Download Atmosphere - TeacherWeb

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Atmosphere
* The atmosphere is a thin layer of gases that
surrounds the Earth.
* Often the word “air” is used to describe this
layer of gases- but there is so much more to it
than that.
* Composed of several layers.
*
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Atmospheric Component
Percent by Volume
(%/vol)
Nitrogen (N)
Oxygen (O₂)
78.08
21
Argon (Ar)
Water Vapor (H₂O)
0.9
Carbon Dioxide (CO₂)
0.036
Methane (CH₄)
0.00017
Nitrous Oxide (NO)
0.00003
Ozone (O₃)
0.000004
Particles (dust, soot, etc)
0.000001
0.4
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Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere
* The lowest layer Earth’s atmosphere.
* Most of the Earth’s weather occurs in the
Troposphere
* Tropo- means “turning” or “changing”.
* Depth varies from more than 16 km above the
equator to less than 9 km above the North and
South Poles.
* Contains almost all of the mass of the
atmosphere.
* As altitude increases in the troposphere, the
temperature decreases.
*
* UV light and other forms of energy from the
Sun are absorbed or reflected by water and
land
* The heat is transferred to the air directly
above the land or water by conduction and
radiation
*
* Extends from the top of the troposphere to about
50 km above Earth’s surface.
* Strato- means “layer” or “spreading out”.
* Lower stratosphere is cold, about -60°C.
* The upper stratosphere is warmer than the lower
stratosphere.
* Upper Stratosphere contains ozone (O₃)in the
stratosphere absorbs energy from the sun,
converting it into heat, and warming the air.
* Most Clouds are located in the Stratosphere
*
* Located above the stratosphere
* Cooler than the stratosphere
* Meso- mean s “middle”.
* Begins 50 km above Earth’s surface and ends at
80 km.
* The outer mesosphere temperatures approach 90°C.
* Most meteoroids burn up in the mesosphere,
producing meteor trails.
*
* The outermost layer of the atmosphere
* Extends from 80 km above Earth’s surface
outward into space.
* The air 80 km above Earth’s surface is only
about 0.001% as dense as the air at sea level.
* The thermosphere has no definite outer limit.
* Atmosphere does not end suddenly at the outer
edge of the thermosphere.
* Gas atoms and molecules there are so far apart
that the air blends gradually into outer space.
*
* Thermo- means “heat”.
* Even though the air in the thermosphere is
thin, it is very hot, up to 1,800°C.
* Energy from the sun strikes the thermosphere
first.
* Nitrogen and oxygen molecules convert energy
from the sun into heat.
*
* The outer layer of the thermosphere.
* Exo- means “outer”.
* The exosphere extends from 550 km outward
for thousand of kilometers.
* Satellites orbit in the exosphere making it
possible for you to make a long distance phone
call or watch television.
*
* All areas of the Earth do not receive the same
amount of light
* Earth is tilted 23.5° on its axis
* The angle the light hits the equator is more
direct than the areas away from the equator
* North and South Pole receive the least amount
of direct light
*
* Differences in the amount of tdirect light cause
differences in the amount of heat
* More direct light results in more hear that is
received
* Less direct results in less heat received
* Direct light decreases from the Equator to the Poles
* Since the Atmosphere is heated by conduction and
radiation from the water and land on Earth, the air
in the atmosphere above the equator is warmer
than the air over the north and south poles
*
*
*
* Describes how the volume changes with
changes in temperature when the pressure of a
gas is constant.
* When the temperature of a gas is increased at
constant pressure, it’s volume increases.
* When the temperature of a gas is decreased at
constant pressure, its volume decreases.
*
* Volume and density of air changes with changes
in temperature.
* As the temperature of air increases, its volume
increases and its density decreases.
* As the temperature of decreases, its volume
decreases and its density increases
*
* As air is heated its density decreases because
its mass remains constant but its volume
increases
* As air is cooled, its density increases because
its mass remains constant but its volume
decreases
*
* Air is fluid. Fluids that are dense sink below
those that are less dense (oil and water)
* The decreases in density as air is heated causes
it to rise above cooler, more dense air
* The increase in density as air is cooled causes
it to sink below warmer, less dense air
*
* The warmer air in the atmosphere rises and
cooler air in the atmosphere sinks. This causes
convection currents in the atmosphere.
*
*
Atmosphere
*Since air has mass, it also has other properties,
* density and pressure.
*The amount of mass in a given volume of air is
its density.
* Density=Mass ÷Volume (D = M /V)
*If there are more molecules in a given volume of
air, the density is greater.
*If there are fewer molecules, the density
decreases.
*
*Measured by meteorologists in units of millibars
(mb).
*The greater the millibars, the higher the
pressure
* Example: 1000 mb is a higher pressure than 500 mb.
*Pressure is the sum force pushing on an area or
surface of the Earth.
*P = ∑ F / A
* ∑ F= sum of forces
* A = area
*
*
*A denser substance
has more mass per
unit volume than a
less dense one.
*So denser air exerts
more pressure than
less dense air.
*Air pressure is the result
of the weight of a column
of air pushing down on an
area.
* The area has a pressure that
is higher than any place next
to it
* When air from the upper
atmosphere sinks it leaves an
“empty” spot
* When the sinking air reaches
lower levels it pushes some
air out of the way- it rises
and fills the “empty” spot
* Clear, Sunny, Calm Weather
*
* The area has a pressure that
is lower than any place next
to it
* When air close to the Earth’s
surface rises it leaves an
“empty” spot
* When the rising air reaches
higher levels it pushes some
air out of the way- it sinks
and fills the “empty’ spot
* Cloudy, Stormy Weather
*
* Areas that have the same pressure are
connected by a line called an isobar
*
* As air rises or is moved upward from the Earth
the pressure on the surface of the earth
decreases
* The force of air moving in an upward direction is
greater than the force exerted in a downward
direction
* Resulting in the area directly beneath the
rising air is lower in pressure- Low Pressure
System
*
* Air that sinks or moves downward from the
upper levels of the atmosphere causes the
pressure beneath the sinking air to increase
* The area directly below the sinking air has a
pressure that is higher than the areas that
surround it- High Pressure System
*
*Falling air pressure is usually indicates that a
storm is approaching.
*Rising air pressure usually means that the
weather is clearing.
*A barometer is an instrument that is used to
measure changes in air pressure.
*There are two kinds of barometers: mercury
barometers and aneroid barometers.
*
* A mercury barometer consists of a glass tube open at the
bottom end and partially filled with mercury.
* The space in the tube above the mercury is almost a
vacuum—it contains no air.
* The open end of the tube rests in a dish of mercury.
*
*
* The air pressure pushing down
on the surface of the mercury
in the dish is equal to the
weight of the column of
mercury in the tube.
* When the air pressure
increases, it presses down
more on the surface of
mercury.
* Greater air pressure forces the
column of mercury higher.
* When the air pressure
decreases the column of
mercury will fall
*The word aneroid means “without liquid”.
*An aneroid barometer has an airtight metal chamber.
* The metal chamber is sensitive to changes in air pressure
* When air pressure increases, the thin walls of the chamber are
pushed in.
* When the pressure drops, the walls bulge out.
*The changes in the walls of the metal chamber cause
the needle of the barometer to move
*
*
*Aneroid barometers are
smaller than mercury
thermometers.
*They don’t contain a
liquid.
*Therefore, they are
portable and often more
practical for uses such as
airplane instrument
panels.
* Wind is the horizontal movement of air between areas of
different pressure.
* The pressure gradient force is a force that is directed from
areas of high pressure to lower pressure.
* The pressure gradient force causes the initial movement of
air.
* PGF = area of higher pressure (mb) – area of lower pressure (mb)
distance between areas of pressure (km)
*
* Air that moves from the upper levels of the
atmosphere downwards towards Earth create
an area of high pressure beneath the falling air.
Air that rises or moves upwards from the Earth
or from lower levels of the atmosphere create
an area of low pressure beneath the rising air.
Cold air sinking would increase the pressure in
an area while warm air rising would decrease
the pressure in an area.
*
* When there are pressure differences in the
atmosphere air move from areas of high
pressure to areas of low pressure. This
movement of air creates wind
*
* Changes in pressure are measured with a
barometer.
* One type is the mercury barometer.
* As the pressure of an area increases in the
increased downward force of air pushes the
mercury in a barometer up into the barometer.
* As the pressure of the area decreases, the level
of mercury in a barometer falls because the
downward force of air on the liquid barometer
has decreased
*
*
Atmosphere
*Some places on Earth the atmosphere is calm
and there are few strong winds.
*These places develop over areas of the Earth
that are flat so that the air remains relatively
stationary and takes on the temperature and
humidity characteristics of the surface below.
*The bodies of air that develop over these areas
are called air masses.
*
*
* Scientists classify air masses
according to two
characteristics: temperature
and humidity.
* Whether an air mass is warm or
cold depends on the
temperature of the region over
which the air mass forms.
* Continental Artic
* Continental Polar
* Maritime Polar
* Maritime Tropical
* Continental Tropical
*
Type
Where it Forms
Temperature
Abbreviat
ion Used
Continental
Artic
Over the land that is
north of the artic circle
Very Cold
cA
Continental
Polar
Over the Northern plain
of Canada
Cold
cP
Maritime
Polar
Over the Northern
Atlantic and Pacific
Oceans
Cold
mP
Maritime
Tropical
Over the Southern
Warm
Atlantic Ocean and Gulf
of Mexico
mT
Continental
Tropical
Over the land of the U.S Warm
Southwest desert and
northern Mexico
cT
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* Air Masses do not remain
stationary
* Winds high in the
atmosphere such as the jet
stream and other with and
high and low pressure
centers move air masses
* As air masses move over
other areas they take on the
temperature and humidity
of the surface beneath
* The more water an air mass
contains, the more moist or
humid it is
* The less water an air
contains the more dry it is
* Air masses then to collide in
the middle latitudes (30-60
degrees)
* When Air Masses collide they
form a Front
*Something happens when two air masses with
different temperatures and densities collide.
*The area where the air masses meet and do not
mix becomes a front.
*When air masses meet at a front, the collision
often causes storms and changeable weather.
*There are four types of fronts: cold fronts,
warm fronts, stationary fronts, and occluded
fronts.
*
*
*When a rapidly moving cold air mass runs into a
slowly moving warm air mass, the denser cold
air slides under the lighter warm air.
*The warm air is pushed upward. The front that
forms is called a cold front.
*Cold fronts move quickly, so they can cause
abrupt weather changes, including violent
thunderstorms.
*After a cold front passes through an area, cool,
dry air moves in, often bringing clear skies and
cooler temperatures.
*
*Clouds, storms, and rain also accompany warm fronts.
*At a warm front, a moving air mass collides with a
slowly moving cold air mass.
*Because cold air is more dense than warm air, the warm
air moves over the cold air.
*Because warm fronts move more slowly than cold fronts,
the weather may be rainy or foggy for several days
*After a warm front passes through an area, the weather
is likely to be warm and humid.
*In winter, warm fronts bring snow.
*
*
*Sometimes cold and
warm masses meet,
but neither one has
enough force to move
the other.
*Where the warm and
cool air meet, water
vapor in the warm
air condenses into
rain, snow, fog, or
clouds.
*a warm air mass is
caught between two
cooler air masses The
denser cool air masses
move underneath the
less dense warm air
mass and push it
upward
*As the warm air cools
and its water vapor
condenses, the
weather may turn
cloudy and rainy or
snowy.
*
*
*
* Different Air Masses can
contain different amounts of
water vapor
* If the rate of evaporation is
greater than the rate of
condensation, more water
will exist as water vapor
* If the rate of condensation
is greater than the rate of
evaporation, more water
will exist in the liquid form
* When water vapor
condenses it can form
Clouds and different forms
of precipitation
* Rain
* Hail
* Snow
* Sleet
* Three factors are necessary for precipitation to occur include
* differences in density between the warm and cold air masses,
* an upper atmosphere that has temperatures lower than the air in
the rising warm air mass and
* a significant amount of water vapor in the rising warm air mass
*
Density differences
* The temperature
of the atmosphere decreases with
the height of the atmosphere. When cold fronts
form, air from the cold and warm air masses move as
a result of their densities.
* The more dense cold air pushes under the less dense
warm air ahead of it. The air in the warm air mass
rises
* As the warm air rises, it encounters cooler
temperatures and the rate of evaporation decreases.
* As the rate of evaporation becomes slower than the
rate of condensation any water vapor in the warm air
condenses and forms clouds and precipitation
*
Temperature changes
* When warm fronts form, air from the cold and warm air
masses moves as a result of their densities.
* The less dense warm air behind the cold air masses rises
and slide over and above the cold air mass
* As the warm air rises it encounters cooler temperatures
and the rate of evaporation decreases.
* As a the rate of evaporation becomes slower than the rate
of condensation, any water vapor in the warmer air can
condense and form clouds and precipitation
*
Amount of Water Vapor
* The more water vapor the rising warm air mass
contains, the more likely it is that there will be
a greater amount of precipitation than occurs
with both a warm and cold front
*
* If fronts are formed between air masses that contain more
moisture then more precipitation may occur.
* Warm air mass over land creates a warm DRY air mass- desert
* Warm air mass over water creates a MOIST air mass
* The rising of the warm DRY air mass into the upper levels of
the atmosphere produced LESS precipitation
* A front formed by a cold DRY air mass and a warm MOIST air
mass will likely produce MORE precipitation than a front
formed between a cold DRY air mass and a warm DRY air mass
* The meeting of a cold MOIST air mass and a warm MOIST air
mass would likely produced MORE precipitation than that
produced by the meeting of a cold MOIST and a warm DRY air
mass
*
* In both cold and warm fronts, rising of the warmer air
mass is accompanied by a decrease in the atmospheric
pressure
* In cold front, there is a decrease in pressure as the
front forms because the cool air mass slides under the
warmer air mass and pushes it upward
* The rising warm air results in a decrease in
atmospheric pressure
* This decrease is followed by an increase in pressure
once the front has passed because of the cooler sinking
air that moved in behind the warmer rising air
*
* In a warm front, there is a decline in the
atmospheric pressure as the front moves into
an area because a warm air mass moves in
behind a cooler air mass
* As the Warm air mass slides over the cooler air
mass there is a decrease in pressure
* The pressure continues to drop as the front
passes because of the warmer, rising air that
moved in behind the cooler air mass
*