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 Climate 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 Seasons 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 Changing length of daylight 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 Temperature Range Figure 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