thermosphere and beyond


Within the thermosphere is the ionosphere. The ionosphere gets its name from the solar radiation that ionizes 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 density of molecules is so low in the thermosphere that one gas molecule can go about 1 km before it collides with another molecule. Since so little energy is transferred, the air feels very cold (See opening image).


There is no real outer limit to the exosphere, the outermost layer of the atmosphere; the gas molecules finally become so scarce that at some point there are no more. Beyond the atmosphere is the solar wind. The solar wind is made of high-speed particles, mostly protons and electrons, traveling rapidly outward from the Sun.


When massive solar storms cause the Van Allen belts to become overloaded with particles, the result is the most spectacular feature of the ionosphere the nighttime aurora (Figure 1.1). 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. (a) Spectacular light displays are visible as the aurora borealis or northern lights in the Northern Hemisphere. (b) The aurora australis or southern lights encircles Antarctica. What would Earths magnetic field look like if it were painted in colors? It would look like the aurora! This QUEST video looks at the aurora, which provides clues about the solar wind, Earths magnetic field and Earths atmosphere. Click image to the left or use the URL below. URL:



The Van Allen radiation belts are two doughnut-shaped zones of highly charged particles that are located very high the atmosphere in the magnetosphere. The particles originate in solar flares and fly to Earth on the solar wind. Once trapped by Earths magnetic field, they follow along the fields 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.

instructional diagrams

No diagram descriptions associated with this lesson


perhaps the most important feature of the outermost layers of the atmosphere is the low density of the gas particles.

-->  a) true

b) false

this layer bounces off radio waves back to earth.

a) magnetosphere

-->  b) ionosphere

c) mesosphere

d) stratosphere

the aurora borealis is found in this layer.

-->  a) magnetosphere

b) ionosphere

c) mesosphere

d) stratosphere

which gas molecules get energized to make the auroras?

a) oxygen

b) nitrogen

c) hydrogen

-->  d) a & b

at the edge of the outermost layer of the atmosphere, the _, the atmosphere _.

a) ionosphere; merges with outer space

b) ionosphere; ends abruptly

-->  c) exosphere; merges with outer space

d) exosphere; ends abruptly

the solar wind is

a) energized oxygen and nitrogen gas molecules that travel outward from the sun.

-->  b) high speed particles traveling rapidly outward from the sun.

c) the magnetic field of the sun that intersects the orbits of the inner planets.

d) the movement of solar gases from high pressure areas to low pressure areas.

the aurora occur during massive solar storms when the van allen belts are overloaded with particles.

-->  a) true

b) false

how does the ionosphere get its name?

-->  a) solar radiation ionizes gas molecules into positive and negative charges.

b) the magnetic field breaks apart nitrogen and oxygen gas into ions in the atmosphere.

c) solar storms cause the particles in the van allen belts to ionize.

d) ultraviolet radiation breaks apart atmospheric gases into positive and negative charges.

where is the aurora australis found?

a) in the northern hemisphere, near the north pole.

b) encircling the equator.

c) around the tropics of cancer and capricorn.

-->  d) in the southern hemisphere, near the south pole.

what are the van allen belts?

a) a belt-like structure around the tropics of cancer and capricorn where the solar wind strikes.

-->  c) two doughnut-shaped zones of highly charged particles located high in the atmosphere.

d) the polar location where the aurora get their start.

e) where ions travel as electric currents in the magnetosphere.

diagram questions

No diagram questions associated with this lesson