The Earth’s atmosphere is what allows us to breathe and stay alive on our planet.
It is a mixture of gases that surrounds our planet as well as shielding us from ultraviolet (UV) radiation that comes from the sun, too much UV radiation is harmful to us.
We learn in school that the atmosphere is made from several different layers that all serve unique functions. In total there are five layers of the atmosphere and one of the outermost layers is called the thermosphere.
In this article, we are going to talk about the thermosphere and talk about its particular characteristics.
What Is The Thermosphere?
The thermosphere refers to one of the five layers of the Earth’s atmosphere, it lies between the exosphere and the mesosphere.
Therefore, it is considered the last layer of the atmosphere that resembles the layers closest to the Earth’s surface.
This layer can be found just above the mesosphere which ends at 85km high and extends to around 600km high.
Is It Hot Or Cold?
As you might already know “thermo” means heat, as the temperatures can reach up to 4,000℉ in this layer it was justly named the thermosphere.
When the thermosphere receives more radiation from the Sun during more active periods, this causes the thermosphere to heat up and expand. As a result, the height of the top end of the thermosphere varies.
What Is The Thermosphere Made Of?
All the layers of the atmosphere contain gases, the thermosphere is made up of atomic oxygen (O), atomic nitrogen (N), and helium (He).
This layer is completely cloudless and free of water vapor due to its composition.
This layer of the atmosphere can be separated into two further layers:
The ionosphere is the ionized innermost layer of the thermosphere. Energy from the Sun electrically charges this layer, which can lead to the phenomenon of the Aurora Borealis via the charged particles.
The exosphere in turn is the outermost layer of the thermosphere, it is at this point the atmosphere thins out and merges into outer space.
This layer is approximately 700 to 10,000 km above the Earth’s surface. At the top of this layer, you can find solar winds.
What Is The Atmosphere Like?
Overall, the density of the thermosphere is very low, but the density of the mesopause is even lower than this and is often thought to resemble the density seen in outer space.
This is unsurprising as air density decreases as altitude increases.
If someone were to be out in the thermosphere, they would feel very cold as there is a very thin atmosphere. The air is so thin that it can act as a vacuum.
As particles are many km apart, they cannot conduct enough energy to provide heat to our skin.
Circulation In The Thermosphere
Similarly to the Earth’s surface, the thermosphere has weather and a climate that can be altered depending on various factors.
Atmospheric tides, gravity waves, and planetary waves can also impact the winds in this layer of the atmosphere.
Solar winds are mainly driven by the variation between the absorption of solar EUV and UV radiation, which heats and expands the thermosphere creating horizontal pressure gradients.
Winds in this layer of the atmosphere can reach up to 1 kilometer per second depending on the level of disturbance in conditions (see also ‘What Is The Orographic Effect? How Does It Change The Weather?‘). Satellites get dragged by the winds in this level, which can impact their life span.
Another weather feature found in this layer of the atmosphere is the thermospheric storm.
During these storms, magnetospheric energy is the major driving force in thermospheric heating. This causes the thermosphere to heat up, expand, and circulate.
These storms create a denser atmosphere and have the capacity to drag the low-orbiting satellites and even cause a loss of tracking knowledge. However, this depends on the strength of the storm.
Are There Any Clouds In The Thermosphere?
The thermosphere is still considered to be part of the Earth’s surface, so it does actually contain clouds!
As we mentioned before, the space between the mesosphere and the thermosphere is called the mesopause.
At these altitudes, polar mesospheric clouds can form as high as 85km above the Earth’s surface.
Water vapor freezes forming clouds of ice crystals, at night these high clouds are sometimes illuminated by the setting sun and create a ‘shiny’ appearance (see also ‘How Do Glaciers Form?’).
These types of clouds are usually only seen at certain times of the year and by those in aircraft, or those who have higher viewpoints such as astronauts.
How Important Is The Thermosphere?
The thermosphere is important as it absorbs the Sun’s ultraviolet and infrared radiation as it passes through, sort of acting like a sponge.
When humans are exposed to too much UV light, it can have harmful impacts on our health.
There are three different types of UV rays, and not all of them make it through to us on the Earth’s surface due to the barriers that the atmosphere creates.
UVA rays do reach the Earth’s surface and when it comes into contact with human skin they can cause premature aging and eye damage. Also see ‘Can You Tan on a Cloudy Day? Understanding the Science Behind Tanning and Weather‘.
This is why we are always told to wear sunscreen and sunglasses when we’re outside. UVA rays have also been found to increase the risk of developing skin cancer.
The atmosphere helps to shield us from the majority of UVB rays. However, there are certain factors that may influence this such as latitude, altitude, and time of year amongst others.
These rays are just as damaging as UVAs, causing us to get sunburnt without protection, skin cancer, and skin aging. UVBs can also cause a burn on the cornea which can lead to a temporary loss of sight.
As UVC rays are absorbed by the Earth’s atmosphere, there are minimal to no harmful effects felt by humans.
Armed with this information, it’s evident that the thermosphere along with the other layers of the Earth’s atmosphere is important for helping to disperse and scatter the UV rays that come from the Sun.
The majority of skin cancers are caused by the exposure of skin to UV light. This damages the DNA of the skin cells. Overall, UVB is the biggest cause for concern and is thought to be the main cause of skin cancer overall.
How Does The Aurora Borealis Work?
If you’ve not heard of this, you might know the phenomenon as the Northern lights. This colorful light display is usually found in the northern hemisphere close to the Earth’s magnetic poles.
When electrically charged particles are emitted from the Sun and occasionally become trapped by the Earth’s magnetic field.
If this occurs, these particles are drawn toward the north and south poles, which is why this phenomenon occurs here.
The particles collide with atoms and molecules in the Earth’s upper atmosphere such as the thermosphere, causing them to heat up.
This produces tiny flashes of brightly colored light that present themselves across the sky (see also ‘Why The Sky Is Blue… A Closer Look‘).
If you’ve ever witnessed this phenomenon, you may notice there are ‘lines’ and ‘waves’ of light in the sky. These shapes indicate the lines of force of the Earth’s magnetic field.
The aurora isn’t limited to just the thermosphere, although the lowest part that is most visible to humans may be around 80 miles from the Earth’s surface, the far end of the display could be several thousand miles above this.
Climate Change And The Thermosphere
Climate change has given cause for concern for many of the Earth’s atmospheric layers and more recently, this applies to the upper layers of the atmosphere too.
Research conducted by Cnosse recently found evidence that the rising carbon dioxide levels from Earth are the main driver in the long-term cooling of the thermosphere.
The Earth’s magnetic field has also been found to play an important role in the thermospheric climate change happening at the poles.
NASA satellites have also found evidence that the upper atmosphere may be contracting due to human-driven climate change.
This causes satellite drag and may also increase the chance of space junk hanging around in a low orbit.
The full extent of the changes to the upper atmosphere is still being researched and is not yet fully understood.
There is the potential to disrupt radio communications in the stratosphere and cause an increase in the concentration of water vapor.
Facts About The Thermosphere
Here are some of the interesting key facts about the thermosphere that might give you a better understanding of this layer of the atmosphere:
- The thermosphere is where you can find the International Space Station and other low Earth orbit satellites. The Space Station can be found between 200 to 240 miles from the Earth’s surface.
- Although the thermosphere can reach hot temperatures, there aren’t enough gas molecules to actually transfer the heat to other areas, so you’d feel quite chilly if you were floating there.
- There aren’t enough molecules for sound waves to travel through the thermosphere.
- The thermosphere extends from around 90km to between 500-1000km above Earth.
- A lot of the X-ray and UV radiation that comes to the Earth from the Sun is absorbed in this layer.
- Non-hydrometeorological phenomena such as the aurora borealis can be seen in the thermosphere.
- The space between the thermosphere and the exosphere is called the ‘thermopause’.
- The space between the thermosphere and the mesosphere is called the ‘mesopause’.
- As the thermosphere extends so far from the Earth’s surface, some consider the layer to be a part of outer space rather than within the Earth’s atmosphere.
- This layer is helpful with radio communication as shortwave radio waves can bounce off the Kennelly-Heaviside layer.
The Bottom Line
The thermosphere is one of the outermost layers of the Earth’s atmosphere and is often considered to be a part of outer space as a result.
As with all other layers of the atmosphere, the thermosphere has its own unique characteristics and functions that help keep life on the surface working as usual.
Frequently Asked Questions
What Is Important About The Thermosphere?
Arguably the most important thing about the thermosphere is the fact that it absorbs some of the most harmful rays emitted by the sun.
These include x-rays and ultraviolet rays that we talked about above, overexposure to these can lead to loss of vision and skin cancer.
How Thick Is The Thermosphere?
The thermosphere is in the middle ground in terms of thickness, the layer spans around 513km.
This means that it’s much thicker than the lower layers closer to the surface of the Earth but much thinner than the exosphere.
Check out this video if you would like to know more about the thermosphere.