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Atmosphere of Earth

What exactly does the term "atmosphere" imply?


The atmosphere is a thick gaseous envelope that wraps around the world on all sides like a blanket. It is tightly tied to the earth due to its gravitational pull, and it also contains life-giving gases such as oxygen and carbon dioxide.


The majority of the atmosphere is made up of gases, water vapour, and particles.





Gases in Earth's Atmosphere


The earth's atmosphere contains nitrogen (78.08%), oxygen (20.95%), argon (0.93%), carbon dioxide (0.04%), neon, helium, ozone, hydrogen, and other gases.


The ozone gas is observed in extremely small concentrations at a height of 20-25 kilometres and filters the incoming solar energy, preventing ultraviolet rays from reaching the earth.


Carbon dioxide is a greenhouse gas that helps maintain an average temperature of about 15 degrees around the globe.



Water Vapour In Atmosphere


Depending on the region, the amount of water vapour in the atmosphere ranges from 0% to 4% by volume. Water vapour diminishes from the equator to the poles as the temperature drops. The tropical zone (4%) has the highest percentage, whereas polar or desert locations have the lowest rate (1 per cent).


The volume of water vapour decreases as one rise in altitude. All precipitation and condensation events, such as clouds, fogs, dew, rainfall, frost, and snowfall, are caused by the moisture content of the atmosphere.


What is particulate matter, and what effect does it have on the environment?


These are small solid particles in the atmosphere that include dust, salt, pollen, smoke-soot, volcanic ash, and others. It is found in the troposphere or the lowest part of the atmosphere.


The beautiful colours seen at sunrise and sunset are due to the scattering of solar radiation by these particles. The blue colour of the sky is due to dust particles scattering.



STRUCTURE OF THE ATMOSPHERE


Although the precise boundary of the atmosphere is unclear, it is usually assumed to be roughly 1600 kilometres above the earth's surface. The structure of the atmosphere can be split into five tiers based on pressure and air temperature.


  • Troposphere

  • Stratosphere

  • Mesosphere

  • Thermosphere

  • Exosphere


Troposphere


It is the first and the lowest layer of the atmosphere comprising around 75% earth's atmospheric mass. The word troposphere comprises 2 words 'tropos; meaning rotation and 'sphaira' meaning sphere essentially describing the rotation turbulence that affects the flow of gases in this region.


With an altitude of roughly 8 km at the poles and 18 km at the equator, it is positioned between the earth's surface and the upper atmosphere. The thickness is greater at the equator because warm air rises to greater heights.


This zone is also known as the convective region since it is where all convection occurs and stops at Tropopause. It is affected by seasons and jet streams.



What is Tropopause?
The boundary between the troposphere and the stratosphere is called Tropopause. It is the topmost layer of the troposphere lying between the troposphere and the stratosphere. It acts as a transition zone and the temperature remains constant in this layer.

As one ascends this layer, the temperature drops at a rate of 6.5°C/km, reaching - 45°C in the poles and - 80°C at Tropopause over the equator (greater fall in temperature above the equator is because of the greater thickness of troposphere-18 km). The lapse rate refers to how quickly the temperature declines.


The troposphere is characterised by temperature inversion, turbulence, and eddies. In addition, it is the most significant meteorological zone in the entire atmosphere (Almost all the weather phenomena like rainfall, fog and hailstorm etc are confined to this layer).


All cyclones, anticyclones, storms, and precipitation, as well as all water vapours and solid particles, occur in the troposphere, making it the weather zone.



Stratosphere


The stratosphere is the next layer beyond the troposphere, it can be found up to 50 kilometres above the earth's surface. This layer's temperature varies from -51°C to 0°C near Mesosphere. The tempratre remains constant for a short distance before rising with altitude to a temperature of 0°C at 50 kilometres.


This layer is cloud-free for the most part, and weather conditions are ideal for aviation flight. Cirrus clouds can be visible at lower levels at times.


What is Ozonosphere?


It is located between 30 and 60 kilometres above the earth's surface and spans the stratosphere and lower mesosphere. Because of the presence of ozone molecules, this layer reflects harmful UV radiation. The ozonosphere is also known as the chemosphere.


Because there is so much chemical activity in this area. The temperature rises at a rate of 5°C every kilometre through the ozone layer.


Mesosphere


This is an intermediate layer that stretches up to 80 kilometres above the earth's surface and persists beyond the ozone layer. The temperature gradually lowers to -100°C at an altitude of 80 kilometres. This limit is known as mesopause. Meteorites and other alien objects ignite near Mesopause.


Thermosphere


It is a part of the atmosphere beyond the mesopause. As one rise in altitude, the temperature in the thermosphere rapidly rises. It has a length of 80-400 kilometres and also includes the section 'Ionosphere'


What is lonosphere?
This layer is electrically charged and spans 80 to 400 kilometres in length. This layer is characterised by atom ionisation. Due to the electric charge, radio waves radiated from the ground are reflected back to the earth by this layer.

The International Space Station and satellites orbit in this stratum. At this altitude, the atmosphere is very rarefied, with gas molecules separated by hundreds of kilometres.


Aurora Borealis in the North Pole and Aurora Australis in the South Pole are visible in this stratum.






Exosphere

It is the topmost layer of the atmosphere, which extends beyond the ionosphere to a height of roughly 400 kilometres. The air is extremely rarefied, and as the layer proceeds, the temperature increases progressively. On the other hand, no heat is felt.


Light gases like helium and hydrogen travel into space from here.


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