Earth’s Atmosphere – Mesosphere

The atmosphere has six layers, each having its characteristics. These layers are Troposphere, Stratosphere, Mesosphere, Thermosphere & Exosphere, starting from ground level. These layers are like a protective blanket around the Earth to create a habitat for human beings by maintaining an adequate climate and protection  from the ill effects of unwanted solar radiations, meteorites, and comets.

What is Mesosphere?

Talking about Mesosphere, the word comes from the Greek word ‘mesossphaira’ which means middle layer, and thus it is called the middle atmosphere as it lies in the middle of all the layers.

Being at a high altitude, the air present in the mesosphere is very thin and not breathable for us humans. The atmosphere of the layer comprises Oxygen, nitrogen, and Carbon dioxide, they are all mingled together, and are not in the form of layers as per their respective masses, as we see in the lower part of the atmosphere. 

Also, the density of air is much less in the mesosphere as compared to the lower sphere of the Atmosphere. 99.9 % of the mass of the atmosphere is below the mesosphere. The atmospheric pressure at the mesopause (top of mesosphere) is only 0.01 millibars which is only 1/100000th of the Earth’s surface pressure.

Characteristics of the Mesosphere

• The mesosphere lies between the stratosphere and thermosphere layer of the atmosphere.
• The mesosphere is approximately 37 km thick and does not have any clear start or endpoints. It is located at an altitude stretching from 50 km to 100 km away from the surface of the Earth.
• The mesosphere’s exact boundaries depend on the latitude of the location one is observing it from: it is higher at the tropics and lower at the poles. The boundaries also vary according to the seasons: it is higher in winter and lowers in summer.
• This sphere is sometimes known to be a “near space’ area, being the higher boundary spanning up to 100 km.
• At the top of this mesosphere area, the temperature ranges between -130 degrees Celsius to -150 degrees Celsius, being known as ‘Mesopause’. The temperature decreases as one goes further higher. As the layer absorbs the radiation from the sun, heat decreases, emission of carbon-dioxide cools increasingly.
• The mesopause area is said to be the coldest part of the atmosphere. It becomes so cold in this area that it freezes water vapour into ice clouds. These clouds are called noctilucent clouds or polar mesospheric clouds and are blue-white and are more visible at sunset from the Earth’s pole.

Importance of Mesosphere

The ozone concentration decreases in the mesosphere as compared to the stratosphere, which means there is less absorption of Ultraviolet light in this layer of the atmosphere. This happens because Shortwave, elevated radiation coming from the sun is soaked up by particles of the “O2” and “N”.

One of the most important traits of this sphere is that it provides protection to the planet, and us, from meteorites and comets through destruction of the same prior to their reaching the Earth’s surface. Meteors and asteroids pass easily through the top two-sphere (outer layer), exosphere and thermosphere as these two layers do not have much air. 

The gases present in the mesosphere create heat when a meteor or asteroid passes through this layer and burn them up, thus preventing these bodies from reaching the Earth’s surface. These burning meteors in the mesosphere can sometimes be seen in the sky at night as “shooting stars.”An estimate says that about forty tons of meteors fall towards the Earth every day. So, the mesosphere has a big job protecting the Earth.

Events in Mesosphere

• One of the interesting events which happen in the mesosphere is the swaying of the layer, which are identical to the waves in the ocean, owing to their trigger being the gravitational pull of the Moon.
• Another event that occurs in the layer is planetary waves, which begin in the troposphere and spread up towards the mesosphere. Planetary waves are huge wind movements caused by the planet’s rotation, causing the weather on Earth’s surface to change.
• The direction of wind inside the mesosphere is dependent on the altitude. The wind blows from North to South in the lower mesosphere and from East to West in the upper mesosphere.
• A phenomenon called “sprites” and “elves” occurs in the mesosphere caused due to lightning, sometimes giving a bright red effect to the sky.
• Another phenomenon called “airglow” happens in the mesosphere due to the five-kilometre sodium layer present in this sphere. This happens due to the presence of charged particles of approximately 4lakh/cubic centimetres, that emit light. This emission of light by atoms of the sphere is known as “airglow”. There is a continuous spread of light in the sphere on that particular spread of the layer. The region keeps getting the sodium from the meteors that come in the layer. This mentioned stretch is used in astronomical study to gather fine prints of the objects in the layer. They act as a reference point to study lesser bright objects.
• Mesosphere top side consists of layers that comprises metal also, some metals found here Iron and Potassium.

Dunes

In October 2018, a luminous emission of light was experienced in the Mesosphere layer at around  60 miles from the surface of the Planet. This light is known as “dunes”  as the same has considerable similarity with waves of sands observed in deserts. The emitted light seems to be greenish and looks like it is in a continuous flow towards the North Pole. As per the researchers observations, the reason for these emissions is solar light coming in contact with the electrically charged particles present in the layer. Additionally, the colour generated by these lights is green, resulting from the effects of rays from the sun on the O2. This is the reason these events are more apparent on higher elevation where O2 levels are greater.

Conclusion

The Mesosphere is the least known layer of the atmosphere because hot air balloons and aeroplanes do not  go that high to reach the layer due to increased drag of the atmosphere here. It is almost impossible for research equipment such as satellites to stay in orbit, making this sphere hard to study.