Transcript cold fronts - woodhamwiki

Air Masses, Fronts, Global Winds, and More
by
Mr. Woodham
for my
6th Grade Earth Science Class
How Air Moves
• Differences in air pressure are caused by unequal heating of Earth’s
surface. (Why does Earth heat unequally?)
• The region along the equator receives more solar energy than the regions
at the poles do so air rises at the equator creating low pressure centers.
• Conversely, cold air near the pole sinks and creates high-pressure
centers.
• Differences in air pressure at different locations on Earth create wind
patterns.
How Air Moves
• Air moves from areas of high pressure to areas of low pressure.
Therefore, there is a general, worldwide movement of surface air
from the poles toward the equator.
• Temperature and pressure differences on Earth’s surface create
three wind belts in the Northern Hemisphere and three wind belts in
the Southern Hemisphere.
• The Coriolis effect, which occurs when winds are curved clockwise
in the Northern Hemisphere by Earth’s rotation, also influences wind
patterns.
Earth’s Climate Zones
• Weather is the condition of Earth’s atmosphere at a particular time
and place
• Climate is the average, year-after-year conditions of temperature,
precipitation, winds, and clouds in an area.
Air in the Tropical Zone is generally warm and moist.
Global Winds
• The global winds that affect the U.S. are the prevailing westerlies.
• This means the wind is coming from the west most of the time.
• These westerlies are responsible for moving weather from west to
east across the U. S.
• Another global wind is the jet stream.
• The jet stream has a great impact on changing weather conditions in
an area because it is a determinant of major air movements.
• The jet stream is at the top of the troposphere and is what generally
moves weather north and south in the U.S.
Formation of Air Masses
• air mass a large body of air throughout which temperature and
moisture content are similar
• When air pressure differences are small, air remains relatively
stationary.
• If air remains stationary or moves slowly over a land or water, the air
takes on the characteristic temperature and humidity of the land or
water.
• Air masses that form over frozen polar regions are very cold and air
masses that form over tropical regions are warm.
• An air mass may remain over its source region for days or weeks.
However, the air mass will eventually move into other regions
because of global wind patterns
Types of Air Masses
• There are two types of air masses, continental and maritime air
masses.
• Air masses that form over the ocean are called maritime. Air masses
that form over land are called continental.
• There are two types of continental air masses: continental polar and
continental tropical.
• Continental 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.
• There are two types of maritime air masses: maritime polar and
maritime tropical.
• Maritime polar air masses are cold and wet. Maritime tropical air
masses are warm and wet.
Types of Air Masses
The diagram below shows the four types of air mass that influence
North America.
Weather-Air Masses
The weather in Georgia is influenced most often by maritime tropical air
masses coming up from the Gulf of Mexico.
What kind of air can we expect to get with this air mass?
Note Check
Why does Earth heat unequally?
Is there low or high pressure at the Equator?
What global wind is responsible for moving weather north and south in
the U.S.?
What kind of air mass is cold and wet?
What kind of air mass is warm and dry?
What kind of air mass most often affects Georgia?
Fronts
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The area where air masses of differing temperature and humidity collide are
known as weather fronts.
The two types of fronts we are concerned with are warm fronts and cold
fronts.
As we have learned, cold air is more dense and sinks while warm air is less
dense and tends to rise.
When a warm front air mass and a cold front air mass meet, which one is likely
to stay closer to the ground?
Which one is likely to be on top of the other?
Weather Fronts
Fronts
Cold Front
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Cold fronts tend to move fast through an area.
When a cold front overtakes 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.
As a warm front is wedged upward over the cold front, the air it meets in the
troposphere gets colder and causes the water vapor to condense around
dust particles forming clouds of liquid water.
If enough water vapor condenses, it results in precipitation, if not, it might
just be a cloudy day.
Since cold fronts move quickly, they can cause sudden changes to an area,
like thunderstorms.
Fronts
Warm Front
• Sometimes a warm front will overtake a slow moving cold front and
move over the top of the cold front.
• If the air mass that makes up the warm front is humid, light rain or
snow may fall along the front edge.
• Since warm fronts generally move slow, it may be rainy or cloudy for
many days.
Dew and Frost
• Whether it is high in the atmosphere or close to the ground, the
temperature at which the gas water vapor condenses into liquid
water is called the dew point.
• If the dew point is above 0ºC (32ºF), the freezing point of water, the
water vapor forms water droplets called dew.
• If the dew point is below 0ºC (32ºF), the water vapor may change
directly from a gas to a solid in the form of ice called frost.
• Dew on the grass is pretty much the same thing as a cloud in the
sky that will end up producing rain.
• Frost on a windshield is pretty much the same thing as a cloud in the
sky that will produce snow or ice.
Final Note Check
If a warm front overtakes a cold front, what kind of weather would you MOST LIKELY
get?
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?
It is a warm summer night. The relative humidity is 100%. From dusk until dawn, the
air temperature drops from 32ºC to 18ºC. What would you expect to see in the
morning? Remember, in Celsius, the freezing point is 0º.
It is a cool spring night. The relative humidity is high. From dusk until dawn, the air
temperature drops from 14ºC to -1ºC. 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?