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 -- Wind Speed and Direction

-- Pressure -- Precipitation

-- Cloud Cover

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.

The Atmosphere: Structure and Temperature

Composition of the Atmosphere

• 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)

• 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.

Weather or Climate???

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 atmosphereNitrogen (N2)-

78%, Oxygen (O2)-

21%,Carbon Dioxide

(CO2) 0.03 %,

Where did all the oxygen come from?

• 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.

Modern atmosphere

Photosynthetic organisms evolve. (cyanobacteria)

These organisms use CO2 and produce oxygen (O2) as a waste product.

• 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

Modern atmosphere

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)

Green House Gases

Atmosphere Characteristics

varies from 4% to less than 1%

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

Aneroid Barometers: (without liquid)

Barometer - apparatus used to measure pressure;  is derived from the Greek "baros" meaning "weight" 

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. Altitude120

110

100

80

70

60

50

40

30

20

10

90

0

-120 -100 -80 -60 -40 -20 0 20 40 60

THERMOSPHERE

Mesopause

MESOPHERE

Stratopause

STRATOSPHERE

Tropopause

TROPOSPHERE

Hei

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COLDER WARMER

The atmosphere

is divided into

layers based on

temperature.

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:

Remove heat -> molecules move slower -> temperature falls.

•Add heat -> molecules move faster -> temperature rises

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 is the transfer of heat through matter by molecular activity.

Conduction

• Convection is the transfer of heat by mass movement or circulation within a substance.

Convection

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

conduction

temperature

convection

heat

troposphere

stratosphere

ozone

mesosphere

radiation

VOCABULARY

ionosphere

thermosphere

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.

30 units reflected or scattered back to space

Atmosphere absorbs 19 units

Earth’s surfaceabsorbs 51 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

Conduction and convection transfer 7 units to atmosphere

Evaporationtransfers 23 units to atmosphere

100 units of

Insolation

Earth’s Earth’s heat heat

budgetbudget represents represents

the flow of energy the flow of energy

into and out of into and out of

Earth’s Earth’s

atmosphere.atmosphere.

An An imbalanceimbalance in in

Earth’s heat budget Earth’s heat budget

changes Earth’s changes Earth’s

mean temperature.mean temperature.

SOLAR RADIATIONSOLAR 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!

SOLAR RADIATION

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.

VOCABULARY

Local Temperature VariationsAtmosphere

Equator The angle of sunlight varies with latitude.

isotherm

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

Tilt of Earth’s Axis

Insolation: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 AxisAltitude 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’SRAYS

New Orleans

EquatorEquator

New Orleans

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.

Earth’s Motions• Earth has two principal motions—rotation and

revolution.

Rotation = 24 hoursRevolution = 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.

Land and Water• Land heats more rapidly and to higher temperatures

than water. Land also cools more rapidly and to lower temperatures than water.

Geographic Position• The geographic setting can greatly influence

temperatures experienced at a specific location.

Temperature Controls

• 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

What determines temperature?

The Effect of the Ocean on Annual Temperature

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 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.

Clouds Reflect and Absorb 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

• Ultraviolet10-9 – 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