Download Weather Notes What is an air mass?

Weather
Notes
What is an air mass?
An air mass is a huge body of air with
uniform temperature, pressure, and
humidity (moisture).
There are four types of air masses
which combine to create the different
climates of the United States.
Tropical: warm air coming from the
tropics, with low pressure.
Polar: cold air coming from the poles,
with high pressure.
Maritime: moist, humid air coming
from over the ocean.
Continental: dry air coming from
inland regions.
See how the different combinations of
air masses give areas their typical
weather type?
Maritime Tropical air masses are
what makes the South so warm and
humid!
Maritime Polar air masses are what
makes Seattle so cold and rainy!
Continental Tropical air masses are
what makes the Southwest so hot and
dry!
Continental Polar air masses are what
make the northern states and Canada
so bitterly cold!
In America, the Prevailing Westerlies
keep 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 masses
run into each other?
Where two air masses collide is called
a FRONT. (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 air
masses and their speed. The faster
moving air mass always wins the front!
Cold Front: fast moving cold air mass
meets slow moving warm air mass.
The warm air gets pushed up out of the
way, 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 air
mass meets slow moving cold air mass.
The faster moving warm air pushes
the cold out of the way!
Warm fronts can bring storms, but they
are slow forming and stay longer.
After the warm front passes,
it is warmer and humid out.
Stationary Front
Front: Both cold and warm
air masses are moving slowly.
Neither air mass is moving fast enough
to push the other out of the way.
The result is that the front gets stalled
and brings many days of rain, fog,
clouds, or snow.
Occluded Front: When a warm air
mass gets caught between two cold
air 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, the
more weight is pushing on your head!
This also means that the higher your
altitude, the less oxygen there will be
to breathe!
(This is why people take oxygen tanks
when climbing Mt. Everest)
#2 = Temperature: When it is cold, the
oxygen will huddle together, putting
even more molecules on your head!
Cold
High Pressure
Hot
Low Pressure
So... why do our ears and bags of chips
pop when going up a hill?
It is because we are used to getting
pushed 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 we
go up a hill and the air isn’t pushing as
much...
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.
To equalize the amount of pressure,
oxygen will move to evenly distribute it.
High Pressure (cold)
Low Pressure (warm)
We can see and feel the oxygen moving...
Air moving from an area of high
pressure to an area of low pressure
is WIND!
With temperature, pressure, and wind
comes all sorts of crazy weather....
floods
hurricanes
thunderstorms
tornado
winter storms