Transcript Unequal Heating, Air Pressure and Winds

Air has mass.
 Air takes up space.
 Air has density.
 Air pressure is the
weight of a column
of air pressing
down on an area.

Atmosphere held in place by gravity
 Pressure strongest at surface-more air
above you
 *as altitude increases, air pressure
decreases

› Stack of books
As Air Pressure
decreases, so does
density.

Atmosphere: a mixture of gases that
surrounds Earth: acts like a blanket
› Contains oxygen
› Protects from sun
Troposphere: all weather happens here
 Stratosphere: ozone layer-protects us
 Mesosphere: middle layer
 Thermosphere: hottest layer

Nitrogen=78%
 Oxygen=21%
 Other 1%=water vapor, CO2 and other

Sun’s energy travels to earth as
Electromagnetic waves.
 What type of heat transfer is this?

Scattering: Reflections of light in all
directions.
 Why is the sky blue?

Ever feel the heat of the sun on your
face or the heat from standing by a
campfire? That is radiation.
 It is the direct transfer of energy by
electromagnetic waves through space.

Have you walked barefoot on the sand
at the beach and the sand burned your
feet? That is conduction.
 It is the direct transfer of heat from one
substance to another through direct
contact.

Did you come in after
the snow with wet shoes
on and your mother told
you to put them over the
heating vent to dry?
How does this dry them
even though the actual
furnace is in the attic?
That is convection.
 The transfer of heat by
the movement of fluid or
air. Hot air rises, cold air
sinks.

Light/heat from the sun RADIATES
through the atmosphere, hits the Earth
where it is absorbed.
 This heats the air above it by
CONDUCTION.
 This heat rises up to the greenhouse
gases where it is trapped, cools, sinks
and heats at the surface again.CONVECTION.

These gases absorb
the heat and act
as a “blanket” to
keep Earth warm.
 Some greenhouse
gases: water,
methane, carbon
dioxide.

Sun
 Gases
 Sun’s Rays

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 due to
conduction, heat energy is released into the atmosphere,
forming a “bubble” of air which is warmer than the
surrounding air. This “bubble” of air rises into the
atmosphere. As it rises, the air in the “bubble” cools and
becomes more dense. The movement of the air creates
wind. Convection currents are responsible for many
weather patterns in the troposphere.
Convectio
n
Currents!
Differences in air pressure
 More of a difference in pressure = faster winds

Lots of
difference

You know…
› Warm air rises = less dense
› Cool air sinks = more dense
 Now
understand…
› Warm air = less dense
= low pressure
› Cool air = more dense
= high pressure

Created by unequal heating of Earth’s
surface.
 The
movement of
air between the
equator and the
poles produces
global winds.

Coriolis effect
produces patterns of
air circulation called
global winds.
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.
 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 heats up faster than water. Hot air over
land rises (Low Pressure), cool air over water
falls (High Pressure). Winds move from the
water (High Pressure) to the land (Low
Pressure).
Land cools off faster than water. Cool air over
land falls (High Pressure), warm air over water
rises (Low Pressure). Winds move from the land
(High Pressure) to the water (Low Pressure).
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!
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.