Weather is the condition of the atmosphere at a
certain time and place. The troposphere is where
our weather takes place.

Climate is the average weather conditions in an
area over a long period of time.

The source of all energy in
our atmosphere that fuels
Earth’s weather systems is
the sun.
Radiation – the heat energy that comes from
the sun.
Not all radiation reaches Earth’s surface.
 Some energy is absorbed by the atmosphere.
 Some energy is reflected back into space.
 Most energy is absorbed by the Earth’s surface.
Radiation balance – when the amount of energy
received from the sun equals the amount of energy
returned to space
a. The main reason for unequal heating is the
Earth is curved, so not all areas receive the
same amount of radiation. The sun’s rays
strike Earth most directly at the equator, but
at an angle as you go north or south.
Therefore the equator is warmer than the
poles.
Globe with Flashlight Demo.
1. Hold the flashlight a few inches from the
globe aiming directly at the equator.
2. Hold the flashlight a few inches from the
globe aiming at the poles.
*How does this show that the Poles will
always be cooler than the Equator?
b. Another reason for unequal heating is that
land heats and cools faster than water because
land absorbs the radiation from the sun faster
than water.
Land/Water Demo.
Only the surface of land absorbs heat (through
conduction). This is faster. Water absorbs heat
throughout (through convection). This takes
much longer.
There is a column of air
above you at all times.
The measure of the force
with which air molecules
push on a surface is
air pressure, also
called atmospheric
pressure.
https://www.youtube.com/watch?v=Bv_tS6qCJ4
B. There are 4 factors that influence the air
pressure in an area:
1.
2.
3.
4.
Elevation
Temperature
Water Vapor
Location
Air at sea level has more molecules in each
cubic meter of space than air at the top of a
mountain. The density of air decreases as
altitude increases. Atmospheric pressure is
greatest near Earth’s surface and decreases as
you move upward away from sea level.
Have you ever felt your
ears “pop”?
People are not built for
sudden air pressure
changes.
As people go up, the
outside pressure
decreases. As people
move down, the
outside pressure
increases.
The colder the air, the more the molecules
move toward one another. Colder air is more
dense. More dense air pushes down and has a
higher air pressure than warm air. The warmer
the air, the more the molecules move apart.
Warmer air is less dense. Less dense air rises
upward and has lower air pressure than colder
air.
More water vapor in air has less air pressure
because part of the space is being taken up by
water; therefore there are fewer air molecules
per cubic meter of space available to push
down. The most important function of the
ocean is giving off water vapor into the
atmosphere.
Air closer to the poles is colder and more dense than
air near the equator. Therefore there is more
pressure near the poles than at the
equator. Places that have similar latitudes (distance
from equator) most likely have similar climates. Air
moves in large, circular patterns called convection
cells.


https://www.youtube.com/watch?v=I0C4QR0
OEH0
https://www.youtube.com/watch?v=EkDhlzA
-lwI
A. Differences in air pressure cause wind.
Winds occur because air tends to move from
regions of higher air pressure to regions of
lower air pressure.
Remember the seven dwarfs?
“Hi-Low, Hi-Low, that’s how the wind blows!”
1. As warm air becomes
less dense it rises.
(low pressure)
2. The colder, more dense
air pushes down
(high pressure)
and rushes in to take
the rising, warm air’s place.
3. Winds are named from where they started
or came from.
What winds are
prevailing over the
United States?
Local winds are temporary winds that blow in an
area and are produced by temperature differences
caused by local geographical features.
Ex: Sea and Land breezes
a. Land heats up during the day
b. Air over land gets warmer than air over water
c. warm air over land rises, while cooler,
more dense air from over water
rushes in to take its place
a. Land cools down at night
b. Air over land gets cooler than air over
water
c. Warmer air over ocean rises while
cooler, more dense air from over land
rushes in to take its place (Example:
Before sunrise on the beach, air over
water is warmer than air over land.)
Observe an animation of land and sea breezes.
A. Global winds blow almost constantly in every
direction.
1. Air above the poles is very cold (higher density and
higher pressure).
2. Air above the equator is warmer (less density and
lower pressure).
3. The lower pressure warm air rises and the higher
pressure cold air sinks and rushes toward the lower
pressure areas (equator).
4. The rising, low pressure air at the equator is pushed
toward the poles creating global winds.
http://www.mhhe.com/biosci/genbio/tlw3/eBridge/Chp29/animations/ch29/
global_wind_circulation.swf
Observe an animation of the Coriolis effect
over Earth's surface.
://www.nasa.gov/mov/142348main_coriolisef
fect_hi.mov
D. Jet stream - fast moving, narrow belt of wind that
has a great impact on changing weather conditions
because it determines major air movements.
Air mass - large body of air that gets its temperature and
humidity from the land or water over which it forms
The cause of changes in the weather is when air masses move
and meet.