WHAT IS ATMOSPHERE?

The environment or surroundings comprises four major components namely atmosphere, hydrosphere, lithosphere and biosphere. Earth is a sphere with a rough diameter of 8000 miles where the thickness of the atmosphere is roughly around 60 miles. It appears as a thin blue band existing between the earth’s surface and the blackness of space. The atmosphere is in place with the Earth’s surface due to gravity. The composition of the atmosphere is not uniform, with time and location fluid properties constantly changes which are known as the weather.

WHAT IS ATMOSPHERE?

The atmosphere is a thin envelope formed by gases that extends to a height of about 1600km above the surface of the earth reaching the edge of space. Numerous complex chemical, thermodynamic, and fluid dynamics processes take place here. The composition of the atmosphere of Earth is a large percentage of nitrogen (78%), 21% oxygen, and one percent other gases.

LAYERS OF ATMOSPHERE

The layers of atmosphere in order from the surface of the earth i.e. lowest to highest are

TROPOSPHERE

• The most crucial and innermost segment of the atmosphere. The word ‘tropos’ means change.
• It is between 8 to 14.5 kilometres high (5 to 9 miles) thick. The height of the troposphere differs from the equator to the poles being thinnest at the North and South Pole. 
• The air is denser in this lowest layer as the density of the gases decreases with height
• The majority of the weather occurs in this region. In fact, the troposphere constitutes three-quarters of the mass of the entire atmosphere. 
• In context to temperature changes in the troposphere, it decreases with increasing height. On climbing higher, the temperature drops from an average around 62°F (17°C) to -60°F (-51°C) at the tropopause.
• It is the domain of all living organisms including plants and animals and contains water vapour. 

STRATOSPHERE

• • The layer of the stratosphere extends approximately in the range of 12 & 50 km or 7.5 and 31 miles above the surface of the earth.

• The stratosphere is devoid of clouds and weather. The jet planes can reach up to this layer of the atmosphere.

• The stratosphere is the domain of the ozone layer, which is known to provide a shield from ultraviolet radiation (UV rays)
• The higher we ascend in the stratosphere, the hotter is the temperature. This is due to the phenomena of UV rays. “Convection” takes place as there is no upward vertical movement of the gases. The average -60°F at tropopause can reach a maximum of around 5°F at the top of the stratosphere layer.
• The visuals of ‘anvil-shaped’ tops of cumulonimbus clouds give the location of the bottom of this layer.
• It holds 19 per cent of the atmosphere’s gases but minimal water vapour.

MESOSPHERE

• This atmospheric layer extends between the range of 50 & 80 km or 31 and 50 miles above the surface of the earth.
• The separating boundary Stratopause divides the mesosphere from the stratosphere.
• The gases continue to become denser as one descends.
• The temperature increases as one descends, rising to about 5°F (-15°C) near the bottom of this layer. With increasing altitude, the temperature goes progressively lower.
• The stratosphere (next layer down) and the mesosphere are collectively referred to as the middle atmosphere.
• The thick gases in the mesosphere are able to slow down meteors hurtling into the atmosphere, getting burned up leaving fiery trails in the sky. Sounding rockets and rocket-powered aircrafts can reach this layer. 
• The scarce quantity of water vapour prevailing in the upper segment of the mesosphere makes the noctilucent clouds. These make the highest clouds in the atmosphere, can be visualised with naked-eye under certain conditions and times of the day.

THERMOSPHERE 

• The thermosphere extends between about 80 & 700 km or 50 and 440 miles above the surface of the earth.
• This layer is referred to as the upper atmosphere. 
• The gases of the thermosphere become progressively denser on descending towards the earth.
• In this layer, temperatures rise with altitude. It occurs due to two reasons. Firstly, because the molecules present here are less dense and secondly, the molecules absorb high-energy ultraviolet and x-ray radiation from the sun causing a large temperature increase. It can vary to a minimum of -184°f at the bottom and a maximum of 3,600°f near the top.
• Despite the high-temperature conditions, this layer still feels very cold to our skin due to the very thin atmosphere. The distribution of molecules in the thermosphere is not adequate to heat our skin.
• It is devoid of both clouds and water vapour.
• The aurora borealis (northern lights) and aurora australis (southern lights) can sometimes be visualised in this zone.
• The thermosphere is the orbit site for the International Space Station.

EXOSPHERE 

• Referred as the outermost layer and the highest layer of Earth’s atmosphere. its top segment merges with the solar wind. 
• It extends between about 700 and 10,000 kilometres or 440 and 6,200 miles from the top of the thermosphere to above the surface of the earth.
• The bottom of the exosphere has the thermopause located around 375 miles (600 km) above the earth.
• It is the site where atoms and molecules escape into space and most of the earth’s satellites orbit. 
• The molecules in the exosphere have low density therefore it doesn’t exhibit a gas-like behaviour.

• The exosphere is devoid of weather.

• The aurora borealis (northern lights) and aurora australis (southern lights) can sometimes be visualised in the lowest segment of the exosphere.

CONCLUSION

The atmosphere is one of the crucial segments of Earth’s interdependent physical systems. There are five primary and several secondary layers of atmosphere. The five distinct primary layers are the troposphere, stratosphere, mesosphere, thermosphere and exosphere. Each layer is bounded by “pauses”. These transition boundaries see the greatest changes in chemical composition, temperature changes, movement and density of molecules.