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Air and the Sun
 For the most part, the Sun’s energy never actually reaches
the Earth but is lost in space.
 The greenhouse effect is
when the atmosphere traps
heat like the glass of a
greenhouse. If we did not have
a greenhouse effect, the Earth
would reflect back most of the
energy back into space and the
Earth would be very cold and
could not support life.
Air masses form in
large clumps
and move over the
Earth’s surface
slowly
change.
and
Two Properties of air
masses are:
1. Moisture content
2. Temperature
An air mass has some of the
same general
properties as the land
or water that it forms over.
Air masses with moisture form
over water and dry air masses
form over land. Air masses that
form at the poles are cold and
the ones that form in the
tropics (or near the equator)
are warm.
Large Air
Masses
•Huge volumes of air that can cover entire continents or oceans
•Several types and each has specific characteristics
Air mass classification involves two letters.
The first letter describes its moisture properties:
c for continental air masses (dry)
m for maritime air masses (moist)
The second letter describes the thermal characteristic of its source
region:
T for Tropical
P for Polar
A for Arctic or Antarctic
M for Monsoon
E for Equatorial
cP
cT
mP
mT
continental polar
continental tropical
maritime polar
maritime tropical
cold, dry, stable
hot, dry, stable air aloft, unstable surface air
cool, moist and unstable
warm, moist usually unstable
•Clouds are indicators of weather
•For clouds to form, air must be lifted
•Three types of lifting cause clouds.
Convectional
Orographic
Frontal
Orographic lift occurs
when an air mass is
forced from a low
elevation to a higher
elevation as it moves
over rising terrain. As
the air mass gains
altitude it quickly
cools down, which can
raise the humidity to
100% and create
clouds and, under the
right conditions,
precipitation.
Orographic Lifting
Convectional
Lifting
Earth’s surface is
heated by the sun,
which heats the
air mass above it.
The heated air
will then rise.
Cool air sinks.
Frontal
Lifting
One air mass
(warm) is pushed
upward by the other
(cold).
What are
Fronts?
When 2 air masses meet, they do not mix. What
happens is that they form a border that is known as a
front. Most of the weather that we think of happens
along fronts.
Cold Fronts
 A cold front forms when a cold air mass
catches up to a warm air mass.
 Colder air forces the warm air higher
into the atmosphere.
 The warm air that is pushed up cools and
forms clouds. This reaction causes rain
and thunderstorms to occur along a cold
front.
A warm front is when a warm air mass catches up
to a cold air mass. ( Just the opposite of a cold
front.)
Warm air slides over the cold, dense air. This also
causes clouds to form, but many miles ahead of
the front. As the front approaches and passes it
can cause steady rain or snow to fall. After all of
this happens, the sky becomes clear and this is also
when the temperature starts to rise.
A front that stops moving is called a
stationary front. This type of front can
stay in the same place for days.
When this front stays in the same place
for a long time there is constant snow or
rainfall and this leads to several inches of
snow or it could even cause a flood.
1. What is the greenhouse effect?
2. What is an air mass?
3. Give me 3 types of fronts.