Layers of The Atmosphere
Most of the atmosphere above our heads is totally invisible to us. And yet, if we could view it somehow, we’d actually see a great deal of complexity. That’s because the Earth’s atmosphere is made up of 5 distinct layers! As we’ll see, each of these layers has unique properties.
Before we dive in, we should make a brief note about a term we’ll use. That is the pause. The boundary between each atmospheric layer is a ‘pause’. Each has a specific name for their layer. For example, the top of the troposphere is called the tropopause.
The troposphere is the first layer of the atmosphere. It’s also the one we live in! It extends from the Earth’s surface to about 12 miles in the sky.
We can’t really understate the importance of the troposphere. For one, it contains most of the air and water vapor in our atmosphere. This is despite the fact that it’s the thinnest layer. Similarly, its high water vapor and air content create interesting effects on Earth. The vapor contributes to what’s called the greenhouse effect. This means it traps the Sun’s heat close to our planet.
A cartoon showing how the greenhouse effect works. Put simply, heat comes in, but not all of it goes out.
One major impact of this is weather! Weather is the result of how water vapor and heat move around the Earth. As a result, almost all weather happens in the troposphere.
Another impact of the greenhouse effect is that it keeps our planet nice and warm. If we couldn’t trap heat, the dark side of the Earth would be extremely cold!
The layer above the troposphere is the stratosphere. The stratosphere is a much less dense layer, containing only 19% of the Earth’s gas. Although, it’s also thicker than the troposphere. It spans from the tropopause to about 31 miles up. The most notable feature of the stratosphere is the ozone layer. This is a thin part of the stratosphere which contains a molecule called ozone. Ozone is really good at absorbing the Sun’s UV radiation. Without it, much more of this harmful radiation would reach us.
One more fact about the stratosphere is that, above the ozone layer, its temperature actually increases. The top of the stratosphere is the hottest part of it! This is because the ozone layer generates a lot of heat. This heat then rises to warm the stratosphere.
Normally as we move upwards, things get colder. The opposite is true of the stratosphere.
Our next atmospheric layer is the mesosphere. It extends from the stratopause to around 58 miles high. Notably, temperatures start to decrease again throughout the mesosphere. The mesopause is actually the coldest region in our atmosphere!
Another notable feature of the mesosphere is its airglow. Airglow is a faint glow that we can see in the night sky. It’s always there – but brighter lights tend to block it out. Next time you’re out at night, try and see if you can spot it.
The greenish light in the background is airglow. It’s pretty, but hard to see. Photo Credit: Christos Doudoulakis
The layer above the mesosphere is the thermosphere. The thermosphere is where things start to get pretty strange. For starters, the layer spans almost 300 miles (from 80 to 375 miles high). It’s also incredibly hot as temperatures can reach up to 4,500 degrees Fahrenheit! This is because the air in thermosphere absorbs lots of solar radiation.
We should also note that the thermosphere is where aurorae are made! They are a result of all the radiation it absorbs.
The Northern Lights, a beautiful creation of our thermosphere.
The last layer of the atmosphere is the exosphere. The exosphere starts at the thermopause but doesn’t really have a clear end. Instead, it just thins out until it becomes as empty as outer space.
Similar to the thermosphere, the exosphere can get pretty hot. Although, its temperature varies greatly between night and day. At night, it gets freezing cold, while during the day it can be several thousand degrees Fahrenheit.
Lapse Rate and Inversions
One final thing we should discuss is what’s called lapse rate. Lapse rate is the rate at which temperatures change as we move upwards. We’ve seen that this isn’t constant. In the troposphere, it’s colder as we go up. In the stratosphere, it gets hotter.
Whenever we switch between raising and lowering temperature, we call it an inversion. For example, the lapse rate inverts between the troposphere and stratosphere.
Other Great Resources:
Ducksters on the Make-up of Our Atmosphere: https://www.ducksters.com/science/atmosphere.php
Shorter Guide to the Layers of the Atmosphere: https://eo.ucar.edu/kids/sky/air6.htm
(Video) Layers of the Atmosphere – The Dr. Binocs Show: https://www.youtube.com/watch?v=5sg9sCOXFIk