The Earth’s atmosphere is layered and each layer of the atmosphere has its own specific traits. The atmosphere of Earth is divided into four layers as Troposphere, Stratosphere, Mesosphere and Thermosphere. These layers are divided on the basis of temperature.
Weather processes and systems take place in the lower layers of the atmosphere while interesting events such as the beautiful aurora, occur higher in the atmosphere. By understanding the way atmospheric temperature changes with altitude, we can learn a lot about how the atmosphere works.
Structure of the Atmosphere
Unlike the changes in pressure and density, which decreases with altitude, the changes in temperature are irregular. A change in temperature with distance is called a temperature gradient. The Earth’s atmosphere is divided into layers based on the layer’s temperature gradient. The temperature gradient in each layer is determined by the heat source of the layer.
Given here is a temperature gradient diagram of different layers of the atmosphere.
The troposphere is the lowest layer of the atmosphere. We call the lowest part of the troposphere as the boundary layer and the topmost layer is called the tropopause. The air that we breathe exists here and all the weather phenomena such as fog, rainfall and hailstorm occur in this layer. Due to this, the troposphere is thought of as the “zone of weather.” The temperature and the air pressure drop as you go higher in the troposphere.
Why is the troposphere warmer at the base?
Though the sunlight reaches the Earth’s surface from top to bottom, the troposphere is primarily heated at the bottom. This is because the earth surface is much better at absorbing a wide range of solar radiation as compared to the air. When the parcel of warm air moves upwards, it expands. When air expands it cools. Due to this reason, the base of the troposphere is warmer than its base because the air in the surface of the Earth absorbs the sun’s energy, gets heated up and moves upward as a result of which it cools down.
The stratosphere lies above the troposphere and extends up to a height of 50 km. This layer is free of clouds and devoid of any weather-related phenomenon. Due to this aeroplanes fly in the stratosphere for a smooth ride. Stratosphere also houses the ozone layer that protects us from the harmful effect of suns rays.
Why is Stratosphere warmer than the troposphere?
Ozone molecules in stratosphere absorb high energy ultraviolet light from the sun and convert it into heat. Due to this reason, unlike troposphere, the stratosphere gets warmer the higher you go!
The temperature in the mesosphere grows colder with the altitude. This is because there are few gas molecules in the mesosphere to absorb the Sun’s radiation. The only heat source is the stratosphere below. The mesosphere is extremely cold, especially at the top dropping to a temperature as low as -90°C.
Why would an unprotected astronaut’s blood boil in the mesosphere?
An astronaut travelling through mesosphere would experience severe burns from the ultraviolet light of the sun because the ozone layer which provides UV protection is in the stratosphere below. Meteorites burn in this layer on entering the atmosphere from the outer space.
Thermosphere and Beyond
The density of molecules in the thermosphere is very low. One gas molecule can go about a distance of 1 km without colliding another molecule. Because so little energy is transferred, the air feels very cold. Satellites are found orbiting in the upper part of the thermosphere.
Ionosphere lies within the thermosphere. 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. These freed electrons travel within the ionosphere as electric currents. Due to these free ions, the ionosphere has many interesting characteristics. The aurora, the Northern Lights and Southern Lights, occur in the Earth’s ionosphere.
Exosphere is the final frontier of the Earth’s gaseous envelope. There is no clear cut distinction between the Earth’s atmosphere and the outer space. The air in the exosphere is constantly but gradually leaking out of the Earth’s atmosphere into outer space.
Visualising Layers of Atmosphere
How to remember the layers of the atmosphere?
Atmospheric Layers Mnemonic
Mnemonic device for the layers of Earth’s atmosphere:
That Snake Must Think: I’m Evil
The first alphabet of each word corresponds to the layer of Earth’s atmosphere starting from the Earth’s surface. These are troposphere, stratosphere, mesosphere, thermosphere. The thermosphere is divided into the ionosphere (northern lights) and exosphere (satellites)
Frequently Asked Questions on The Layers of the Atmosphere
Which is the hottest layer of the atmosphere?
The thermosphere is the hottest layer of the atmosphere.
Which is the coldest layer of the atmosphere?
Mesosphere is the hottest layer of the atmosphere.
Which is the outermost part of the Earth’s atmosphere?
Exosphere is the outermost part of the Earth’s Atmosphere.
Which factor determines a new layer in the atmosphere?
Temperature shift determines a new layer in the atmosphere.
In which layer of the atmosphere is ozone found?
The ozone layer is found in the stratosphere.
In which layer of the atmosphere do planes fly?
Planes fly in the stratosphere for a smooth ride due to less turbulence.
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