THE ATMOSPHERE

C O M P O S I T I O N ,S T R U C T U R E ,

& T E M P E R AT U R E

COMPONENTS OF THE ATMOSPHERE

Nitrogen and Oxygen• the most plentiful components

of air • significant to life on Earth• has minor importance in

affecting weather phenomena Carbon Dioxide• present in only minute amounts

(0.037%)• an important constituent of air• an efficient absorber of energy

emitted by Earth• influences the heating of the

atmosphereVariable Components:Aerosols, Water Vapor, Ozone

WATER VAPOR

• Amount varies from 0-4% by volume• the source of all clouds and precipitation• has the ability to absorb heat given off by Earth as well as some solar energy

AEROSOLS• solid and liquid particles suspended in air for considerable amount of time• Origin:

– Sea salts from breaking waves– fine soil blown into air– smoke and soot from fires– pollen and microorganisms blown by wind– ash and dust from volcanic eruptions

• act as surfaces on which water vapor can condense (an important function in the formation of fog and clouds)

• Can absorb, reflect, and scatter incoming solar radiation• Contributes to an optical phenomenon we have all observed– the varied

hues of red and orange sunrise and sunset

OZONE• O3, not the same as the oxygen we breathe• concentrated in the stratosphere (altitude between

10-50 km)• absorbs UV radiation emitted by the sun (UV is also

needed to form Ozone)• If ozone did no filter a great deal of the UV radiation,

and if the UV rays reached the surface of the Earth undiminished, our planet would be uninhabitable for most life.• Anything that reduces the amount of Ozone in the

atmosphere could affect the well-being of life on earth

OZONE DEPLETION: A GLOBAL ISSUE• Over the past 60 years, people have placed the ozone layer in

jeopardy by POLLUTING the atmosphere.• Most significant pollutants:

– chlorofluorocarbons (CFCs)Uses of CFCs – coolants for air-condition and refrigeration equipment, cleaning solvents for electronic components, propellants for aerosol sprays, and the production of certain plastic foams

• CFS are practically inert in the lower atmosphere so these gases escapes to the ozone layer, where sunlight separates the chemicals into their constituents atoms. CHLORINE ATOMS break up some of the ozone particles.

OZONE DEPLETION: A GLOBAL ISSUE• A decrease in ozone concentration permits more

harmful wavelengths to reach Earth’s surface.• Threats of exposure to UV radiation:

– increased risk of skin cancer– can impair the human immune system– promote cataracts– reduced vision leading to blindness

• In 2009 the ozone hole covered an area about the size of North America. (NASA)

Ozone Distribution in the Southern Hemisphere

ozone hole

SOURCES AND TYPES OF AIR POLLUTION• Air pollutants – airborne particles and gases that occur in concentrations that

endanger the health and well-being of organisms or disrupt the orderly functioning of the environment.

• Primary Pollutants – emitted directly from identifiable sources (industrial processes, electrical generation, solid waste disposal, and transportation)

– Carbon monoxide (CO)– nitrogen oxides (NO2)– sulfur dioxides (SOx)– volatile organic compounds (VOCs)– particulate matters (PM)

• Secondary Pollutants – forms in the atmosphere when reactions take place among primary pollutants (ex: SO2 forming sulfuric acid, VOCs forming photochemical smog)

CONCEPT CHECK

• What are the 2 major components of clean, dry air?• Why are water vapor and aerosols important

constituents of Earth’s atmosphere?• What is Ozone? Why is it important to life on Earth?

VERTICAL STRUCTURE OF THE ATMOSPHERE

• Where does the atmosphere end and the outer space begin?

There is no sharp boundary; the atmosphere rapidly thins as you travel away from Earth, until there are too few gas molecules to detect.

ATMOSPHERIC VARIATION WITH ALTITUDE

• The rate of pressure decrease with an increase in altitude is not constant.• Pressure decreases

rapidly near Earth’s surface and more gradually at greater heights.

THERMAL STRUCTURE OF THE ATMOSPHERE

Radiosondes supply data on vertical changes in temperature, pressure, and humidity.

A lightweight package of instruments, the radiosonde, is carried aloft by a small weather balloon.

The orange object beneath the balloon is a small parachute that deploys after the balloon bursts.

(Photo by Michael Burnett/Photo Researchers, Inc.)

TROPOSPHERE• The bottom layer in which we live• temperature decreases with an

increase in altitude• the chief focus of meteorologists,

because it is in this layer that essentially all important weather phenomena occur• Thickness varies with latitude and

the season• atmospheric properties like

temperature and humidity are readily transferred by large-scale turbulence and mixing

Environmental Lapse Rate• The temperature decrease

in the troposphere• average value is 6.5°C per

kilometer• can be highly variable, and

must be regularly measured

Radiosoundes attached to a balloon transmit data (ex: vertical changes in pressure, wind, and humidity) by radio as it ascends through the atmosphere

Tropopose• the outer boundary of the

troposphere

STRATOSPHERE• the temperature remains

constant to a height of about 20 kilometers (12 miles) and then begins a gradual increase that continues until the stratopause, at a height of nearly 50 kilometers (30 miles) above Earth’s surface• Temperatures increase in the

stratosphere because it is in this layer that the atmosphere’s ozone is concentrated

MESOSPHERE• Temperatures again decrease with

height until, at the mesopause, more than 80 kilometers (50 miles) above the surface

• accessibility is difficult• one of the least explored regions

of the atmosphere• cannot be reached by the highest

research balloons nor is it accessible to the lowest orbiting satellites

THERMOSPHERE• extends outward from the

mesopause and has no well-defined upper limit• a layer that contains only a

tiny fraction of the atmosphere’s mass• temperatures again increase,

owing to the absorption of very short-wave, high-energy solar radiation by atoms of oxygen and nitrogen• Temperatures (or the average

speed at which molecules move ) rise to extremely high values of more than 1000°C

CONCEPT CHECK

•

EARTH-SUN RELATIONSHIPS• nearly all of the energy that drives Earth’s variable

weather and climate comes from the Sun• It is the unequal heating of Earth that creates winds and

drives the ocean’s currents• These movements, in turn, transport heat from the

tropics toward the poles in an unending attempt to balance energy inequalities. • If the Sun were “turned off,” global winds and ocean

currents would quickly cease. • the variations in solar heating are caused by the motions

of Earth relative to the Sun and by variations in Earth’s land–sea surface

EARTH’S MOTION

Rotation• Earth’s spin about an axis• produces the daily cycle of

day and night• Circle of Illumination – line

separating the dark half of the Earth from the lighted half

Revolution• Earth’s orbital movement

around the Sun• Earth travels an elliptical

orbit around the Sun at 113, 000 km per hour

SEASONS• depends on the

length of daylight and altitude of the Sun

Changes in the Sun’s angle cause variations in the amount of solar energy reaching Earth’s surface.

The higher the angle, the more intense the solar radiation

ENERGY, HEAT, AND TEMPERATURE• The universe is made up of a combination of matter and energy.• Energy – the capacity to do work; thermal

– Types of energy: chemical, nuclear, radiant (light), and gravitational energy– Kinetic energy - energy of motion

• Heat – a term that is commonly used synonymously with thermal energy.

– refers to the quantity of energy present• Temperature – is related to the average kinetic energy of a

material’s atoms or molecules– refers to the intensity, that is, the degree of “hotness”

• Heat is the energy that flows because of temperature differences. In all situations, heat is transferred from warmer to cooler objects.

MECHANISMS OF HEAT TRANSFER• Conduction - the transfer of heat through matter by

molecular activity; Energy is transferred through collisions from one molecule to another, with the heat flowing from the higher temperature to the lower temperature

• Convection - the transfer of heat by mass movement or circulation within a substance; It takes place in fluids (e.g., liquids like the ocean and gases like air) where the atoms and molecules are free to move about.

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

FATE OF INCOMING SOLAR RADIATION

Reflection and Earth’s Albedo• Energy is returned to

space from Earth in two ways: reflection and emission of radiant energy.

• About 30% of the solar energy reaching the outer atmosphere is reflected back to space.

• The fraction of the total radiation that is reflected by a surface is called its albedo.

Radiation may be absorbed, transmitted, or redirected (reflected or scattered).

Scattering• scattering accounts for

the brightness and even the blue color of the daytime sky

• half of the solar radiation that is absorbed at Earth’s surface arrives as diffused (scattered) light

Absorption• Nitrogen, the most abundant constituent in the atmosphere, is a poor absorber

of all types of incoming radiation. • Oxygen and ozone are efficient absorbers of ultraviolet radiation. Oxygen

removes most of the shorter ultraviolet radiation high in the atmosphere, and ozone absorbs most of the remaining ultraviolet rays in the stratosphere.

• The absorption of UV radiation in the stratosphere accounts for the high temperatures experienced there

• For the atmosphere as a whole, none of the gases are effective absorbers of visible radiation. This explains why most visible radiation reaches Earth’s surface and why we say that the atmosphere is transparent to incoming solar radiation

FATE OF INCOMING SOLAR RADIATIONRadiation may be absorbed, transmitted, or redirected (reflected or

scattered).

THE GREENHOUSE EFFECT

AIR TEMPERATURE DATA• At a weather station, the temperature is

read on a regular basis from instruments mounted in an instrument shelter

• The shelter protects the instruments from direct sunlight and allows a free flow of air.

• In addition to a standard mercury thermometer, the shelter is likely to contain a thermograph to continuously record temperature and a set of maximum–minimum thermometers.

• Max.-Min. Thermometers record the highest and lowest temperatures during a measurement period, usually 24 hours

The daily maximum and minimum temperatures are the bases for many of the temperature data compiled by meteorologists:

1. By adding the maximum and minimum temperatures and then dividing by two, the daily mean temperature is calculated. 2. The daily range of temperature is computed by finding the difference between the maximum and minimum temperatures for a given day. 3. The monthly mean is calculated by adding together the daily means for each day of the month and dividing by the number of days in the month. 4. The annual mean is an average of the 12 monthly means. 5. The annual temperature range is computed by finding the difference between the highest and lowest monthly means.

WHY TEMPERATURES VARYThe Controls of Temperature:• Land and Water• Altitude• Geographic Position• Cloud Cover and Albedo

WEATHER & CLIMATE

•Weather – refers to the state of the atmosphere at a given time and place; constantly changing, sometimes from hour to hour and at other times from day to day

•Climate - climate is the sum of all statistical weather information that helps describe a place or region

BASIC ELEMENTS OF WEATHER AND CLIMATE

• (1) air temperature, • (2) humidity, • (3) type and amount of cloudiness, • (4) type and amount of precipitation, • (5) air pressure, and • (6) the speed and direction of the wind

- quantities or properties that are measured regularly

END OF CHAPTER 16