Download 8_ch16 - Clinton Public Schools

The Atmosphere
&
Weather
Bell Work
•What is the most abundant gas in
the atmosphere?
• Weather
• Condition of Earth’s
atmosphere at a
particular time and
place
• Atmosphere
• The envelope of gases
that surrounds the
planet
Composition of Earth’s Atmosphere:
• 1. Nitrogen –most abundant; ¾ of the air we breathe
• 2. Oxygen – 2nd most abundant, usually molecules have 2
oxygen atoms
• Ozone – form of oxygen with 3 oxygen atoms per molecule
- forms when lightning interacts with oxygen in air
(odor after thunderstorm)
3. Carbon Dioxide- increased when fuels (coal & gas) burn
4. Other Gases – “trace gases”  only small amounts
present
• Water Vapor
• Water in the form of a gas
• Invisible
• NOT the same as steam (tiny drops of liquid water
• Plays an important role in EARTH’s WEATHER
• Water Vapor condenses  clouds form  clouds contain
tiny droplets of liquid water(rain) OR crystals of
ice(snow/sleet)
• If the droplets/crystals become heavy enough they fall to
the Earth.
Why is the Atmosphere
Important?
• Makes conditions of Earth suitable for living.
• Contains oxygen living things need
• Traps energy from the sun
• Living things need warmth
• Keeps Earth’s surface warm enough for water to
exist as a liquid
• Protects living things from the sun’s radiation
• Prevents Earth’s surface from being hit by most
meteoroids
Air Pressure
• Does Air have Mass?
• If it has mass, it has to contain other properties!
• Properties of Air:
• 1. Density = Mass/Volume
• Air's density depends on:
• Its temperature
• Its pressure
• Amount of water vapor
Air Pressure
• Properties of Air:
• 2. Pressure – force pushing on an area or surface
• The ATMOSPHERE’s weight puts a force on surfaces
• Air Pressure – result of the weight of a column of air pushing
down on an area
• Atmosphere is heavy, but doesn’t crush us because the molecules
push in all directions
• On objects/People - Air pushing DOWN is balanced by air pushing UP
• Air pressure changes daily:
• Dense object  more mass per volume
• Dense air  exerts MORE pressure than less dense air
Measuring Air Pressure
• Barometer – an instrument used to
measure air pressure
• Two types of Barometers:
• 1. Mercury Barometer
• Consists of a glass tube open at the
bottom end and partially filled with
mercury
• Space at top of tube is vacuum (very
little air)
• Air pressure on the dish of mercury
= pressure of weight of column of
mercury in tube
• Air pressure increases presses on
mercury more  vacuum decreases
Measuring Air
Pressure
• 2. Aneroid Barometer
• Air tight metal chamber that is
sensitive to changes in air
pressure
• Air pressure increases  walls
are pushed in
• Air pressure decreases walls
bulge out
• As the shape changes the
needle on the dial moves
Altitude &
the Properties of Air
• Altitude – distance above sea level
• Altitude Affect Air Pressure
• Air pressure decreases as Altitude Increases
• Sea level(greatest) vs Mountain Top(Least)
• Why?
• Altitude Affects Density
• Density decreases as Altitude Increases
• Gas molecules in the atmosphere are father apart at HIGH altitudes
than they are at sea level
• Is it harder to breathe at sea level or on top of a mountain?
• Why?
Layers of the
Atmosphere
• Classified according to
changes in temperature
• Four Main Layers
•
•
•
•
1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere
The Troposphere
• Lowest Layer/Layer we live in
• LAYER IN WHICH EARTH’s
WEATHER OCCURS
• 16 km above equator & less than
9 km above poles
• Most of the mass of the
atmosphere
• Altitude Increases 
Temperature Decreases
(opposite of stratosphere)
The
Stratosphere
• From top of troposphere to about 50
km above Earth
• Second Layer of Atmosphere
• Contains the OZONE LAYER
• Protects Earth’s living things fro UV
radiation from the sun
• Altitude Increases  Temperature
Increases (opposite of Troposphere)
• Middle contains a layer of air with
more ozone
• Ozone absorbs energy from the sun to
create heat
The
Mesosphere
• Above the stratosphere,
marked by a drop in
temperature
• “meso”- middle layer of
atmsophere
• 50km above Earth – 80 km
above Earth
• Protects Earth’s surface from
being hit by most
meteoroids
The Thermosphere
• Outermost layer of Earth’s
Atmosphere
• 2 Layers
• 1. Ionosphere
• Extends from 80 km above Earth and
gradually blends into space
• Very thin, hot air
• sunlight strikes the thermosphere
first
• The lower layer
• 80 km above the surface and
extends to about 400 km.
• Gas molecules here are electrically
charged because of the sun's
energy.
• Radio waves bounce back from
the ionosphere to Earth’s surface
• Location of Auroras
• 2. Exosphere
• The outer layer