Air Masses, Fronts, Global Winds, and MoreAir Masses, Fronts, Global Winds, and More

byby

Mr. WoodhamMr. Woodham

for myfor my

66thth Grade Earth Science Class Grade Earth Science Class

• Differences in air pressureDifferences in air pressure are caused by are caused by unequal heatingunequal heating of Earth’s of Earth’s surface. (Why does Earth heat unequally?)surface. (Why does Earth heat unequally?)

• The region along the The region along the equator receives more solar energyequator receives more solar energy than the regions than the regions at the poles do so at the poles do so air rises at the equator creating low pressure centersair rises at the equator creating low pressure centers..

• Conversely, Conversely, cold air near the pole sinks and creates high-pressure cold air near the pole sinks and creates high-pressure centerscenters..

• Differences in air pressureDifferences in air pressure at different locations on Earth at different locations on Earth create wind create wind patternspatterns..

How Air MovesHow Air Moves

How Air MovesHow Air Moves• Air moves from areas of high pressure to areas of low pressure. Air moves from areas of high pressure to areas of low pressure.

Therefore, there is a general, worldwide movement of surface air Therefore, there is a general, worldwide movement of surface air from the poles toward the equator.from the poles toward the equator.

• Temperature and pressure differences on Earth’s surface create Temperature and pressure differences on Earth’s surface create three wind belts in the Northern Hemisphere and three wind belts in three wind belts in the Northern Hemisphere and three wind belts in the Southern Hemisphere.the Southern Hemisphere.

• The Coriolis effect, which occurs when The Coriolis effect, which occurs when winds are curved clockwise winds are curved clockwise in the Northern Hemispherein the Northern Hemisphere by Earth’s rotationby Earth’s rotation, also influences wind , also influences wind patternspatterns..

Earth’s Climate ZonesEarth’s Climate Zones• Weather is the condition of Earth’s atmosphere at a particular time Weather is the condition of Earth’s atmosphere at a particular time

and placeand place• Climate is the average, year-after-year conditions of temperature, Climate is the average, year-after-year conditions of temperature,

precipitation, winds, and clouds in an area.precipitation, winds, and clouds in an area.

Air in the Tropical Zone is generally warm and moist.Air in the Tropical Zone is generally warm and moist.

Global WindsGlobal Winds• The global winds that affect the U.S. are the The global winds that affect the U.S. are the prevailing westerliesprevailing westerlies..• This means the wind is coming from the west most of the time.This means the wind is coming from the west most of the time.• These westerlies are responsible for moving weather from west to These westerlies are responsible for moving weather from west to

east across the U. S.east across the U. S.• Another global wind is the Another global wind is the jet streamjet stream..• The The jet streamjet stream has a great impact on changing weather conditions has a great impact on changing weather conditions

in an area because it in an area because it is a determinant of major air movementsis a determinant of major air movements..• The jet stream is at the top of the troposphere and is what generally The jet stream is at the top of the troposphere and is what generally

moves weather north and south in the U.S.moves weather north and south in the U.S.

Formation of Air MassesFormation of Air Masses

• air massair mass a large body of air throughout which temperature and a large body of air throughout which temperature and moisture content are similarmoisture content are similar

• When air pressure differences are small, air remains relatively When air pressure differences are small, air remains relatively stationary.stationary.

• If If airair remains stationary or remains stationary or moves slowly over a land or watermoves slowly over a land or water, the , the air air takes on the characteristic temperature and humidity of the land takes on the characteristic temperature and humidity of the land or wateror water..

• Air masses that form over frozen polar regions are very cold and air Air masses that form over frozen polar regions are very cold and air masses that form over tropical regions are warm.masses that form over tropical regions are warm.

• An air mass may remain over its source region for days or weeks. An air mass may remain over its source region for days or weeks. However, However, the air mass will eventually movethe air mass will eventually move into other regions into other regions because of global wind patternsbecause of global wind patterns

Types of Air MassesTypes of Air Masses• There are two types of air masses, There are two types of air masses, continentalcontinental and and maritimemaritime air masses. air masses.

• Air masses that form over the ocean are called Air masses that form over the ocean are called maritimemaritime. Air masses that form . Air masses that form over land are called over land are called continentalcontinental..

• There are two types of continental air masses: There are two types of continental air masses: continental polarcontinental polar and and continental continental tropicaltropical..

• Continental polar air masses form at high latitudes and are cold and dryContinental polar air masses form at high latitudes and are cold and dry.. Continental tropical air masses form at equatorial latitudes and are warm and dry.Continental tropical air masses form at equatorial latitudes and are warm and dry.

• There are two types of maritime air masses: There are two types of maritime air masses: maritime polarmaritime polar and and maritime tropicalmaritime tropical..

• Maritime polar air masses are cold and wet. Maritime polar air masses are cold and wet. Maritime tropical air masses are Maritime tropical air masses are warm and wetwarm and wet..

Types of Air MassesTypes of Air MassesThe diagram below shows the four types of air mass that influence The diagram below shows the four types of air mass that influence

North America.North America.

Weather-Air MassesWeather-Air Masses

The weather in Georgia is influenced most often by maritime tropical air The weather in Georgia is influenced most often by maritime tropical air masses coming up from the Gulf of Mexico.masses coming up from the Gulf of Mexico.

What kind of air can we expect to get with this air mass?What kind of air can we expect to get with this air mass?

Note CheckNote Check

Why does Earth heat unequally?Why does Earth heat unequally?

Is there low or high pressure at the Equator?Is there low or high pressure at the Equator?

What global wind is responsible for moving weather north and south inWhat global wind is responsible for moving weather north and south inthe U.S.?the U.S.?

What kind of air mass is cold and wet?What kind of air mass is cold and wet?

What kind of air mass is warm and dry?What kind of air mass is warm and dry?

What kind of air mass most often affects Georgia?What kind of air mass most often affects Georgia?

FrontsFronts

• The area where The area where air masses of differing temperature and humidity collideair masses of differing temperature and humidity collide are are known as weather known as weather frontsfronts..

• The two types of fronts we are concerned with are The two types of fronts we are concerned with are warm frontswarm fronts and and cold cold frontsfronts..

• As we have learned, As we have learned, cold air is more dense and sinkscold air is more dense and sinks while while warm air is less warm air is less dense and tends to risedense and tends to rise..

When a warm front air mass and a cold front air mass meet, which one is likely When a warm front air mass and a cold front air mass meet, which one is likely to stay closer to the ground?to stay closer to the ground?

Which one is likely to be on top of the other?Which one is likely to be on top of the other?

Weather FrontsWeather Fronts

FrontsFrontsCold FrontCold Front• Cold fronts tend to move fast through an area.Cold fronts tend to move fast through an area.• When a cold frontWhen a cold front overtakes a warm front it dives beneath the warm frontovertakes a warm front it dives beneath the warm front..• Warm air has evaporated a lot of water in the form of the gas, water vapor.Warm air has evaporated a lot of water in the form of the gas, water vapor.• As a warm front is wedged upwardAs a warm front is wedged upward over the cold front, the air it meets in the over the cold front, the air it meets in the

troposphere gets colder and troposphere gets colder and causes the water vapor to condensecauses the water vapor to condense around around dust particles forming clouds of liquid water. dust particles forming clouds of liquid water.

• If enough water vapor condenses, it results in precipitation, if not, it might If enough water vapor condenses, it results in precipitation, if not, it might just be a cloudy day.just be a cloudy day.

• Since Since cold frontscold fronts move quickly, they move quickly, they can cause can cause sudden changes to an area, sudden changes to an area, like like thunderstormsthunderstorms..

FrontsFronts

Warm FrontWarm Front• Sometimes a Sometimes a warm frontwarm front will overtake a slow moving cold front and will overtake a slow moving cold front and

move over the topmove over the top of the cold front. of the cold front.• If the air mass that makes up the warm front is humid, light rain or If the air mass that makes up the warm front is humid, light rain or

snow may fall along the front edge.snow may fall along the front edge.• Since warm fronts generally move slow, it may be rainy or cloudy for Since warm fronts generally move slow, it may be rainy or cloudy for

many days.many days.

Dew and FrostDew and Frost• Whether it is high in the atmosphere or close to the ground, the Whether it is high in the atmosphere or close to the ground, the

temperature at which the gas water vapor condenses into liquid temperature at which the gas water vapor condenses into liquid water is called the dew point.water is called the dew point.

• If the If the dew point is above 0dew point is above 0ºCºC ( (3232ºF), the freezing point of water, the ºF), the freezing point of water, the water vapor forms water droplets called dewwater vapor forms water droplets called dew..

• If the If the dew point is below dew point is below 00ºCºC ( (3232ºF), the ºF), the water vapor may changewater vapor may change directly from a gas to a solid in the form of directly from a gas to a solid in the form of ice called frostice called frost. .

• Dew on the grass is pretty much the same thing as a cloud in the Dew on the grass is pretty much the same thing as a cloud in the sky that will end up producing rain.sky that will end up producing rain.

• Frost on a windshield is pretty much the same thing as a cloud in Frost on a windshield is pretty much the same thing as a cloud in the sky that will produce snow or ice.the sky that will produce snow or ice.

Final Note CheckFinal Note Check

If a warm front overtakes a cold front, what kind of weather would you MOST LIKELYIf a warm front overtakes a cold front, what kind of weather would you MOST LIKELYget?get?

What is the MOST LIKELY weather event if a cold front overtakes a warm front?What is the MOST LIKELY weather event if a cold front overtakes a warm front?

When a cold front and a warm front meet, which one will rise up over the other one?When a cold front and a warm front meet, which one will rise up over the other one?

It is a warm summer night. The relative humidity is 100%. From dusk until dawn, theIt is a warm summer night. The relative humidity is 100%. From dusk until dawn, theair temperature drops from 32air temperature drops from 32ººC to 18C to 18ººC. What would you expect to see in theC. What would you expect to see in themorning? Remember, in Celsius, the freezing point is 0morning? Remember, in Celsius, the freezing point is 0º.º.

It is a cool spring night. The relative humidity is high. From dusk until dawn, the airIt is a cool spring night. The relative humidity is high. From dusk until dawn, the airtemperature drops from 14temperature drops from 14ºC to -1ºC. ºC to -1ºC. What would you expect to see in the morning? What would you expect to see in the morning?

What is happening to the gas, water vapor, when it is changing into clouds or dew?What is happening to the gas, water vapor, when it is changing into clouds or dew?