The thin shell of gas around our planet that we call our atmosphere is divided into several layers. While the pressure falls with increasing altitude, the temperature is more dynamic, alternately decreasing and increasing with altitude.
There are six layers of the atmosphere around the Earth:
- Troposphere [surface to 10-18 km]
- Stratosphere [11 to 50 km]
- Mesosphere [40-50 to 80-90 km]
- Thermosphere [80-90 to 800 km]
- Exosphere [800 to 10000 km]
The troposphere is the lowest layer of Earth’s atmosphere. All life on our planet is affected by the changes that happen in this layer. And also, all the weather changes take place in the troposphere. It starts from the ground/surface (meaning as at the sea level) of our planet and expands up to 12 km up in the sky.
Actually, the depth of the troposphere layer varies between 8 km to nearly 20 km, depending on where you live. It is the deepest above the equator, and thicker above the poles.
This is the layer when we talk about the levels of oxygen, the one layer that contains the most of this gas every living thing on this planet needs. The higher we go in this layer of the atmosphere, the thinner the air gets. This basically means that humans would have a hard time breathing than in the lowest parts of the troposphere.
This gives you an idea of why it becomes so challenging when we climb high mountain peaks and climbers take extra oxygen if needed.
Above the top of the troposphere and further, up into the sky, the layer known as the stratosphere is placed. This layer goes up from 11 km to around 50 km above the Earth’s surface. In this layer, the temperature normally rises as you go further up, and it has something to do with the ozone layer that is found inside the stratosphere.
The ozone layer, however, serves a vital role in the protection of our planet, as the molecules of ozone prevent ultraviolet light (known as UV) from the Sun to hit our planet without stopping. The UV light is not technically stopped in this layer, but the conversion from ultraviolet light to heat occurs there. That is why holes in the ozone layer (known as the ozone hole) are dangerous for us.
Another very important feature in the stratosphere is known as the polar vortex. This is an enormous, three-dimensional ring of winds that surrounds the North and South poles. These winds are located about 20 to 50 km above the Earth’s surface. And the polar vortex often plays an important role in the winter weather across the high and mid-latitudes.
The mesosphere is the third and middle layer, being halfway up our atmosphere layers when we reach this part. The mesosphere goes up from 40/50 km to 80 or 90 km above the surface of our planet, and the temperatures here behave as they do in the troposphere. So the higher you go, the colder it gets.
The mesosphere has very low oxygen levels, so it would be impossible to breathe there. This layer of the atmosphere also has the lowest temperature of all layers. It could get as cold as low as near -90° C.
Red sprites, a known type of transient luminous event (TLE), are also found in the mesosphere layer. They are different from the more familiar lightning that takes place in the troposphere, but they occur high above the thunderstorm tops and can be photographed from the Earth’s surface or from space (e.g. International Space Station).
The Thermosphere layer is located between 100 and 800 km above the Earth’s surface level. And the interesting fact is, that its name ‘Thermo’ has got its naming because high temperatures are found in this layer. The Thermosphere is under constant attack from the X-rays and UV radiation coming from the Sun and the space around Earth. This is also the reason why the temperatures in this layer can even reach up to 2000° C.
The Northern Lights (also known as Aurora Borealis) and Southern Lights (known as Aurora Australis) mostly occur in the thermosphere. Charged particles (e.g. electrons and protons) from space collide with atoms and molecules in the thermosphere at high latitudes.
These collisions exciting them into higher energy states. Those atoms and molecules shed this excess energy by emitting photons of light, which we see as colorful auroral displays.
The final and the highest layer is known as the Exosphere. Unlike other lower and better-known layers, which are mostly distinguishable from one another, it is quite hard to know how far the exosphere is from the surface of the planet.
Somewhere it is around 100.000 km, but it can expand up to 190.000 km above sea level. The air here is very thin in this layer, and the conditions here are more similar to the ones we find when we leave the Earth’s atmosphere entirely. Basically similar to outer space.
Virtually all the weather happens in the troposphere and thunderstorm clouds are (mostly) confined to the troposphere. Therefore, all phenomena discussed here take place in the troposphere unless specifically stated otherwise.
- The edge of space – the Karman line – is at 100 km height, within the thermosphere
- The highest ever balloon ride and parachute jump were made by Alan Eustace in 2014: he rose up to 41.419 m and made a safe parachute jump.
- Meteors appear in the thermosphere and mesosphere, usually between 130 and 70 km. Some have been detected as high as almost 170 km, and some penetrate do less than 20 km above the ground, well within the stratosphere.
Now that we have seen the structure of our atmosphere, let us take a look at the part of the atmosphere thunderstorms (and we) live in.
Let us take a closer look at the troposphere. The pressure at sea level is approximately 1 bar or 1000 millibar (mbar or hPa). If you manage to get below sea level, without diving beneath the sea surface, the pressure is higher. For example, on the coast of the Dead Sea in Israel, at 430 m below sea level, the air pressure is just above 1060 millibar.
As you go higher in the troposphere the pressure drops. This happens because the higher you are, the less the atmosphere or air column there is above you, pushing down on you. At the altitude of the peak of Europe’s highest mountain, Mt Blanc (4807 m), the air pressure is only about 430 mbar.
That is less than half that at sea level. On top of Mt Everest (8848 m), the air pressure is only about 340 mbar. And at aircraft cruising altitude of about 12 km, it is only about 200 mbar, only 1/5 that at sea level.
The troposphere cools with altitude, i.e. the higher you go, the colder the air is. On average, the air is cooler by about 0.7 °C for every 100 m higher you go. So, while it may be a pleasant 25 °C or more on the surface, it is -50 °C or below an aircraft cruising altitude at 10 km altitude or more.
The gradual change of the temperature with height is called a vertical temperature gradient or temperature lapse rate.
Recap: In the troposphere, the temperature drops with height. While it is usually relatively warm near the surface it is very cold high up in the troposphere. The rate at which the temperature drops is called the vertical temperature gradient.
Now we will take a look at what drives the formation of thunderstorms.