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8-3: Air Masses and Fronts 6 th Grade Earth Science

8-3: Air Masses and Fronts · 8-3: Air Masses and Fronts Summary •Large air masses form on earth. •When they collide, a front forms. •Fronts can bend and start rotating,

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8-3: Air Masses and Fronts

6th Grade Earth Science

8-3: Air Masses and Fronts

• An air mass is a huge body of air that has similar temperature, humidity, and air pressure, up to 10 km deep.

Air Mass

8-3: Air Masses and Fronts

• There are four major types of air masses that influence the USA.

1. Tropical

2. Polar

3. Maritime

4. Continental

Types of Air Masses

8-3: Air Masses and Fronts

• Tropical air masses form in the tropics and have low pressure.

Tropical Air Masses

8-3: Air Masses and Fronts

• Polar air masses form above 50 degrees latitude (north or south).

• They are cold and have high pressure.

Polar Air Masses

8-3: Air Masses and Fronts

• If the air mass formed over water, it is called maritime – and it is humid (no surprise right?)

• If it formed over land it is called continental – and it is dry – makes sense.

Moist or Dry?

8-3: Air Masses and Fronts

8-3: Air Masses and Fronts

Maritime Tropical

8-3: Air Masses and Fronts

• Maritime tropical air is warm and moist.

• They move north into the southern USA and the west coast.

Maritime Tropical

8-3: Air Masses and Fronts

Maritime Polar

8-3: Air Masses and Fronts

• Maritime polar air is cold and humid.

• Brings fog and cool temperatures to the west coast of the USA.

Maritime Polar

8-3: Air Masses and Fronts

Continental Tropical

8-3: Air Masses and Fronts

• Continental Tropical air is hot and dry!!

• They move northeast from Mexico bringing hot, dry weather to the Great Plains.

Continental Tropical

8-3: Air Masses and Fronts

Continental Polar

8-3: Air Masses and Fronts

• Continental polar air is cold and dry.

• They move south from Canada into the USA and collide with maritime tropical air, producing storms.

Continental Polar

8-3: Air Masses and Fronts

• Air masses move as they are pushed around by prevailing westerlies and the jet stream, from west to east.

How Air Masses Move

8-3: Air Masses and Fronts

• Where two different air masses collide, a front forms, where weather is changing.

• For kinds exist:

1. cold fronts

2. warm fronts

3. stationary fronts

4. occluded fronts.

Fronts

8-3: Air Masses and Fronts

• When a cold air mass is moving into a warm air mass, a cold front forms.

• Cold air pushes warm air up, causing clouds and heavy rain.

Cold Fronts

8-3: Air Masses and Fronts

• When a warm air mass is moving into a cold air mass, a warm front forms.

• Warm air rises up over the cold air, causing cirrus and stratus which can produce a gentle rain.

Warm Fronts

8-3: Air Masses and Fronts

• When a warm and cold air mass are next to each other, but not moving, it is called a stationary front.

• If the warm air is humid, condensation can form and a gentle rain may fall.

Stationary Front

8-3: Air Masses and Fronts

Occluded Front

8-3: Air Masses and Fronts

• When a cold air mass catches up to another cold air mass, the warm air gets trapped and pushed up, creating an occluded front.

• This sometimes creates some of the most violent thunderstorms.

Occluded Front

8-3: Air Masses and Fronts

8-3: Air Masses and Fronts

Cyclones / Anticyclones

8-3: Air Masses and Fronts

Cyclones / Anticyclones

• When a front starts to bend, the air can start to rotate counter clockwise around a developing low pressure – called a cyclone.

• Air rises and cools and rain can develop.

8-3: Air Masses and Fronts

• Anticyclones are the opposite of a cyclone, high pressure causes air to spiral outward clockwise.

• Air is sinking, warming, and drying. So high pressures are associated with fair weather.

8-3: Air Masses and Fronts

• In the southern hemisphere, lows and highs rotate opposite of what they do in the northern hemisphere.

• Global Video Link

• Cyclone in northern hemisphere.

8-3: Air Masses and Fronts Summary

• Large air masses form on earth.

• When they collide, a front forms.

• Fronts can bend and start rotating, creating a low pressure cyclone.

• Other areas with too much air pressure rotate counter clockwise as air flows toward the low pressures.