Chapter 11 Heating the Atmosphere

Earth’s Unique Atmosphere

No other planet in our solar system has an atmosphere with the exact mixture of gases or the heat and moisture conditions necessary to sustain life as we know it.

Introduction of Weather

Weather influences our everyday activities, our jobs, and our health and comfort.

Many of us pay little attention to the weather unless we are inconvenienced by it or when it adds to our enjoyment outdoors.

Weather Continued(Severe weather events)

United States has the greatest variety of weather of any country in the world.

Tornadoes Flash Floods Intense Thunderstorms Hurricanes Blizzards

Weather and Climate

Weather Weather is over a short period of

time Constantly changing

Climate Climate is over a long period of

time Generalized, composite of

weather

Weather and Climate

Elements of weather and climate Properties that are measured

regularly Most important elements

Temperature Humidity Cloudiness Precipitation Air Pressure Winds speed and direction

Composition of the Atmosphere

Air is a mixture of discrete gases

Major components of clean, dry air Nitrogen (N)—78% Oxygen (O2)—21% Argon and other gases Carbon dioxide (CO2)—0.036%—

absorbs heat energy from Earth

Composition of Dry Air

Composition of the Atmosphere

Variable components of air Water vapor

Up to about 4% of the air's volume Forms clouds and precipitation Absorbs heat energy from Earth

Aerosols Tiny solid and liquid particles Water vapor can condense on solids Reflect sunlight Help color sunrise and sunset

Composition of the Atmosphere

Variable components of air Ozone

Three atoms of oxygen (O3) Distribution not uniform Concentrated between 10 to 50

kilometers above the surface Absorbs harmful UV radiation Human activity is depleting ozone by

adding chlorofluorocarbons (CFCs)

Chlorofluorocarbons (CFCs)

Over the past half century, people have unintentionally placed the ozone layer in jeopardy by polluting the atmosphere.

Many uses developed for CFCs • Coolants for AC• Refrigeration equipment• Cleaning solvents for electronic components

and comp. chips• Propellants for aerosol sprays

Characteristics of CFCs Practically inert, not chemically

active in the lower atmosphere Gradually make their way to the

ozone layer Sunlight separates the chemicals

into their constituent atoms Chlorine atoms released, breaking

up some of the ozone molecules

Importance of Ozone Ozone filters out most of the UV radiation

from the Sun Decreased concentration allows more of

these harmful wavelengths to reach Earth’s surface

Increase risks of skin cancer Impair the human immune system Promote cataracts, clouding of the eye lens that

reduces vision. May cause blindness if not treated

Montreal Protocol was developed under the sponsorship of the UN to eliminate the production and use of CFCs

Structure of the Atmosphere

Pressure changes Atmospheric Pressure is the

weight of the air above Average sea level pressure

Slightly more than 1000 millibars About 14.7 pounds per square inch

Pressure decreases with altitude One half of the atmosphere is below

3.5 miles (5.6 km) Ninety percent of the atmosphere is

below 10 miles (16 km)

Atmospheric Pressure Variation

with Altitude

Figure 11.5

Structure of the Atmosphere

Atmospheric layers based on temperature Troposphere

Bottom layer, where all weather phenomena occur

Temperature decreases with altitude—Called the environmental lapse rate

6.5˚C per kilometer (average) 3.5˚F per 1000 feet (average)

Thickness varies with latitude and season—Average height is about 12 km

Outer boundary is named the tropopause

Structure of the Atmosphere

Atmospheric layers based on temperature Stratosphere

About 12 km to 50 km Temperature increases at top due to ozone

absorbing UV radiation from the sun Outer boundary is named the stratopause

Mesosphere About 50 km to 80 km Temperature decreases Outer boundary is named the mesopause

Structure of the Atmosphere

Atmospheric layers based on temperature Thermosphere

No well-defined upper limit Fraction of atmosphere's mass Gases moving at high speeds

Temperatures in the Thermosphere

Increases with altitude, absorption of very shortwave high-energy solar radiation by atoms of oxygen and nitrogen

Rising to extreme values of more than 1000 degrees Celsius

Temperature is defined in term of average speed at which molecules move

Sparse amount of gases = insignificant quantity of heat

Thermal Structure of the Atmosphere

Figure 11.7

Earth–Sun Relations

Earth’s two principal motions Rotates on its axis, an imaginary line running

through the poles One rotation/24 Hrs. Cycle of daylight and darkness

Revolves around the Sun Hundred years ago, most people believed Earth

was stationary, Sun/stars revolved around Earth Fact: Traveling at more than 107,000 km/hr

orbiting about the sun Seasons

Result of Changing Sun angle Changing length of daylight

Seasons Result of

Changing Sun angle At around 90 degrees angle, the solar rays

are more concentrated At a lesser angle, the solar rays are more

spread out, and therefore less intense solar radiation that reaches the surface

Thickness of atmosphere, lower the angle, the more distance the rays have to penetrate

The longer the path, the greater the chances that sunlight will be absorbed, reflected, or scattered by the atmosphere, reduce intensity at the surface

Changing length of daylight Longer the day, the more solar radiation the

Earth takes in

Daily Paths of the Sun at 40° N latitude—June

Figure 11.9 A

Daily paths of the Sun at

40° N latitude—December

Figure 11.9 B

Relationship of Sun Angle and Intensity of Solar

Radiation

Figure 11.10

Earth–Sun Relations

Seasons Caused by Earth's changing

orientation to the Sun Axis is inclined 23½° Axis is always pointed in the same

direction Special days (Northern

Hemisphere) Summer solstice

June 21–22 Sun's vertical rays are located at the

tropic of Cancer (23½° N latitude)

Earth–Sun relations

Seasons Special days (Northern

Hemisphere) Winter solstice

December 21–22 Sun's vertical rays are located at the

tropic of Capricorn (23½° S latitude) Autumnal equinox

September 22–23 Sun's vertical rays are located at the

equator (0° latitude)

Earth–Sun relations

Seasons Special days (Northern

Hemisphere) Spring equinox

March 21–22 Sun's vertical rays are located at

the equator (0° latitude)

Earth–Sun Relationships

Characteristics of the Solstices and

Equinoxes

Atmospheric Heating Heat is always transferred

from warmer to cooler objects Mechanisms of heat transfer

Conduction through molecular activity

Convection Mass movement within a substance

Radiation (electromagnetic radiation) Velocity: 300,000 kilometers (186,000

miles) per second in a vacuum

Conduction Transfer of heat through matter by

molecular activity Energy of molecules is transferred

through collisions from one molecule to another, heat flowing from high to low temp.

Metals are good conductors Air is a very poor conductor of heat Conduction is the least significant of the

three as a means of heat transfer for the atmosphere

Convection Most of the heat transport that occurs in the

atmosphere is carried on by convection. Def: The transfer of heat by mass

movement or circulation within a substance Takes place in fluids (oceans, air) where atoms

and molecules are free to move about Pan example:

Warmer water rises, cooler water sinks Uneven heating of water, from the bottom up Water will continue to “turn over”, producing a

convective circulation

Radiation Travels in all directions from its

source Travels through the vacuum of

space, does not need medium like the other two

Radiation is the heat-transfer mechanism by which solar energy reaches our planet

Mechanisms of Heat Transfer

Figure 11.14

Atmospheric Heating Mechanisms of heat transfer

Radiation (electromagnetic radiation) Consists of different wavelengths (distance

from one crest to the next) Gamma (very short waves) X-rays Ultraviolet (UV) Visible

The only portion of the spectrum we can see

White Light as a mixture of colors, each corresponding to a particular wavelength seen through a prism

Infrared (detected as heat) Microwaves and radio waves (longest)

The Electromagnetic Spectrum

Figure 11.15

Atmospheric Heating

Mechanisms of heat transfer Radiation (electromagnetic

radiation) Governed by basic laws

Hotter objects radiate more total energy per unit area than do cooler objects

The hotter the radiating body, the shorter the wavelength of maximum radiation

Objects that are good absorbers of radiation are good emitters as well

Atmospheric Heating Incoming solar radiation

Atmosphere is largely transparent to incoming solar radiation

Atmospheric effects Reflection—Albedo (percent reflected) Scattering Absorption

Most visible radiation reaches the surface

About 50% absorbed at Earth's surface

Average Distribution of Incoming Solar

Radiation

Figure 11.17

Atmospheric Heating Radiation from Earth's surface

Earth re-radiates radiation (terrestrial radiation) at the longer wavelengths

Longer wavelength terrestrial radiation is absorbed by

Carbon dioxide and water vapor Lower atmosphere is heated from

Earth's surface Heating of the atmosphere is

termed the greenhouse effect

Greenhouse effect Approx. 50% of the solar energy that strikes

the top of the atmosphere reaches Earth’s surface and is absorbed

Most of this energy is then reradiated skyward The radiation that it emits has longer wavelengths

than solar radiation (terrestrial radiation) The atmosphere is an efficient absorber of this type

of radiation (85% absorbed) Water vapor and CO2 are the principal absorbing

gases The absorbed terrestrial radiation is then reradiated

back to Earth Atmosphere acts like a real Greenhouse (with

windows open)

Heating of the Atmosphere

Figure 11.19

Global Warming Carbon dioxide in the atmosphere absorbs

some of the radiation emitted by Earth and thus contributes to the greenhouse effect

Changes in content of CO2 could influence air temperature

Rapid growth of industrialization, burning of fossil fuels has added vast quantities of CO2 to the atmosphere

The clearing of forests also contributes substantially. Carbon dioxide is released as vegetation is burned or decays

Consequences of Global Warming? Probable rise in sea level? Shifts in the paths of large-scale storms,

affecting the distribution of precipitation and the occurrence of severe weather

Stronger tropical storms Increases in the frequency and intensity of

heat waves and droughts Gradual environmental shift, imperceptible to

public. Nevertheless will have a strong impact on future economics and thus leading to social and political consequences.

Temperature Measurement

Daily maximum and minimum Other measurements

Daily mean temperature Daily range Monthly mean Annual mean Annual temperature range

Controls of Temperature

Temperature variations Receipt of solar radiation is

the most important control Other important controls

Differential heating of land and water

Land heats more rapidly than water Land gets hotter than water Land cools faster than water Land gets cooler than water

Maritime Influence on Temperature

Figure 11.23

Controls of Temperature

Other important controls Altitude Geographic position Cloud cover Albedo

Clouds Reduce the

Daily Temperatur

e RangeFigure 11.27

World Distribution of Temperature

Temperature maps Isotherm—A line connecting

places of equal temperature Temperatures are adjusted to sea

level January and July are used for

analysis because they represent the temperature extremes

World Distribution of Temperature

Global temperature patterns Temperature decreases poleward

from the tropics Isotherms exhibit a latitudinal

shift with the seasons Warmest and coldest

temperatures occur over land

World Distribution of Temperature

Global temperature patterns In the Southern Hemisphere

Isotherms are straighter Isotherms are more stable

Isotherms show ocean currents Annual temperature range

Small near equator Increases with an increase in

latitude Greatest over continental locations

World Mean Sea-Level Temperatures in

January

Figure 11.28

World Mean Sea-Level Temperatures in July

Figure 11.29

End of Chapter 11