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WeatherNotes
What is an air mass?
An air mass is a huge body of air withuniform temperature, pressure, and humidity (moisture).
There are four types of air masseswhich combine to create the differentclimates of the United States.
Tropical: warm air coming from thetropics, with low pressure.
Polar:Polar: cold air coming from the poles,with high pressure.
Maritime:Maritime: moist, humid air comingfrom over the ocean.
Continental:Continental: dry air coming from inland regions.
See how the different combinations ofair masses give areas their typicalweather type?
Maritime TropicalMaritime Tropical air masses are what makes the South so warm and humid!
Maritime PolarMaritime Polar air masses are whatmakes Seattle so cold and rainy!
Continental Tropical air masses arewhat makes the Southwest so hot and dry!
Continental PolarContinental Polar air masses are whatmake the northern states and Canadaso bitterly cold!
In America, the Prevailing Westerlieskeep most air masses moving from West to East.
They turn because of the spinning of the Earth. This is called Coriolis Effect.
What happens when two air massesrun into each other?
Where two air masses collide is calleda FRONTFRONT. (like a battle front)
There are four types of fronts, all of which tend to cause clouds and rain.
The type of front depends on the airmasses and their speed. The faster moving air mass always wins the front!
Cold Front: fast moving cold air massmeets slow moving warm air mass.
The warm air gets pushed up out of theway, so the cold air stays underneath.
Cold fronts usually cause sudden weather changes and storms.
After the cold front passes, it is clear and colder out.
Warm Front: fast moving warm airmass meets slow moving cold air mass.
The faster moving warm air pushesthe cold out of the way!
Warm fronts can bring storms, but theyare slow forming and stay longer.
After the warm front passes, it is warmer and humid air.
Stationary FrontStationary Front: Both cold and warmair masses are moving slowly.
Neither air mass is moving fast enoughto push the other out of the way.
The result is that the front gets stalledand brings many days of rain, fog, clouds, or snow.
Occluded Front: When a warm airmass gets caught between two coldair masses.
(Occluded means blocked)
Occluded fronts can bring clouds, rain, and even snow.
The two things that affect the weather the MOST are:
1) Temperature
2) Air Pressure
There are two main factors that decide what air pressure we feel.
#1 = Altitude: how high up in the atmosphere you are.
Oxygen is heavier than Nitrogen, so it sinks to the bottom of the atmosphere.
That means that the lower you are, themore weight is pushing on your head!
This also means that the higher youraltitude, the less oxygen there will beto breathe!
(This is why people take oxygen tankswhen climbing Mt. Everest)
#2 = Temperature: When it is cold, theoxygen will huddle together, puttingeven more molecules on your head!
Cold Hot
High Pressure Low Pressure
So... why do our ears and bags of chipspop when going up a hill?
It is because we are used to gettingpushed on by the pressure of the air.
So that our head doesn’t get crushed,it pushes back against the pressure...
(Remember Newton’s 3rd Law? For every action there is an equal and opposite reaction!)
Unfortunately this means that when wego up a hill and the air isn’t pushing asmuch...
Our head is still pushing back a lot and could explode like the bag of chips!
Luckily, we are able to release the pressure inside our heads by popping our ears!
We let some of the air that is pushing up get free, and the pressure is equalized.
High Pressure (cold) Low Pressure (warm)
To equalize the amount of pressure, oxygen will move to evenly distribute it.
We can see and feel the oxygen moving...
Air moving from an area of high pressure to an area of low pressureis WIND!
With temperature, pressure, and wind comes all sorts of crazy weather....
floods thunderstormswinter storms
hurricanes tornado
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