1. Earth’s protective bubble
LOOKING AT THE EARTH’S ATMOSPHERE
This spectacular image of sunset on the Indian Ocean was taken by astronauts aboard the International Space Station (ISS). The image presents an edge-on, or limb view, of the Earth’s atmosphere as seen from orbit. The Earth’s curvature is visible along the horizon line, or limb, that extends across the image from center left to lower right. Above the darkened surface of the Earth, a brilliant sequence of colors roughly denotes several layers of the atmosphere.
Deep oranges and yellows appear in the troposphere, which extends from the Earth’s surface to 6–20 km high. This layer contains over 80 percent of the mass of the atmosphere and almost all of the water vapor, clouds, and precipitation. Several dark cloud layers are visible within this layer. Variations in the colors are due mainly to varying concentrations of either clouds or aerosols (airborne particles or droplets).
The pink to white region above the clouds appears to be the stratosphere; this atmospheric layer generally has little or no clouds and extends up to approximately 50 km above the Earth’s surface. Above the stratosphere, blue layers mark the upper atmosphere (including the mesosphere, thermosphere, ionosphere, and exosphere) as it gradually fades into the blackness of outer space. - picture caption from Wikipedia
NASA accessed via Wikipedia

2. What’s so special?
Earth is surrounded by a blanket of air called the atmosphere
Extends near or over 600 kilometers from Earth’s surface
Held by Earth’s gravitational pull
Composed of many different gases
Separated into several different layers
Protects us from outer space
Blocks out dangerous rays (UV) from the sun
Quite transparent to visible light
The atmosphere just “fades away” into space with increasing altitude
The depth of the atmosphere is quite shallow compared to the size of the Earth (radius of Earth = 6370km)

3. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
A PROFILE OF THE atmosphere reveals it can be divided into distinct layers Each layer can be defined by the gases that comprises it or temperature variation or electrical properties Separating the layers is a boundary or “pause” where the greatest changes properties occur
Ionosphere
Heterosphere
Homosphere
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
The upper atmosphere is consider to be the thermosphere and above; starts at 85km that’s 52 miles (very high up!)
The lower atmosphere is consider to be the troposphere, where we live
The atmosphere can be defined a few different ways:
Composition (in yellow)
Temperature (in red)
Electrical properties (in purple)
First lets look at the composition of the atmosphere …
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
The source of this material is Windows to the Universe, at at the National Earth Science Teachers Association (NESTA) < Windows to the Universe® is a registered trademark. All Rights Reserved

4. Mixing it up Homosphere Heterosphere The air we breathe is very
lower atmosphere
Heterosphere
upper atmosphere
The air we breathe is very
well mixed
The air is comprised of
78%: Nitrogen (N2)
21%: Oxygen (O2)
other 1%: “trace” gases
Argon (Ar)
Carbon Dioxide (CO2)
Ozone (O3)
Water (H2O)
… and more
The air in the upper atmosphere is very different from the air we breathe
The air is not well mixed
Atoms get sorted by atomic weight
Hydrogen and Helium can sometimes escape gravity
HOMOSPHERE
Air is well mixed meaning a sample of air from the your house will be comprised of the same elements as a sample of air from Mt. Everest.
99% of the atmosphere is comprised of Nitrogen and Oxygen
Why is oxygen important? It is used by all living things and is essential for respiration (breathing)
Trace gases only present in minute amounts but are very important to life on Earth
Carbon dioxide and ozone can have large impacts on atmospheric processes
Plants use carbon dioxide to make oxygen during photosynthesis
Carbon dioxide also acts as a blanket to prevent heat from escaping to outer space
Ozone filters out the sun’s harmful UV rays
Water vapor varies in composition (almost non existent over desert regions to 4% over oceans)
Water is very important to weather since it exists in all three phases (gaseous, liquid, and solid) and absorbs energy radiating from the Earth
Other trace gases include Neon, Helium, Krypton, Hydrogen, Xenon, Methane, Nitrous Oxide, Sulfur Dioxide, and Chlorofluorocarbons (CFCs)
HETEROSPHERE
A sample of air from the lower region of the upper atmosphere will not consist of the same atoms and molecules as a same from a higher region
Gravity is pulling down the heavier elements
The heavier elements like nitrogen and oxygen at the same temperature are moving slower than lighter atoms like hydrogen and helium (velocity is proportional to 1/mass). The lighter atoms have less of a gravitational force acting upon them so they can travel further away from earths gravitational pull and sometimes can escape it.
Wikipedia | Public Domain

5. Troposphere
Surface ~ 15km
The lower atmosphere The Weather zone Almost all weather occurs in this layer height of the troposphere varies from the equator (15km) to the poles (9km) transport of energy heats this layer As you go up … (increase in altitude) Pressure decreases density of gases decreases Temperature decreases uniformly A transition zone known as the tropopause is the boundary between the troposphere and stratosphere … all dry (almost)!
The troposphere begins at the Earth’s surface and extends from 9 to 15km
It is the layer we reside in.
All weather events like precipitation, storms, and clouds (except the few seen in the stratosphere and mesosphere) occur in the troposphere
Why do think this is? Nearly all of the water vapor and dust particles are found in this layer to form clouds.
Height of the troposphere varies because of latitude, season, and whether its day or night.
The sun warms the ground or ocean which radiates the heat right above the surface. Remember warm air rises and as it does it expands and cools. The air at the troposphere is cool. The cooler air aloft sinks down and as it does it heats up. This keeps things “stirred up” … convection
The warmer surface temperatures at the equator and mixing helps push the height of the troposphere.
The average height of the troposphere is 12 km
The air becomes “thinner”. There would not be enough oxygen for us to survive. This is why sometimes mountain climbers need oxygen to breathe like on Mount Everest
At higher elevations there are fewer air molecules over a given surface area compared to lower levels which is why pressure is less.
The temperature decreases at a rate 6.5 C/km. This is known as the environmental lapse rate.
At the tropopause temperature remains constant with height and becomes almost completely dry.
Fun Fact about the tropopause: No vertical mixing is the reason for the anvil shaped tops of thunderstorm clouds (cumulonimbus)
Kathryn Haughn
The source of this material is Windows to the Universe, at at the National Earth Science Teachers Association (NESTA) < Windows to the Universe® is a registered trademark. All Rights Reserved

6. Stratosphere
15km ~ 50km
stable layer (ideal for jet planes Ozone layer is in this layer Let it Linger (CFC’s, Volcanic ash, aerosols) weather balloons As you go up … Pressure decreases Air is dry and less dense temperature increases (-52°c ~ -3°c) 99% of the atmosphere is located in the troposphere and stratosphere! A transition zone known as the stratopause is the boundary between the stratosphere and mesosphere … what pressure?
The stratosphere starts just above the tropopause and extends to 50 km
Many jet planes fly in the lower stratosphere because it is very stable.
There is not a lot of mixing because the warmer air is located above cooler air which prevents convection
Large concentrations of ozone are found at 25 km (the “ozone layer”) which absorbs and scatters much of the UV radiation emitted by the sun. Without the ozone layer life could not exist on Earth.
Due to a lack of convection materials that get into the stratosphere can stay there for a long time and can have some major impacts. Like CFC’s which are ozone destroying chemicals or large volcanic eruptions and major meteorite impacts produce aerosol particles that can sometimes can alter our climate or even rockets eject exhaust gases and we are not sure about the consequences.
Weather balloons or high-altitude balloons (unmanned) are released from the surface into the stratosphere, generally reaching (18 to 37 km). This is known as “near space” because it is the area of the atmosphere where there is very little air but is not high enough for satellite observations. Balloons are launched twice a day at various weather service stations around the world. The balloon carries instruments that sends back information on various atmospheric conditions like pressure, temperature, humidity and wind speed. The balloon is filled with either hydrogen or helium.
The atmosphere is getting thinner and has very little water vapor present.
When temperature increases with height this is called an INVERSION
Increasing temperature in this layer is caused by ozone … As UV is being absorbed by ozone, heat is released, warming the layer.
99% of atmosphere is located in the troposphere and stratosphere so that means the remaining 1% is found in the other three layers!
At the stratopause temperature remains constant with height
The atmospheric pressure is about 1000 times thinner at the top of the stratosphere than it is at sea level
NASA
The source of this material is Windows to the Universe, at at the National Earth Science Teachers Association (NESTA) < Windows to the Universe® is a registered trademark. All Rights Reserved

7. Mesosphere
50KM ~ 85 KM
The cold layer noctilucent clouds meteors burn up in this layer Not easy to study As you go up … Pressure decreases density of gases continues to decrease Temperature decreases (-3°c ~ -90°c) A transition zone known as the mesopause is the boundary between the mesosphere and thermosphere … Coldest place on earth!
Why is it so cold? (Approximately )~1% of the atmospheric ozone is found in this layer. Therefore there is very little ozone to absorb solar radiation
Noctilucent clouds can be seen occasionally during the summer time over the polar regions. This proves that even this high up in the atmosphere there still is trace amounts of (frozen) water vapor. Where does it come from? SEE MEET ME IN THE MESOSPHERE
Meteors entering the atmosphere burn up in this layer leaving trails in the night sky
Scientists know less about the mesosphere than any other layer because it hard to make measurements and study. Weather balloons and jet planes can’t fly high enough and satellites can’t orbit low enough. Sometimes rockets are launched to make measurements but the flights are short and they do go into orbit.
The gases continue to get thinner and thinner with increasing height
Temperature decreases with height
NASA
The source of this material is Windows to the Universe, at at the National Earth Science Teachers Association (NESTA) < Windows to the Universe® is a registered trademark. All Rights Reserved

8. Thermosphere
85km ~ 600km
The upper atmosphere HOT! HOT! Hot! not much around (Molecules that is) X-Ray and UV radiation absorbed Space shuttles and international space station orbit in this layer sensitive to solar activity aurora overlaps and shares space with ionosphere As you go up … Pressure decreases density of molecules is extremely lowTemperature increases (-90°c ~ 2000°c)
Temperatures can range from 500°C to as high as 2000°C!!
The high temperatures are caused by the absorption of intense solar radiation by oxygen (O2)
The amount of energy being absorbed is very small … So why the extreme temperatures?
Since density of the atoms and molecules in the thermosphere is extremely low any absorption of solar energy causes a large increase in temperature in this layer
The air is so thin that a molecule can travel 1 km before hitting another molecule … At the surface this happens less than a millionth of a centimeter!!
This is why we wouldn’t be able to detect the extreme heat in this layer because we depend on the constant bombardment of molecules to detect temperature.
Gases tend to sort themselves out depending on weight. Heavier elements like nitrogen and oxygen have a great gravitational pull than lighter elements like hydrogen and helium so they do not extend up to high altitudes.
Energetic UV and X-ray radiation from the sun can also break apart molecules
Atomic oxygen (O), atomic nitrogen (N) and helium (He) are the main components of the thermosphere’s air.
Solar activity has a strong influence on the temperature in the thermosphere.
The daytime it is typically 200°C hotter than at night.
During solar maximum the temperature is about 500°C hotter.
Aurora borealis (Northern lights) and Aurora australis (Southern lights)
Aurora is produced by the solar wind disturbing the magnetosphere.
High energy particles within the magnetic field lines are ejected into the upper atmosphere. These particles collide and excite the atmospheric atoms and molecules. When atmospheric gases are excited they emit visible radiation causing the sky the glow. Nitrogen emits red or violet light and oxygen emits green light.
Ionosphere is the region of the atmosphere that is filled with charged particles (we will talk more about this region a little later)
Temperatures increase sharply in the lower thermosphere (below 300km) and then level off and increase steadily with height.
NASA
The source of this material is Windows to the Universe, at at the National Earth Science Teachers Association (NESTA) < Windows to the Universe® is a registered trademark. All Rights Reserved

9. Exosphere
600+ km
The escape zone extends until it merges with space upper limit of our atmosphere comprised of mainly hydrogen and helium satellites orbit earth in this layer
The region where moving air molecules and atoms shoot off into space
They escape earth’s gravitational pull
The upper limit is not well defined
Why do you think the exosphere is comprised of hydrogen and helium?
(Hint: think where these elements are located on the periodic table)
They are the lightest gases. All other atoms and molecules are too heavy
Hydrogen and Helium are present at extremely low densities
NASA
The source of this material is Windows to the Universe, at at the National Earth Science Teachers Association (NESTA) < Windows to the Universe® is a registered trademark. All Rights Reserved

10. THE ELECTRIFIED REGION SHOWS YET ANOTHER WAY LAYERS OF THE ATMOSPHERE CAN BE DEFINED
Windows to the Universe® ( © 2010, National Earth Science Teachers Association.

11. IONOSPHERE (60km – top of atmosphere)
AN ELECTRIFIED REGION (NOT REALLY A LAYER ITSELF) WITHIN THE UPPER ATMOSPHERE
EXISTENCE IS DUE TO THE SUN’S RADITATION
THE DENSITY CHANGES FROM DAYTIME TO
NIGHTTIME
AM RADIO COMMUNICATION RELIES ON THE IONOSPHERE
CONSISTS OF IONS AND FREE ELECTRONS
IONS ARE ATOMS AND MOLECULES THAT HAVE LOST OR
GAINED ELECTRON(S)
STARTS AT ABOUT 60KM AND EXTENDS
TO THE TOP OF THE ATMOSPHERE
DIVIDED INTO 3 LAYERS;
THE D, E, AND F LAYERS
Ionosphere begins in the upper mesosphere (60km) and extends to the top of the atmosphere
The bulk of the ionosphere is in what layer? Thermosphere
Atoms or molecules that lose an electron become positively charged. This happens when they cannot absorb all of the energy being transferred to them during collisions with high energy particles (short wavelengths) like the sun. This is called ionization. When the sun is active more and more ionization happens.
Just think the sun’s energy is so strong that it breaks apart atoms and molecules so there are electrons and ions floating around
**The breakdown of the layers is based on what wavelength of solar radiation is absorbed (most frequently) in that region**
MIT Haystack
NOAA

12. THE D LAYER LOWEST LAYER ABSORBS GAMMA AND X-RAYS
REFLECTS AM RADIO WAVES BACK TO EARTH
AT NIGHT THE LAYER DISAPPEARS (GRADUALLY) AT NIGHT
WHAT HAPPENS TO THE AM RADIO WAVES THEN?
The D layer does not have a definite starting and ending point but it includes ionization that occurs below 90km
At night (since the D layer disappears) AM radio waves are able to travel higher into the ionosphere. The waves repeatedly bounce from the ionosphere to the Earth’s surface. This is why AM radio waves are able to travel hundreds of miles at night.
Test it out … Tonight find the farthest AM station broadcasting. Where is it? Tomorrow morning or day try to find that same station. Can you?
FACT: FM radio waves are shorter in wavelength than AM radio waves so they are able to travel through the ionosphere without being reflected.
NOAA

13. more on the ionosphere THE E LAYER PEAKS AT 105KM ABSORBS X-RAYS
THE F LAYER
The Millstone Hill Observatory is an atmospheric research facility owned and operated by MIT.
The instrument used by scientists to study the ionosphere is a large incoherent scatter radar (pictured). There is a large steerable antenna which has a diameter of 150ft (pictured in the background) and a zenith antenna (88° elevation) which has a diameter of 220ft (pictured in the foreground). The radar is capable of measuring a variety of properties of the ionosphere including temperatures, ion concentrations, and space weather effects.
HIGHEST LAYER
UP TO 600KM or MORE
ABSORBS EXTREME UV
MIT Haystack
Kathryn Haughn

14. Credit: John Emmert/NRL