyclone usually brings precipitation and usually forms clouds.

Section 1 Review

4.) Why do maritime polar air masses have more affect on the west coast than the east coast?

Maritime polar air masses has more affect on the west coast than the east coast because,

of the cool humid air.