Transcript Unequal Heating, Air Pressure and Winds1

Review of Atmosphere
Air: has mass, takes up space, has density, held in place by gravity
Air pressure is the weight of a column of air pressing down on an area, but we do
not feel it because it pushes on us everywhere, the force is balanced or equal.
Pressure strongest at surface-more air above you
*as altitude increases, air pressure decreases, density decreases
Higher elevations—air is LESS dense, the molecules of oxygen are “more spread
out” so it is harder to breathe.
Atmosphere:
:a mixture of gases that surrounds Earth
: acts like a blanket to keep us warm
Contains
78% nitrogen
21% oxygen
1% water vapor, CO2 and other gases
Protects from sun’s UV radiation
 Light/heat from the sun RADIATES by
electromagnetic waves through the atmosphere,
hits the Earth where it is absorbed.

This heats the air above it by CONDUCTION,
the direct contact with molecules.
This heat rises up
to the greenhouse
gases where it is
trapped, cools, sinks
and heats at the
surface again.CONVECTION.
Radiation
 Sun on your face
 standing by campfire
 direct transfer of energy by
electromagnetic waves
through space.
Conduction
Bare feet burned by hot
sand
direct transfer of heat from
one substance to another
through direct contact.
Convection
Basement colder than
upstairs
transfer of heat by the
movement of fluid or air.
Hot air rises, cold air sinks.
Greenhouse gases
(water, methane,
carbon dioxide)
absorb the heat
and act as a
“blanket” to keep
Earth warm.
 http://www.youtub
e.com/watch?v=Hi
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
 Air in the atmosphere acts as a
fluid (water vapor).
 The sun's radiation strikes the
ground, warming the rocks/ground.
 As the ground’s temperature rises, air molecules begin
to move faster, “spread out”, and the LESS DENSE
“bubble” of air begins to rise into the atmosphere.
 As it rises, the air in the “bubble” cools and becomes
MORE DENSE.
AIR PRESSURE
as the LESS DENSE, warmer air molecules
rise…less pressure (less air molecules in an area) is
on the surface forming a LOW pressure and a HIGH
pressure above
 MORE DENSE, cooler air molecules sink…HIGH Pressure
WIND
”horizontally” air moves from
HIGH to LOW pressure
**THINK: nature wants
everything equal…analogy
1 full bucket one empty…how do they
become equal? Pour some from the high
bucket to the low bucket
Convection
Currents!
Starts with uneven heating of the Earth's surface by the sun.
 Because the Earth's surface is made of very different types
of land and water, it absorbs the sun's heat at different
rates.
 This causes differences in air pressure
 More of a difference in pressure = faster winds
 Air moves from HIGH to LOW pressure

 Now
understand…
› Warm air = less dense
= low pressure
› Cool air = more dense
= high pressure
Land absorbs and releases the sun's heat at
a FASTER rate then water
 Uneven heating of the Earth's surface causes

differences in air pressure
 Air moves from HIGH to LOW pressure
 WIND blows horizontally
Warm air
less dense
Low pressure
Cool air
more dense
High pressure
Unequal heating of
earth’s surface on a
global scale…think
BIG!
 Movement of air
between the equator
and the poles
 Coriolis effect
produces patterns of
air circulation


Major global wind systems:
 Polar easterlies, Westerlies, and Trade winds.
Doldrums
• Where the trade winds
meet around the
equator
• Very little wind because
the warm air rising = low
pressure
Horse
Latitudes
• High pressure
areas… 300N and
300S
• Very week winds
Bands of high speed winds
 Upper troposphere and
lower stratosphere
 Blow from west to east at
speeds of 200-400 km/hr.
 Reason why weather
systems move from west
 Help airplanes save fuel
and time when traveling
east.

Have you ever flown a kite at the beach on a
hot summer day? Even if there is no wind
inland, there may be a cool breeze
blowing in from the water toward the
beach. This breeze is an example of local
winds!
Local winds are winds that
blow over short distances.
 They are caused by unequal
heating of Earth’s surface
within a small area.
 Types:

› sea breezes and land breezes
› Mountain breeze and valley
breeze
LAND gains heat (warms up) and loses heat (cools down) FASTER than water.
 Hot air over land rises
(Low Pressure), cooler
air over water falls (High
Pressure).
 Cooler air over land sinks
(High Pressure), warm air
over water rises (Low
Pressure).
 Winds move from the
water (High Pressure) to
the land (Low Pressure).
 Winds move from the land
(High Pressure) to the
water (Low Pressure).
Wind Vane




Winds are described by their
direction and speed.
Wind direction is determined
with a wind vane – points in the
direction the wind is moving!
Wind speed is measured with an
anemometer.
The increased cooling that a
wind can cause is called the
wind chill factor.
Anemometer – The cups
catch the wind, turning
faster when the wind
blows faster.
During the day the sun warms the air slopes,
creating a valley breeze…
at nightfall, the air along the mountain slopes
cools…
This cool air moves down the slopes into the
valley, producing a mountain breeze!