Important Vocabulary
Weather – the condition of Earth’s atmosphere
at a particular time and place.
Atmosphere – the envelope of gases that
surrounds the planet
The Main gases in the
Earth’s Atmosphere
• ~ 75% Nitrogen
• 21% Oxygen
• Less than 1% Carbon Dioxide
• Argon makes up most of the
other 1%
Atmosphere
• The atmosphere is a system that interacts with
other Earth systems.
• Events in one part of the atmosphere affect
other parts of the atmosphere.
Air Pressure
• Because air has mass, it also has other
properties, including density and pressure.
Density – the amount of mass in a given volume
of air
D = M/V
Air Pressure – the result of the weight of a column
of pushing on an area
P = F/A
Instruments to measure air pressure
• Barometers
– Mercury barometer
• Consists of a long glass tube that is closed at one end
and open at another
– Aneroid barometer
• Aneroid means “without liquid”
• Has an air tight chamber
• Chamber is connected to a dial by a series of springs
and levers.
• When pressure increases, the thin walls of the chamber
are pushed in. When the pressure drops, the walls
bulge out.
Units of air pressure
• Most weather reports for the public use
inches of mercury. (Ex. The air pressure is 30 inches)
• The National Weather Service maps indicate
air pressure in millibars.
• The pressure of the
atmosphere is equal to
1 bar (1000 millibars).
• 1 inch of mercury =
33.86 millibars
• 30 inches of mercury =
~ 1,016 millibars
• Standard air pressure at sea level is 29.92 inches of
mercury. A mercury reading higher than 30.20
inches, with rising or steady pressure generally
indicates fair weather, becoming cloudy and warmer
with rapidly falling pressure. A mercury reading from
29.80 inches to 30.20 inches with rapidly falling
pressure means precipitation is coming. A mercury
reading under 29.80 inches with rising or steady
pressure means it will start to clear and become
cooler, with slowly falling pressure it is an indication
of precipitation, and rapidly falling pressure would
indicate a storm.
Plickers ?
This barometer uses air tight chamber WITHOUT
liquid to measure air pressure.
A.) Mercury Barometer
B.) Annathermometer
C.) Aneroid Barometer
D.) All barometers
Plickers ?
Most of the atmosphere is made up of ____.
A.) Oxygen
B.) Carbon Dioxide
C.) Argon
D.) Nitrogen
Altitude
• A.K.A elevation, which is the distance above
sea level
• Sea level – average level of the oceans.
• Indiana is about 700 feet above sea level.
• Air pressure decreases as altitude increases.
• Analogy - Stack of books
• As air pressure decreases, so does density.
Altitude continued…
As you go up through the atmosphere, the density
of the air decreases.
Density = mass / volume
– Air contains 21% oxygen, whether you are at sea
level or on top of a mountain, but since there is more
space(volume) at the top of a mountain, the density
decreases.
– Therefore, the air you breathe at the top of a
mountain has fewer oxygen molecules per cubic
meter than at sea level
Plickers ?
Where is the atmospheric pressure the greatest?
A.) closest to earth
B.) in the middle of the atmosphere
C.) at a high altitude
D.) closest to space
Layers of the atmosphere
• Scientists have divided Earth’s
atmosphere in to main layers, which are
classified by changes in temperature.
–Troposphere
–Stratosphere
–Mesosphere
–Thermosphere
Question
• Where is most of the gas in the atmosphere
found?
• Close to Earth’s surface
Troposphere
•
•
•
•
•
•
•
•
•
Where we live
Inner, or lowest layer of Earth’s atmosphere
Tropo – means turning or changing
Weather takes place in this layer
Average thickness is ~ 12 km
Shallowest and most dense layer
Contains almost all the mass of the atmosphere
Altitude goes , temperature goes
Water at the top of this layer forms thin, feathery
clouds of ice
Stratosphere
•
•
•
•
•
Above troposphere
12km – 50 km above Earth’s surface
Strato – means layer or spread out
Contains ozone (O3)
The ozone layer filters out UV light and
absorbs energy from the sun, which warms
the air in this layer
Ozone over time
Mesosphere
• Meso – means middle
• 50 – 80 km above the Earth’s surface
• Protects Earth’s surface from being hit by most
meteroids
Thermosphere
• Outermost layer
• 80 km above Earth’s surface outward into
space
• No definite outer limit
• 2 layers
aurora borealis
– Ionosphere
– exosphere
Plickers ?
What layer of the atmosphere do we live in?
A.) Troposphere
B.) Stratosphere
C.) Mesosphere
D.) Thermosphere
Plickers ?
Which layer means middle layer?
A.) Troposphere
B.) Stratosphere
C.) Mesosphere
D.) Thermosphere
Plickers ?
Which layer of the atmosphere does weather
occur in?
A.) Troposphere
B.) Stratosphere
C.) Mesosphere
D.) Thermosphere
Energy in Earth’s Atmosphere
• Electromagnetic waves – form of energy that
can move through the vacuum of space
• Most of the energy from the sun travels to
Earth in the form of visible light and infrared
radiation. A smaller amount arrives as
ultraviolet radiation.
Visible Light
• Only part of the spectrum we can see
• ROY G BIV
Red
Orange
Green
Blue
Indigo
Violet
• Radiation – the direct transfer of energy by
electromagnetic waves
• Infrared radiation is not visible by humans, but
can be felt as heat.
• The sun gives off ultraviolet radiation.
• Ultraviolet radiation can cause sunburns.
Some sunlight is absorbed or reflected
by the atmosphere before it can reach
the surface. The rest passes through
the atmosphere to the surface.
Scattering – dispersing light in all
direction
Why is the sky blue?
• When you look at the sky, the light you see
has been scattered by gas molecules in the
atmosphere.
• Gas molecules scatter short wavelengths of
visible light (B + V) more than long
wavelengths (R + O)
• Scattered light looks bluer than ordinary
sunlight.
• That’s why the clear daytime sky looks blue.
Greenhouse effect
• Earth’s surface radiates some energy back
into the atmosphere as infrared radiation.
• Much of the IR radiation doesn’t
immediately travel all the way back into
space.
• Instead, it is absorbed and held by water
vapor, CO2, methane, and other gases in
the air.
• The greenhouse effect is a natural process. It
keeps Earth’s atmosphere at a comfortable
temperature.
• Over time, the amount of energy absorbed by
the atmosphere and Earth’s surface is in
balance with the amount of energy radiated
into space.
• In this way, Earth’s average temperatures
remain fairly constant.
Winds
• Differences in air pressure cause the air to
move.
• Wind - the movement of air parallel to Earth’s
surface.
• Most differences in air pressure are caused by
the unequal heating of the atmosphere.
Measuring wind
• Wind direction is determined by a weather vane.
• Anemometer – measures wind speed
• Windchill Factor – the increased cooling that a
wind can cause
– The temp outside is 20 °F, but with a wind speed of
30 mph, the windchill factor makes it feel like 1 °F
Local Winds
• Winds that blow over short
distances are called local
winds.
• Local winds are caused by
the unequal heating of
Earth’s surface within a small
area.
• These winds form only when
large scale winds are weak.
• 2 types of local winds
– Sea breezes
– Land breezes
Local vs. Global
• Like local winds, global winds are created by
the unequal heating of the Earth’s surface.
• Unlike local winds, global winds occur over a
large area.
Global winds and the jet stream have an effect on weather
and climatic conditions on Earth.
•Global winds are found in
each convection region.
•Because convection cells are
in place in the atmosphere
and Earth is spinning on its
axis, these global winds
appear to curve. This is
known as the Coriolis effect.
MENU
•In the global wind belt
regions, the prevailing
direction of the winds and
how air movement in these
large regions affects weather
conditions.
•The trade winds blow from
east to west in the tropical
region moving warm tropical
air in that climate zone.
Doldrums – calm
area where warm
air rises
Horse latitudes –
2 calm areas of
sinking air
Trade winds blow
from the horse
latitudes toward
the equator
Prevailing westerlies blow from west to east
Polar easterlies blow cold air away from the poles
•The prevailing westerly winds blow
from west to east in the temperate
region.
•The temperate zone temperatures are
affected most by the changing seasons,
but since the westerly wind belt is in
that region, the weather systems during
any season move from west to east.
Since the United States is in the
westerly wind belt, the weather systems
move across the country from west to
east.
•Convection can cause
global winds. These winds
then move weather
systems and surface ocean
currents in particular
directions.
•Due to the spinning of
Earth, the weather systems
in these regions move in
certain directions because
the global wind belts are
set up.
Invention of weather instruments
1500’s Galileo invented water thermometer
1643 Torricelli invented mercury barometer
1667 Hooke invented anemometer
1719 Fahrenheit developed temp scale based on
boiling/freezing water
1735 Hadley explained how the earth’s rotation influences
winds in tropics
1742 Celsius developed the centigrade temp scale
• 1787 Charles discovered relationship
between temp and a volume of air
• 1835 Coriolis used math to demonstrate the
effect that the earth’s rotation has on atmos.
Motions
• 1869 first isobars were placed on map
• 1920 concepts of air masses and weather
fronts were formulated in Norway
• 1940’s upper air ballons/3-D view of atmos
• 1950’s high speed computers
• 1960 Tiros 1 first weather satellite