Download The Atmosphere - CoconinoHighSchool

Basic Properties of the
Atmosphere
The Atmosphere: Structure and
Temperature
Meteorology: the study of the physics, chemistry, and
dynamics (movement) of the Earth’s atmosphere
–Atmosphere: Envelope of gases bound to the Earth by
gravity
–Weather: State of the atmosphere at a given time
and place; constantly changing
•Weather is described by variables such as:
-- Temperature
-- Pressure
-- Cloud Cover
-- Wind Speed and Direction
-- Precipitation
The Atmosphere: Structure and
Temperature
 Weather is constantly changing, and it refers
to the state of the atmosphere at any given
time and place.
 Climate, however, is based on observations
of weather that have been collected over
many years. Climate helps describe a place
or region.
Composition of the Atmosphere
• Climatology: study of climate types and
patterns and the causes of those
patterns
Climate: sum of all statistical weather info that
helps describe a place or region
Slowly - varying
Averages (monthly, yearly)
Ranges (largest value - smallest value)
Extremes (maximum, minimum)
Weather or Climate???
• The average high temperature for the month of
July in Phoenix is 111oF.
• Cumulus clouds presently cover the entire sky.
• Snow is falling at a rate of 1 inch per hour.
• The summers here are warm and humid.
• At 3:00 p.m, winds were blowing from the NW at
10 mph.
• Total precipitation at O’Hare Airport for 2003
was 32.02 inches, which is 4.25 inches below
normal.
Origin of the atmosphere
• The original atmosphere
– Probably made up of hydrogen and helium.
– These are fairly common in the universe.
• Original atmosphere stripped away by the solar
wind
– H and He are very light
• Hydrogen and helium have the smallest atoms by mass.
– The early earth was not protected by a magnetic field.
– Thus the current atmosphere is considered a
secondary atmosphere
The secondary atmosphere
• Formed from degassing of
volcanoes
• Gasses emitted probably
similar to the gasses emitted by
volcanoes today.
– H2O (water), 50-60%
– CO2 (carbon dioxide), 24%
– SO2 (sulfur dioxide), 13%
–
–
–
–
–
–
–
CO (carbon monoxide),
S2 (sulfur),
Cl2 (chlorine),
N2 (nitrogen),
H2 (hydrogen),
NH3 (ammonia) and
CH4 (methane)
Modern atmosphere
Nitrogen (N2)78%,
Oxygen (O2)21%,
Carbon Dioxide
(CO2) 0.03 %,
Where did all the oxygen come from?
Modern atmosphere
• Life changes the
atmosphere
• With the evolution of
life the first cellular
organisms began to
use the gasses in the
early atmosphere
NH3 – ammonia,
CH4 – methane,
H2O – water for energy.
Photosynthetic organisms
evolve. (cyanobacteria)
These organisms use CO2
and produce oxygen (O2) as a
waste product.
Modern atmosphere
• Where did the O2 come from?
– Produced by photosynthetic life.
• Where did the CO2 go?
– Dissolves in water in the oceans
– Used by life by photosynthesis and buried
when plants and micro-organisms die.
• The source of coal and oil
Atmosphere Characteristics
Permanent gases:
Variable gases:
(together 99.96%)
(N) Nitrogen 78%
(CO2) Carbon dioxide
(O) Oxygen 21%
(O3) Ozone
(Ar) Argon ~ .9%
(H2O) Water vapor Neon (Ne)(0.001818%)
varies from 4% to less
Helium (He)(0.000524%)
than 1%
Methane (CH4)(0.0001745%)
Krypton (Kr)(0.000114%)
Green House Gases
Hydrogen (H2)
Atmosphere Characteristics
 Variable Components
• Water vapor is the source of all clouds and
precipitation. Like carbon dioxide, water vapor
absorbs heat given off by Earth. It also absorbs
some solar energy.
• Ozone is a form of oxygen that combines three
oxygen atoms into each molecule (O3).
• If ozone did not filter most UV radiation and all of
the sun’s UV rays reached the surface of Earth,
our planet would be uninhabitable for many
living organisms.
Atmospheric Structure
 The atmosphere rapidly thins as you travel
away from Earth until there are too few gas
molecules to detect.
 Pressure Changes
• Atmospheric pressure
is simply the weight of
the air above.
 Pressure Changes
 Pressure Changes
Observing the Atmosphere
• Air Pressure: force per area exerted by
the mass of air above a point
• Measured in:
– Inches of mercury (in. Hg)
– Millibars (mb)
• Average sea-level pressure = 1013.25 mb
or 29.92 in. Hg
• Air pressure is Measured using a
barometer
Mercury Barometer
Barometer - apparatus used
to measure pressure; is
derived from the Greek "baros"
meaning "weight"
Aneroid Barometers: (without liquid)
Air Pressure
• By lucky coincidence, earth’s atmospheric
pressure is approximately neat round
numbers in metric terms
• 14.7 pounds per square inch (1 kg/cm2)
• Pressure of ten meters of water
• Approximately one bar or 100 kPa
• Weather reports use millibars (mb)
• One mb = pressure of one cm water
Atmospheric Pressure vs. Altitude
120
110
Height above ground (kilometers)
100
The atmosphere
is divided into
layers based on
temperature.
THERMOSPHERE
90
Mesopause
80
70
MESOPHERE
60
50
Stratopause
40
30
STRATOSPHERE
20
Tropopause
10
TROPOSPHERE
0
-120
COLDER
-100
-80
-60
-40
-20
0
20
40
60
WARMER
Structure of the Atmosphere
• Defined by Temperature Profiles
• Troposphere
– Where Weather Happens
• Stratosphere
– Ozone Layer
• Mesosphere
• Thermosphere
– Ionosphere
Atmosphere Characteristics
 Temperature Changes
• The atmosphere can be divided vertically into four
layers based on temperature.
• The troposphere is the bottom layer of the
atmosphere where temperature decreases with an
increase in altitude.
• The stratosphere is the layer of the atmosphere
where temperature remains constant to a height
of about 20 kilometers. It then begins a gradual
increase until the stratopause.
Atmosphere Characteristics
 Temperature Changes
• The mesosphere is the layer of the atmosphere
immediately above the stratosphere and is
characterized by decreasing temperatures with
height.
• The thermosphere is the region of the
atmosphere immediately above the mesosphere
and is characterized by increasing temperatures
due to the absorption of very short-wave solar
energy by oxygen.
Thermal Structure of the Atmosphere
Heating the Atmosphere
 Heat is the energy transferred from one
object to another because of a difference in
the objects’ temperature.
 Temperature is a measure of the average
kinetic energy of the individual atoms or
molecules in a substance.
Observing the Atmosphere
• Temperature: measure of the
motion of the molecules in a
substance
– Hot air: molecules moving
more quickly
– Cold air: molecules moving
less quickly
– Measured using a
thermometer
– Always measured in shady
conditions
– Units: oC, oF
Heat and Temperature
• Temperature: Average energy of
molecules or atoms in a material
• Heat: Total energy of molecules or atoms
in a material
• Can have large amount of heat but low
temperatures
• Can have high temperatures but little heat
Heat and Temperature
• The Arctic Ocean has a large amount of
heat (because of large mass) even though
the temperature is low.
• Air in an oven at 500 F has high
temperature but little heat.
• However, touch anything solid in the oven,
and you’ll get burned. Same temperature,
much larger amount of heat.
HEAT & TEMPERATURE
• Heat is a measure of energy.
• Matter is composed of atoms & molecules that are
constantly vibrating and
• Heat = total kinetic energy of atoms & molecules
• By contrast, Temperature is a measure of intensity.
• Temperature = average kinetic energy of individual
atoms and molecules.
• Heat and Temperature are of course closely related:
•Add heat -> molecules move faster -> temperature rises
Remove heat -> molecules move slower -> temperature
falls.
Temperature Scales
• Fahrenheit
– Water Freezes at 32 F
– Water Boils at 212 F
• Centigrade or Celsius
– Water Freezes at 0 C
– Water Boils at 100 C
• Two scales exactly equal at -40
Converting C to F – In Your Head
• Double the Centigrade
• Subtract the first Digit
• Add 32
°C = (°F – 32) / 1.8
Converting F to C – In Your Head
• Subtract 32
• Add the first Digit
• Divide by two
°F = 1.8 (°C) + 32
Absolute Temperature
• Once atoms stop moving, that’s as
cold as it can get
• Absolute Zero = -273 C = -459 F
• Kelvin scale uses Celsius degrees and
starts at absolute zero
• Most formulas involving temperature
use the Kelvin Scale
Heating the Atmosphere
 Three mechanisms of energy transfer as
heat are conduction, convection, and
radiation.
 Conduction
• Conduction is the transfer of heat through
matter by molecular activity.
 Convection
• Convection is the transfer of heat by mass
movement or circulation within a substance.
Heating the Atmosphere
 Electromagnetic Waves
• The sun emits light and heat as well as the ultraviolet
rays that cause a suntan. These forms of energy are
only part of a large array of energy emitted by the sun,
called the electromagnetic spectrum.
Visible Light Consists
of an Array of Colors
Heating the Atmosphere
 Radiation
• Radiation is the transfer of energy (heat)
through space by electromagnetic waves that
travel out in all directions.
• Unlike conduction and convection, which need
material to travel through, radiant energy can
travel through the vacuum of space.
Energy Transfer as Heat
VOCABULARY
radiation
conduction
convection
temperature
heat
troposphere
stratosphere
ozone
mesosphere
thermosphere
ionosphere
insolation
Heating the Atmosphere
 Radiation
• All objects, at any temperature, emit radiant
energy.
• Hotter objects radiate more total energy per unit
area than colder objects do.
• The hottest radiating bodies produce the shortest
wavelengths of maximum radiation.
• Objects that are good absorbers of radiation are
good emitters as well.
Heating the Atmosphere
 When radiation strikes an object, there
usually are three different results.
1. Some energy is absorbed by the object.
2. Substances such as water and air are
transparent to certain wavelengths of radiation.
3. Some radiation may bounce off the object
without being absorbed or transmitted.
Heating the Atmosphere
 Reflection and Scattering
• Reflection occurs when light bounces off an
object. Reflection radiation has the same
intensity as incident radiation.
• Scattering produces a larger number of weaker
rays that travel in different directions.
Heating the Atmosphere
 Absorption
• About 50 percent of the solar energy that strikes
the top of the atmosphere reaches Earth’s
surface and is absorbed.
• The greenhouse effect is the heating of Earth’s
surface and atmosphere from solar radiation
being absorbed and emitted by the atmosphere,
mainly by water vapor and carbon dioxide.
SOLAR RADIATION
100 units of
Insolation
Earth’s heat
budget represents
the flow of energy
into and out of
Earth’s
atmosphere.
An imbalance in
Earth’s heat budget
changes Earth’s
mean temperature.
30 units reflected or
scattered back to
space
Atmosphere
absorbs 19
units
A total of 64 units
radiated back into
space via the
atmosphere
6 units radiate
to space from
Earth’s surface
15 units radiate
from surface to
atmosphere
Evaporation
transfers
23 units to
atmosphere
Earth’s surface
absorbs 51 units
Conduction and convection
transfer 7 units to
atmosphere
SOLAR RADIATION
About 50% of the incoming solar radiation is absorbed by the
Earth’s surface. Most of the molecules in the Earth’s
atmosphere do not absorb visible or shortwave radiation.
The Earth’s surface warms, and emits energy in the form of
infrared or longwave radiation, which is invisible to the
human eye.
Certain molecules in the atmosphere, called greenhouse
gases, do absorb the Earth’s infrared radiation. This
absorption warms the atmosphere.
Also, the greenhouse gas molecules emit their own infrared
radiation, which is absorbed by other molecules, and the
atmosphere warms even more!
Local Temperature Variations
Atmosphere
VOCABULARY
isotherm
A line drawn
on a weather
map through
places having
the same
atmospheric
temperature
at a given
time.
The intensity of insolation depends upon the
angle at which sunlight strikes Earth’s
surface. The intensity is greatest at low
latitudes, during the summer, and around
noon.
The angle of sunlight varies with
latitude.
Tilt of Earth’s Axis
reaches Earth.
Insolation:
The solar (energy)
radiation that
reaches Earth.
**The Axial Tilt
of the Earth is
the cause of the
seasons.
Tilt of Earth’s Axis
Altitude of sun affects amount of energy
received at surface because
lower angle -> more
spread out and less
intense radiation
(as for flashlight
beam).
lower angle -> more
of atmosphere to
pass through, and
hence more chance to
be absorbed or
reflected
(can look at sun at
sunset).
SUN’S
RAYS
June 21
Dec. 21
During the summer, the Northern Hemisphere is tilted
towards the Sun. Here, locations receive the Sun’s most
direct rays, and have longer periods of daylight hours.
During the winter, the Northern Hemisphere is tilted away
from the Sun. Periods of daylight are shorter, and the
Sun’s rays are less direct.
Solstices and Equinoxes
During the vernal
(spring) and
autumnal (fall)
equinoxes, neither
hemisphere is
tilted towards or
away from the
Sun. On these
dates, every
location on Earth
receives 12 hours
of daylight and 12
hours of darkness.
Atmosphere Characteristics
 Solstices and Equinoxes
• The summer solstice is the solstice that occurs
on June 21 or 22 in the Northern Hemisphere
and is the “official” first day of summer.
• The winter solstice is the solstice that occurs on
December 21 or 22 in the Northern Hemisphere
and is the “official” first day of winter.
Atmosphere Characteristics
 Solstices and Equinoxes
• The autumnal equinox is the equinox that
occurs on September 22 or 23 in the Northern
Hemisphere.
• The spring equinox is the equinox that occurs
on March 21 or 22 in the Northern Hemisphere.
Temperature Controls
 Earth’s Motions
• Earth has two principal motions—rotation and
revolution.
Rotation = 24 hours
Revolution = 365 days
 Earth’s Orientation
• Seasonal changes occur because Earth’s
position relative to the sun continually changes
as it travels along its orbit.
Temperature Controls
 Factors other than latitude that exert a strong influence
on temperature include heating of land and water,
altitude, geographic position, cloud cover, and ocean
currents.
 Geographic Position
• The geographic setting can greatly influence
temperatures experienced at a specific location.
 Land and Water
• Land heats more rapidly and to higher temperatures
than water. Land also cools more rapidly and to
lower temperatures than water.
Temperature Controls
What determines temperature?
• Latitude: locations at lower latitudes typically
experience higher temps year-round than higher
latitude locations, because the lower latitudes
receive more solar energy
• Proximity to water: locations near water,
especially a cool ocean current, have smaller
annual temp ranges than landlocked locations
• Elevation: locations at higher elevations (altitude)
usually have cooler conditions than locations at
lower elevations
The Effect of the Ocean on Annual
Temperature
17.3 Temperature Controls
Why Temperatures Vary
 Cloud Cover and Albedo
• Albedo is the fraction of total radiation that is
reflected by any surface.
• Many clouds have a high albedo and therefore
reflect back to space a significant portion of the
sunlight that strikes them.
Clouds Reflect and Absorb Radiation
Clouds Reflect and Absorb Radiation
Clouds
•On Earth, water naturally occurs in all 3
phases or states of matter (gas, liquid, solid)
•Clouds are composed of tiny liquid water
droplets or tiny ice crystals.
–Clouds are not made of water vapor (Otherwise,
we wouldn’t be able to see them!)
•In nature, clouds form when the temperature
of air is lowered to its dewpoint temperature.
Electromagnetic Radiation
•
•
•
•
•
•
•
Radio: cm to km wavelength
Microwaves: 0.1 mm to cm
Infrared:
0.001 to 0.1 mm
Visible light 0.0004 – 0.0007 mm
Ultraviolet 10-9 – 4 x 10-7 m
X-rays 10-13 – 10-9 m
Gamma Rays
10-15 –10-11 m
Troposphere
• Heating of the Surface creates warm air at
surface
• Warm air rises, but air expands as it rises
and cools as it expands (Adiabatic cooling)
• Heating + Adiabatic Cooling = Warm air at
surface, cooler air above
• Buoyancy = Cool air at surface, warmer air
above
• Two opposing tendencies = constant
turnover
Stratosphere
•
•
•
•
Altitude 11-50 km
Temperature increases with altitude
-60 C at base to 0 C at top
Reason: absorption of solar energy to
make ozone at upper levels (ozone layer)
• Ozone (O3) is effective at absorbing solar
ultraviolet radiation
Mesosphere
•
•
•
•
50 – 80 km altitude
Temperature decreases with altitude
0 C at base, -95 C at top
Top is coldest region of atmosphere
Thermosphere
• 80 km and above
• Temperature increases with altitude as
atoms accelerated by solar radiation
• -95 C at base to 100 C at 120 km
• Heat content negligible
• Traces of atmosphere to 1000 km
• Formerly called Ionosphere
Why is the Mesosphere so Cold?
• Stratosphere warmed because of ozone
layer
• Thermosphere warmed by atoms being
accelerated by sunlight
• Mesosphere is sandwiched between two
warmer layers
Composition and Altitude
• Up to about 80 km, atmospheric
composition is uniform (troposphere,
stratosphere, mesosphere)
• This zone is called the homosphere
• Above 80 km light atoms rise
• This zone is sometimes called the
heterosphere
Mean Free Path
• Below 80 km, an atom accelerated by
solar radiation will very soon hit another
atom
• Energy gets evenly distributed
• Above 80 km atoms rarely hit other atoms
• Light atoms get accelerated more and fly
higher
• Few atoms escape entirely
Planets and Atmospheres
• At top of atmosphere, an atom behaves
like any ballistic object
• Velocity increases with temperature
• If velocity exceeds escape velocity, atom
or molecule escapes
• Earth escape velocity 11 km/sec.
• Moon escape velocity 2.4 km/sec
Atmospheric Measurements
•
•
•
•
Temperature
Pressure
Humidity
Wind Velocity and Direction
Weather Instruments
•
•
•
•
Temperature:
Thermometer
Pressure:
Barometer
Humidity:
Hygrometer
Wind Velocity and Direction:
Anemometer and Wind Vane
Thermometers
• Fluid
– Mercury
– Alcohol
– Use expansion of fluid
• Bimetallic
– Differential expansion of different metals
• Electronic
– Electrical resistance change with temperature
Barometers
• Mercury
– Air pressure will support 10 meters of water
– Mercury is 13 times denser
– Air pressure will support 76 cm of mercury
• Aneroid
– Air pressure deforms an evacuated chamber
Hygrometers
• Filament
– Hair expands and contracts with humidity
• Sling Psychrometer
– Measures cooling by evaporation
– Two thermometers
– Wet bulb and Dry bulb
• Electrical
– Chemicals change resistance as they absorb
moisture
Sounding
• Balloons carry radiosondes
– Thermometer
– Barometer
– Hygrometer
– Transmitter
• Typically reach 30 km before balloon
breaks
Radar
• Detect precipitation types and amounts
• Doppler radar measures velocity of winds
Satellite Studies
• Visual imagery
• Infrared imagery
• Laser spectroscopy
Earth’s Radiation Budget
• What comes in must go out
• Direct Reflectance (Short Wave)
– 31%
• Infrared Re-emission (Long Wave)
– 69%
How Heat Moves
• Radiation
• Conduction
• Convection
Albedo
Albedo = % incident energy reflected by a
body
• Fresh snow: 75 – 95%
• Old snow: 40 – 60%
• Desert:
25 – 30%
• Deciduous forest, grassland: 15 – 20%
• Conifer forest:
5 – 15%
• Camera light meters set to 18%
Global Albedo