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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

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Basic Properties of the Atmosphere

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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 -- Wind Speed and Direction
        • -- Pressure -- Precipitation
        • -- Cloud Cover
the atmosphere structure and temperature
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.

Climatology: study of climate types and patterns and the causes of those patternsClimate: sum of all statistical weather info that helps describe a place or regionSlowly - varyingAverages (monthly, yearly)Ranges (largest value - smallest value)Extremes (maximum, minimum)

Composition of the Atmosphere

weather or climate
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
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
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
Modern atmosphere

Nitrogen (N2)-


Oxygen (O2)-


Carbon Dioxide (CO2) 0.03 %,

Where did all the oxygen come from?

modern atmosphere1
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 atmosphere2
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
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%)

Helium (He)(0.000524%)

Methane (CH4)(0.0001745%)

Krypton (Kr)(0.000114%)

Hydrogen (H2)

varies from 4% to less than 1%

Green House Gases

atmosphere characteristics1
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
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.

observing the atmosphere
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
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











Height above ground (kilometers)























Atmospheric Pressure vs. Altitude

The atmosphere is divided into layers based on temperature.

structure of the atmosphere
Structure of the Atmosphere
  • Defined by Temperature Profiles
  • Troposphere
    • Where Weather Happens
  • Stratosphere
    • Ozone Layer
  • Mesosphere
  • Thermosphere
    • Ionosphere
atmosphere characteristics2
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 characteristics3
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.

heating 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 atmosphere1
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
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 temperature1
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
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
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
Converting F to C – In Your Head
  • Subtract 32
  • Add the first Digit
  • Divide by two

°F = 1.8 (°C) + 32

absolute temperature
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 atmosphere1
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 atmosphere2
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.

heating the atmosphere3
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
Energy Transfer as Heat














heating the atmosphere4
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 atmosphere5
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 atmosphere6
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 atmosphere7
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.

100 units of insolation


6 units radiate to space from Earth’s surface

30 units reflected or scattered back to space

A total of 64 units radiated back into space via the atmosphere

Atmosphere absorbs 19 units

15 units radiate from surface to atmosphere



23 units to


Earth’s surface

absorbs 51 units

Conduction and convection

transfer 7 units to atmosphere

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.

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
Local Temperature Variations


The angle of sunlight varies with latitude.



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.


A line drawn on a weather map through places having the same atmospheric temperature at a given time.

tilt of earth s axis
Tilt of Earth’s Axis


The solar (energy) radiation that reaches Earth.

reaches Earth.

**The Axial Tilt of the Earth is the cause of the seasons.

tilt of earth s axis1
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).










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
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 characteristics4
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 characteristics5
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
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 controls1
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
17 3 temperature controls

Why Temperatures Vary

17.3 Temperature Controls

 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 radiation1
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
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
  • 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
  • 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
  • 50 – 80 km altitude
  • Temperature decreases with altitude
  • 0 C at base, -95 C at top
  • Top is coldest region of atmosphere
  • 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
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
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
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
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
Atmospheric Measurements
  • Temperature
  • Pressure
  • Humidity
  • Wind Velocity and Direction
weather instruments
Weather Instruments
  • Temperature: Thermometer
  • Pressure: Barometer
  • Humidity: Hygrometer
  • Wind Velocity and Direction:

Anemometer and Wind Vane

  • Fluid
    • Mercury
    • Alcohol
    • Use expansion of fluid
  • Bimetallic
    • Differential expansion of different metals
  • Electronic
    • Electrical resistance change with temperature
  • 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
  • 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
  • Balloons carry radiosondes
    • Thermometer
    • Barometer
    • Hygrometer
    • Transmitter
  • Typically reach 30 km before balloon breaks
  • Detect precipitation types and amounts
  • Doppler radar measures velocity of winds
satellite studies
Satellite Studies
  • Visual imagery
  • Infrared imagery
  • Laser spectroscopy
earth s radiation budget
Earth’s Radiation Budget
  • What comes in must go out
  • Direct Reflectance (Short Wave)
    • 31%
  • Infrared Re-emission (Long Wave)
    • 69%
how heat moves
How Heat Moves
  • Radiation
  • Conduction
  • Convection

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%