Mesosphere: the 3rd layer of the atmosphere

MESOSPHERE

The Mesosphere is regarded as the third layer of the atmosphere of the Earth as we move upwards from the surface. The word “mesos” means the middle in Greek. The layer is called so because it is present precisely in the middle of the layers of Earth’s atmosphere. It lies directly over the stratosphere and beneath the thermosphere.

What is the height of the mesosphere?

The mesosphere lies at the height of about 31 miles (50 km) above the surface at middle latitudes and extends to a height of 53 miles (85 km). Near the equator region, the mesosphere boundary lies higher, whereas, near the poles, the layer starts at a much lower height. The height also varies with seasons, the layer is higher during winters and lowers during summers. The layer’s lower periphery is termed as the stratopause, and the upper periphery is termed as the mesopause.

What is the temperature of the mesosphere?

As we move upwards in the mesosphere, the temperature tends to decrease. The decrease in temperatures occurs due to the reduction in solar energy absorption and cooling by CO2 radiative emission. The coldest temperatures in the atmosphere, around -130°F or 90°C, are present near the topmost part of the mesosphere (i.e., the mesopause). This temperature can vary with latitude and season.

What is the composition of the mesosphere?

Meteoroid Vaporization:

Most of the meteors that fall towards the Earth, get vaporized in the mesosphere. Some meteor particles also float in this layer after losing its energy. As a result, the layer is comparatively high in iron, potassium, sodium, and other metal concentrations. The upper mesosphere contains a thin layer of metals like iron and potassium.

Aurora:

In recent years, a distinct form of aurora has been observed in the layer about 96km above the surface. These aurorae appear in the shape of sandy ripples seen in the beaches and are therefore called dunes. The dunes produce a green color as a result of the interaction of oxygen molecules with solar particles. 

Noctilucent clouds:

mesosphere
Noctilucent clouds
NASA/HU/VT/CU LASP, Northpoleclouds AIMData c, marked as public domain, more details on Wikimedia Commons

Noctilucent clouds, sometimes referred to as polar mesospheric clouds, form high up in the layer near the poles. The formation of clouds at such a height and in the presence of negligible water vapor .Although not much is known about this band, the meteoric smoke is believed to aid such clouds’ formation.

Sodium layer:

The mesosphere contains a 5km deep sodium layer at the height of 80-105 km. The sodium atoms present in this layer are mainly non-ionized and unbound. The sublimating meteors bring this sodium supply in the layer. This band also contributes to the airflow. 

Atmospheric tides/waves:

This layer experiences strong zonal winds that direct from east to west and atmospheric tides and planetary waves. These tides and waves reach the mesosphere after propagating through the stratosphere and the troposphere. Once, these waves reach this layer, it amplifies and begins to dissipate. As a result of this dissipation, the layer receives momentum that drives global circulation. 

Ionosphere (D layer):

The upper layer of the mesosphere is termed as the ionosphere. The ionosphere is called so because, under the influence of solar radiation, ionization of gases occurs in this layer. During the day, ionization of nitric oxide by Lyman series-alpha hydrogen radiation takes place in this layer. This ionization is very weak and has a high recombination rate. When the solar radiations are unavailable, the ionization stops. This layer is also known for attenuating medium frequency radio waves. 

Sprites:

The layer experiences occasional lightning-like electrical discharges tens of kilometers above the thunderclouds. This is referred to as “sprites” or “ELVES”.

The stratosphere and mesosphere are, at times, termed as the middle atmosphere together. Due to turbulence, the atoms and molecules gases present in the mesopause get mixed. Whereas, beyond the mesosphere, gases suffer minimal collisions in the thermosphere, so they become somewhat detached.

Compared to the other layers of the atmosphere, the mesosphere is challenging to study. Most of the aircraft and weather balloons are unable to reach such heights. Satellites and spacecraft tend to orbit above this layer and can, therefore, not gain much information about this layer. Scientists and researchers use sound rockets to study the layer. But the frequency of such research is less, and this layer continues to be mysterious. 

To know more about the layers of Earth’s atmosphere Click here

About Sanchari Chakraborty

I am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

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