Physical Geography - Version 1 Unit 6 Earth’s Atmosphere

Elm Figure At in the Ancient Pine Forest . The White Mountains , California . Image by Jeremy is used under a license . UNIT EARTH ATMOSPHERE Goals Objectives of this unit Understand the significance of the atmosphere . Describe the composition of the atmospheric gasses . Explain the major layers ofthe atmosphere and their importance . Analyze the relationships between energy , temperature , and heat . Identify and explore the Earth solar budget and identify the values of albedo . Describe how heat is transferred around the planet . GEOGRAPHY

THE SIGNIFICANCE OF THE ATMOSPHERE Earth atmosphere is a thin blanket of gases and tiny particles called air . We are most aware of air when it moves and creates wind . All living things need some of the gases in the air for life support . Without an atmosphere , Earth would likely be just another lifeless rock . atmosphere , along with the abundant liquid water at Earth surface , is the keys to our unique place in the solar system . Much of what makes Earth exceptional depends on the atmosphere . Let consider some of the reasons we are lucky to have an atmosphere . Indispensable for Life on Earth Without the atmosphere , Earth would look a lot more like the Moon . Atmospheric gases , especially carbon dioxide ( and oxygen ( 02 ) are extremely important for living organisms . How does the atmosphere make life possible ?

How does life alter the atmosphere ?

In photosynthesis , plants use and create 02 . Photosynthesis is responsible for nearly all of the oxygen currently found in the atmosphere . By creating oxygen and food , plants have made an environment that is favorable for animals . In respiration , animals use oxygen to convert sugar into food energy they can use . Plants also go through respiration and consume some of the sugars they produce . Along with the oceans , the atmosphere keeps Earth temperatures within an acceptable range . Greenhouse gases trap heat in the atmosphere so they help to moderate global temperatures . Without an atmosphere with greenhouse gases , Earth temperatures would be frigid at night and scorching during the day . Important greenhouse gases include carbon dioxide , methane , water vapor , and ozone . ATMOSPHERIC GASSES Nitrogen and oxygen together make up 99 of the planet atmosphere . The rest of the gases are minor components but are sometimes very important . Humidity is the amount of water vapor in the air . Humidity varies from place to place and season to season . This fact is obvious if you compare a summer day in Atlanta , Georgia , where humidity is high , with a winter day in Phoenix , Arizona , where humidity is low . When the air is very humid , it feels heavy or sticky . Dry air usually feels more comfortable . Higher humidity is found around the equatorial regions because air temperatures are higher and warm air can hold more moisture than cooler air . Of course , humidity is lower near the Polar Regions because the air temperature is lower . GEOGRAPHY

Some of what are in the atmosphere is not gas . Particles of dust , soil , fecal matter , metals , salt , smoke , ash , and other solids make up a small percentage of the atmosphere . Particles provide starting points ( or nuclei ) for water vapor to condense on and form raindrops . Table Showing Atmospheric Gasses as a Percent by Volume Gas Symbol Volume ( Nitrogen Oxygen 02 Argon A 09340 Carbon Dioxide Neon Ne Helium He Hydrogen Atmospheric Pressure Density The atmosphere has different properties at different elevations above sea level or altitudes . The air density ( the number of molecules in a given volume ) decreases with increasing altitude . This is why people who climb tall mountains , such as . Everest , have to set up camp at different elevations to let their bodies get used to the decreased air . Why does air density decrease with altitude ?

Gravity pulls the gas molecules towards Earth center . The pull of gravity is stronger closer to the center at sea level . Air is denser at sea level where the gravitational pull is greater . Gases at sea level are also compressed by the weight ofthe atmosphere above them . The force of the air weighing down over a unit of area is known as its atmospheric pressure . The reason why we are not crushed by this weight is that the molecules inside our bodies are pushing outward to compensate . Atmospheric pressure is felt from all directions , not just from above . GEOGRAPHY

Atmospheric Pressure Altitude Atmospheric Pressure ( 10 100 90 80 70 SO 40 30 for 15 deg and humidity ' 10 2000 4000 6000 8000 10000 Figure Diagram Explaining Pressure Changes with Altitude . Image has been designated to the public domain under a Universal Public Domain Dedication . At higher altitudes , the atmospheric pressure is lower , and the air is less dense than at higher altitudes . If your ears have ever popped , you have experienced a change in air pressure . Gas molecules are found inside and outside your ears . When you change altitude quickly , like when an airplane is descending , your inner ear keeps the density of molecules at the original altitude . Eventually , the air molecules inside your ear suddenly move through a small tube in your ear to equalize the pressure . This sudden rush of air is felt as a popping sensation . Although the density of the atmosphere changes with altitude , the composition stays the same with altitude , with one exception . In the ozone layer , at about 20 to 40 above the surface , there is a greater concentration of ozone molecules than in other portions ofthe atmosphere . LAYERS OF THE ATMOSPHERE The atmosphere is layered , corresponding with how the atmosphere temperature changes with altitude . By understanding the way temperature changes with altitude , we can learn a lot about how the atmosphere works . While weather takes place in the lower atmosphere , interesting things , such as the beautiful aurora , happen higher in the atmosphere . Why does warm air rise ?

Gas molecules can move freely and if they are uncontained , as they are in the atmosphere , they can take up more or less space . GEOGRAPHY When gas molecules are cool , they are sluggish and do not take up as much space . With the same number of molecules in less space , both air density and air pressure are higher . When gas molecules are warm , they move vigorously and take up more space . Air density and air pressure are lower . Warmer , lighter air is more buoyant than the cooler air above it , so it rises . The cooler air then sinks , because it is denser than the air beneath it . The property that changes most strikingly with altitude is air temperature . Unlike the change in pressure and density , which decreases with altitude , changes in air temperature are not regular . A change in temperature with distance is called a temperature gradient . The atmosphere is divided into layers based on how the temperature in that layer changes with altitude , the temperature gradient . The temperature gradient of each layer is different . In some layers , temperature increases with altitude , and others , it decreases . The temperature gradient in each layer is determined by the heat source of the layer . Most ofthe important processes of the atmosphere take place in the lowest two layers the troposphere and the stratosphere . Mesosphere Figure Layers of Earth Atmosphere Temperature Gradient . Image is in the public domain . GEOGRAPHY

Troposphere The temperature of the troposphere is highest near the surface of the Earth and decreases with altitude . On average , the temperature gradient ofthe troposphere is per ( per ) of altitude . What is the source of heat for the troposphere ?

Earth surface is a major source of heat for the troposphere , although nearly all of that heat comes from the Sun . Rock , soil , and water on Earth absorb the Sun light and radiate it back into the atmosphere as heat . The temperature is also higher near the surface because of the greater density of gases . The higher gravity causes the temperature to rise . Notice that in the troposphere warmer air is beneath cooler air . What do you think the consequence of this is ?

This condition is unstable . The warm air near the surface rises and cool air higher in the troposphere sinks . The air in the troposphere does a lot of mixing . This mixing causes the temperature gradient to vary with time and place . The rising and sinking of air in the troposphere mean that all of the planet weather takes place in the troposphere . Sometimes there is a temperature inversion , air temperature in the troposphere increases with altitude and warm air sits over cold air . are very stable and may last for several days or even weeks . They form Overland at night or in winter when the ground is cold . The cold ground cools the air that sits above it , making this low layer of air denser than the air above it . Near the coast where cold seawater cools the air above it . When that denser air moves inland , it slides beneath the warmer air over the land . Stratosphere Ash and gas from a large volcanic eruption may burst into the stratosphere , the layer above the troposphere . Once in the stratosphere , it remains suspended there for many years because there is so little mixing between the two layers . Pilots like to fly in the lower portions ofthe stratosphere because there is little air turbulence . In the stratosphere , temperature increases with altitude . What is the heat source for the stratosphere ?

The direct heat source for the stratosphere is the Sun . The air in the stratosphere is stable because warmer , less dense air sits over cooler , denser air . As a result , there is little mixing of air within the layer . The ozone layer is found within the stratosphere between 15 to 30 ( to 19 miles ) altitudes . The thickness of the ozone layer varies by the season and also by latitude . The ozone layer is extremely important because ozone gas in the stratosphere absorbs most of the Sun harmful ultraviolet ( UV ) radiation . Because of this , the ozone layer protects life on Earth . The UV light penetrates cells and damages DNA , leading to cell death ( which we know as a bad sunburn ) Organisms on Earth are not adapted to heavy UV exposure , which GEOGRAPHY

kills or damages them . Without the ozone layer to reflect and radiation , the most complex life on Earth would not survive long . Mesosphere Temperatures in the mesosphere decrease with altitude . Because there are few gas molecules in the mesosphere to absorb the Sun radiation , the heat source is the stratosphere below . The mesosphere is extremely cold , especially at its top , about ( The air in the mesosphere has extremely low density ofthe mass of the atmosphere is below the mesosphere . As a result , air pressure is very low . A person traveling through the mesosphere would experience severe burns from ultraviolet light since the ozone layer which provides UV protection is in the stratosphere below . There would be almost no oxygen for breathing . Stranger yet , an unprotected traveler blood would boil at normal body temperature because the pressure is so low . The density of molecules is so low in the that one gas molecule can go about before it collides with another molecule . Since so little energy is transferred , the air feels very cold . Within the is the ionosphere . The ionosphere gets its name from the solar radiation that gas molecules to create a positively charged ion and one or more negatively charged electrons . The freed electrons travel within the ionosphere as electric currents . Because of the free ions , the ionosphere has many interesting characteristics . At night , radio waves bounce off the ionosphere and back to Earth . This is why you can often pick up an AM radio station far from its source at night . The Van Allen radiation belts are two zones of highly charged particles that are located beyond the atmosphere in the magnetosphere . The particles originate in solar flares and fly to Earth on the solar wind . Once trapped by Earth magnetic field , they follow along the field magnetic lines of force . These lines extend from above the equator to the North Pole and also to the South Pole then return to the equator . When massive solar storms cause the Van Allen belts to become overloaded with particles , the result is the most spectacular feature of the ionosphere or the nighttime aurora . The particles spiral along magnetic field lines toward the poles . The charged particles energize oxygen and nitrogen gas molecules , causing them to light up . Each gas emits a particular color of light . GEOGRAPHY

ATMOSPHERIC HEAT , ENERGY MOTION Energy travels through space or material . This is obvious when you stand near a fire and feel its warmth or when you pick up the handle of a metal pot even though the handle is not sitting directly on the hot stove . Invisible energy waves can travel through air , glass , and even the vacuum of outer space . These waves have electrical and magnetic properties , so they are called electromagnetic waves . The transfer of energy from one object to another through electromagnetic waves is known as radiation . Different wavelengths of energy create different types of electromagnetic waves . The wavelengths humans can see are known as visible These wavelengths appear to us as the colors of the rainbow . What objects can you think of that radiate visible light ?

Two include the Sun and a light bulb . The longest wavelengths of visible light appear red . Infrared wavelengths are longer than visible red . Snakes can see infrared energy . We feel infrared energy as heat . Wavelengths that are shorter than violet are called ultraviolet . Can you think of some objects that appear to radiate visible light , but do not ?

The moon and the planets do not emit light of their own they reflect the light of the Sun . Reflection is when light ( or another wave ) bounces back from a surface . Albedo is a measure of how well a surface reflects light . A surface with high albedo reflects a large percentage of light . A has a high albedo . One important fact to remember is that energy can not be created or destroyed , it can only be changed from one form to another . This is such a fundamental fact of nature that it is a law the law of conservation of energy . In photosynthesis , for example , plants convert solar energy into chemical energy that they can use . They do not create new energy . When energy is transformed , some nearly always becomes heat . Heat transfers between materials easily , from warmer objects to cooler ones . If no more heat is added , eventually all ofthe material will reach the same temperature . Temperature Temperature is a measure of how fast the atoms in a material are vibrating . particles vibrate faster than temperature particles . Rapidly vibrating atoms smash together , which generates heat . As a material cools down , the atoms vibrate more slowly and collide less frequently . As a result , they emit less heat . What is the difference between heat and temperature ?

Temperature measures how fast a material atoms are vibrating . GEOGRAPHY Heat measures the material total energy . Which has higher heat , and which has a higher temperature a candle flame or a bathtub full of hot water ?

The flame has a higher temperature , but less heat , because the hot region is very small . The bathtub has a lower temperature but contains much more heat because it has many more vibrating atoms . The bathtub has greater total energy . Heat Heat is taken in or released when an object changes state , or changes from a gas to a liquid , or a liquid to a solid . This heat is called latent heat . When a substance changes state , latent heat is released or absorbed . A substance that is changing its state of matter does not change temperature . All ofthe energy that is released or absorbed goes toward changing the state . For example , imagine a pot of boiling water on a stove burner that water is at ( If you increase the temperature of the burner , more heat enters the water . The water remains at its boiling temperature , but the additional energy goes into changing the water from liquid to gas . With more heat , the water evaporates more rapidly . When water changes from a liquid to a gas it takes in heat . Since evaporation takes in heat , this is called evaporative cooling . Evaporative cooling is an inexpensive way to cool homes in hot , dry areas . Substances also differ in their specific heat , the amount of energy needed to raise the temperature of one gram of the material by ( Water has a very high specific heat , which means it takes a lot of energy to change the temperature of the water . Let compare a puddle and asphalt , for example . If you are walking barefoot on a sunny day , which would you rather walk across , the shallow puddle , or an asphalt parking lot ?

Because of its high specific heat , the water stays cooler than the asphalt , even though it receives the same amount of solar radiation . Atmospheric Pressures Winds A few basic principles go a long way toward explaining how and why air moves Warm air rising creates a zone at the ground . Air from the surrounding area is sucked into the space left by the rising air . Air flows horizontally at top of the troposphere horizontal flow is called advection . The air cools until it descends . When the air reaches the ground , it creates a zone . Air flowing from areas of high pressure to low pressure creates winds . Warm air can hold more moisture than cold air . Air moving at the bases of the three major convection cells in each hemisphere north and south of the equator creates the global wind belts . GEOGRAPHY

Within the troposphere are convection cells . Air that moves horizontally between and zones makes wind . The greater the pressure difference between the pressure zones the faster the wind flow . Convection in the atmosphere creates the planet weather . When warm air rises and cools in a zone , it may not be able to hold all the water it contains as vapor . Some water vapor may condense to form clouds or precipitation . When cool air descends , it warms . Since it can then hold more moisture , the descending air will evaporate water on the ground . Air moving between large and systems create the global wind belts that profoundly affect regional climate . Smaller pressure systems create localized winds that affect the weather and climate of a local area . Clear Skies Cloudy Skies Descending Air Diverging wind Converging wind High Fe Figure Diagram Explaining Bath Law High Pressure in the Northern Hemisphere . Image by OER team is used under a license . Pressure Local Winds Local winds result from air moving between small low and systems . and cells are created by a variety of conditions . Some local winds have very important effects on the weather and climate of some regions . Land Sea Breezes Since water has a very high specific heat , it maintains its temperature well . As water is heated and cools more slowly than land . Ifthere is a large temperature difference between the surface of the sea ( or a large lake ) and the land next to it , and regions form . This creates local winds . Sea breezes blow from the cooler ocean over the warmer land in summer . Where is the zone and where is the zone ?

Sea breezes blow at about 10 to 20 ( to 12 miles ) per hour and lower air temperature much as to ( to ) GEOGRAPHY warm air cool sea breeze sea cooler night land cooler sea warmer Figure Land Sea Breezes . Image by Encyclopedia used appropriately under Encyclopedia terms of use . Monsoonal Winds Monsoon winds are versions of land and sea breezes they blow from the sea onto the land in summer and from the land onto the sea in winter . Monsoon winds occur where very hot summer lands are next to the sea . Thunderstorms are common during monsoons . The most important monsoon in the world occurs each year over the Indian subcontinent . More than two billion residents of India and southeastern Asia depend on monsoon rains for their drinking and irrigation water . Back in the days of sailing ships , seasonal shifts in the monsoon winds carried goods back and forth between India and Africa . GEOGRAPHY

Mountain Valley Breezes Temperature differences between mountains and valleys create mountain and valley breezes . During the day , air on mountain slopes is heated more than air at the same elevation over an adjacent valley . As the day progresses , warm air rises and draws the cool air up from the valley , creating a valley breeze . At night the mountain slopes cool more quickly than the nearby valley , which causes a mountain breeze to flow downhill . 04 Figure Mountain Valley Breezes . Image is in the public domain . Katabatic Winds Katabatic winds move up and down slopes , but they are stronger mountain and valley breezes . Katabatic winds form over a highland area , like a high plateau . The plateau is usually surrounded on almost all sides by mountains . In winter , the plateau grows cold . The air above the plateau grows cold and sinks from the plateau through gaps in the mountains . Wind speeds depend on the difference in air pressure over the plateau and the surroundings . Katabatic winds form over many continental areas . Extremely cold katabatic winds blow over Antarctica and . GEOGRAPHY

Air is cooled by ice surface KATABATIC WIND causes to descend . ANTARCTIC ICE SHEET I ' SOUTHERN OCEAN SEA BED Figure Katabatic Winds . Image is used under a Alike International license . Chinook Winds Chinook winds develop when air is forced up over a mountain range . This takes place , for example , when the westerly winds bring air from the Pacific Ocean over the Sierra Nevada Mountains in California . As the relatively warm , moist air rises over the windward side of the mountains , it cools and contracts . If the air is humid , it may form clouds and drop rain or snow . When the air sinks on the leeward side of the mountains , it forms a zone . The windward side of a mountain range is the side that receives the wind the leeward side is the side where air sinks . The descending air warms and creates strong , dry winds . Chinook winds can raise temperatures more than ( in an hour and they rapidly decrease humidity . If precipitation falls as the air rises over the mountains , the air will be dry as it sinks on the leeward side . This dry , sinking air causes a rain shadow effect , which creates many of the world deserts . Dry Air Advances 55 Rain Shadow Warm Moist Air Figure . Image by Anders has been released in the public domain . GEOGRAPHY

Santa Ana Winds Santa Ana winds are created in the late fall and winter when the Great Basin east ofthe Sierra Nevada cools , creating a zone . The forces the winds downhill and in a clockwise direction in the Northern Hemisphere ( because ofthe effect ) The air pressure rises , so temperature rises and humidity falls . The winds blow across the Southwestern deserts and then race downhill and westward toward the ocean . Air is forced through canyons cutting the San Gabriel and San mountains . The Santa Ana winds often arrive at the end of California long summer drought season . The hot , dry winds dry out the landscape even more . If a fire starts , it can spread quickly , causing devastation . Figure The Santa Ana Winds Note the Direction Being Eastward . Image by NASA is in the public domain . Desert Winds High summer temperatures on the desert create high winds , which are often associated with monsoon storms . Desert winds pick up dust because there is not as much vegetation to hold down the dirt and sand . A haboob forms in the on the front of a thunderstorm , as the ground becomes so hot that the air above it heats and rises . Air flows into the low pressure and begins to spin . Dust devils are small and , but they may cause damage . GEOGRAPHY

Figure Haboob in Texas in 1935 . Image is in the public domain . GLOBAL ATMOSPHERIC Because more solar energy hits the equator , the air warms and forms a zone . At the top of the troposphere , half moves toward the North Pole and half toward the South Pole . As it moves along the top of the troposphere it cools . The cool air is dense and when it reaches a zone it sinks to the ground . The air is sucked back toward the low pressure at the equator . This describes the convection cells north and south ofthe equator . If the Earth did not rotate , there would be one convection cell in the Northern Hemisphere and one in the south with the rising air at the equator and the sinking air at each pole . But because the planet does rotate , the situation is more complicated . The planet rotation means that the effect must be taken into account . Let look at atmospheric circulation in the Northern Hemisphere as a result of the effect . Air rises at the equator , but as it moves toward the pole at the top of the troposphere , it deflects to the right . Remember that it just appears to deflect to the right because the ground beneath it moves . At about latitude , the air from the equator meets air flowing toward the equator from the higher latitudes . This air is cool because it has come from higher latitudes . Both batches of air descend , creating a pressure zone . Once on the ground , the air returns to the equator . This convection cell is called the Cell and is found between and GEOGRAPHY

Tropopause Subtropical Jet Equator Figure The Three Cell Model Circulation . Image by Anthony Flores is used under a license . There are two more convection cells in the Northern Hemisphere . The cell is between and to . This cell shares its southern , descending side with the cell to its south . Its northern rising limb is shared with the Polar cell located between to and the North Pole , where cold air descends . There are three mirror image circulation cells in the Southern Hemisphere . In that hemisphere , the Effect makes objects appear to deflect to the left . Ultimately , because there are three convection cells in the Northern Hemisphere and are repeated in the Southern Hemisphere , the model to understand these patterns is called the model . Global Wind Patterns Global winds blow in belts encircling the planet . The global wind belts are enormous , and the winds are relatively steady . These winds are the result of air movement at the bottom of the major atmospheric circulation cells , where the air moves horizontally from high to low pressure . Technology today allows anyone to see global wind patterns in , such as the Earth Wind Mag . Take a look at the Earth Wind Map and determine what patterns you can see occurring in the atmosphere in . Are systems rotating counterclockwise in the Northern Hemisphere ?

Are systems rotating clockwise in the Northern Hemisphere ?

Can you see the global wind patterns over the Atlantic and Pacific Oceans ?

Also , notice how the winds flow faster over water than over continents because of land friction . GEOGRAPHY In the cell , air should move north to south , but it is deflected to the right by the effect . So , the air blows from northeast to southwest . This belt is the trade winds , because at the time of sailing ships they were good for trade . Pin It ! Map So , what do wind patterns look like today ?

Check out the Earth Wind Map link below to find out ! use in arctic zone Tropopause in temperate cell cell convergence zone on cell cell Polar cell ' Figure Global Winds Atmospheric Circulation Model . Image is used under a Alike license . In the cell , air should move south to north , but the winds blow from the southwest . This belt is the westerly winds or . Why do you think a flight across the United States from San Francisco to New York City takes less time than the reverse trip ?

GEOGRAPHY Finally , in the Polar cell , the winds travel from the northeast and are called the polar . The wind belts are named for the directions from which the winds come . The westerly winds , for example , blow from west to east . These names hold for the winds in the wind belts of the Southern Hemisphere as well . The Polar Fronts Jet Streams The polar front is the junction between the and Polar cells . At this zone , relatively warm , moist air of the Cell runs into relatively cold , dry air of the Polar cell . The weather where these two meet is extremely variable , typical of much of North America and Europe . The stream is found high up in the atmosphere where the two cells come together . A jet stream is a river of air at the boundary between the troposphere and the stratosphere . Jet streams form where there is a large temperature difference between two air masses . Subtropical jet Polar Jet North Pole Figure Global Circulation Pattern with Jet Streams . Image is used under an Alike International license . This explains why the stream is the world most powerful . Jet streams move as the angle of the Sun in the sky migrates north and south . The stream , known as the jet stream , moves south in the winter and north in the summer . GEOGRAPHY

The atmosphere is a mixture of nitrogen ( 78 ) oxygen ( 21 ) and other gases ( that surround Earth . High above the planet , the atmosphere becomes thinner until it gradually reaches space . It is divided into four layers , based on temperature , and two based on density . Most of the weather and clouds are found in the first layer . The atmosphere is an important part of what makes Earth livable . It blocks some of the dangerous rays from reaching Earth . It traps heat , making Earth a comfortable temperature . And the oxygen within our atmosphere is essential for life . Global and local winds are identified based on which direction the air comes from . Because of rising warm air at specific lines of latitude , warm air can mix with cool air , driving weather . GEOGRAPHY