2 Important Layers of the Atmosphere : Stratosphere and Troposphere

2 Important Layers of the Atmosphere : Stratosphere and Troposphere

Stratosphere and Troposphere

Stratosphere

stratosphere
White layer depicts the stratosphere, Blue layer depicts the mesosphere, orange layer depicts the troposphere. Image source: NASA/Crew of Expedition 22 – http://spaceflight.nasa.gov/gallery/images/shuttle/sts-130/html/iss022e062672.html http://www.nasa.gov/multimedia/imagegallery/image_feature_1592.html

The stratosphere is regarded as the second layer of Earth’s atmosphere (between the Troposphere and the mesosphere) as we move upwards from the surface.

What is the height of the stratosphere?

The stratosphere lies at the height of about 6.2 miles (10 km or 33,000 feet) above the surface at middle latitudes and extends to a height of 31 miles (50 km). Near the equator region, the stratosphere boundary lies at the height of 12 miles or 20 km, whereas, near the poles, the layer starts at the height of just 4 miles or 7 km. The stratosphere’s upper periphery is termed as the stratopause, and the lower periphery is termed as the tropopause. 

What is the composition of the stratosphere?

When compared to the air composition at sea level, the stratosphere is a thousand time less dense.

Ozone Layer:

The layer houses one of the essential types of oxygen molecule i.e., O3 or Ozone. The presence of ozone molecules in abundance helps absorb the energy from the ultraviolet radiation of the Sun. This absorption of energy leads to the heating up of the layer as we move upwards. This temperature pattern is precisely opposite of that in the Troposphere where temperature drops with an increase in altitude. As a result of temperature stratification, the stratosphere experiences a comparatively little convection. Hence, the layer of air in this region is relatively still/stable. This helps commercial jet aircraft to fly without turbulence in the lower stratosphere.

Water vapor concentration:

Low. As the stratosphere lies much higher than the surface, the amount of water vapor available is very low. This is the reason behind the appearance of fewer clouds in these regions. Major cloud formation takes place in the humid layer beneath the Troposphere. However, PSCs or Polar stratospheric clouds, also termed as nacreous clouds, can be found in the lower stratosphere of the regions near the poles. These clouds appear when the temperatures drop below -78 degrees Celsius at the height of 9.3 to 15.5 miles or 15 to 25 km. These clouds aid in forming holes in the ozone layer by producing chemicals that damage the ozone molecules.

CFCs:

The absence of strong vertical convection in the stratosphere region causes gases and other materials to remain stagnant for a long time. An example of such chemicals residing in the stratosphere is the CFCs (chlorofluorocarbons). CFCs absorb the UV radiations to break down a chlorine atom from its molecule. This chlorine atom then reacts with the ozone molecule and breaks it into an oxygen molecule and a chlorine monoxide molecule. As a result of this, the ozone gets destroyed, leading to the depletion of the protective layer.

CFCs are thrown into the stratosphere by massive volcanic eruptions, aerosol spray cans, industrial cleaning products, air conditioners, and major meteorite impacts. These chemicals remain there for months creating ozone holes creating issues to the Earth’s climate.

2 Important Layers of the Atmosphere : Stratosphere and Troposphere
Ozone layer depletion (violet-blue depicts deficiency of ozone)
NASA, Agujero en la capa de ozono 2008, marked as public domain, more details on Wikimedia Commons

Rocket launches, aircraft shoot up toxic gases into the stratosphere, impacting the Earth’s climate severely. Energy waves from the Troposphere also climb up to the layer and cause heating of the layer. Lower regions of the layer experience types of electrical discharge similar to lightning.  

Troposphere

troposphere
Troposphere
Image source: wikimedia commons NASA Earth Observatory – http://eol.jsc.nasa.gov/scripts/sseop/photo.pl?mission=ISS013&roll=E&frame=54329

“Tropos” means change. The lowermost layer of the Earth’s atmosphere gets its name due to its ever-changing/evolving weather conditions. The Troposphere is located directly below the stratosphere, and its upper boundary is termed as the tropopause

What is the height of the Troposphere?

The Troposphere starts from the sea level and extends to a height of 6.2 miles (10 km or 33,000 feet) at middle latitudes. Near the equator region, the troposphere boundary lies at the height of about 18 km, whereas, near the poles, the layer starts at the height of just 7 km. The layer is the thinnest near the poles and thickest near the equatorial regions. 

What is the composition of Troposphere?

2 Important Layers of the Atmosphere : Stratosphere and Troposphere
Troposphere composition Image source: Mysid – Vectorized version of w:Image:Atmosphere gas proportions.gif (originally by Brockert).

The Troposphere contains 75% of the total mass of the Earth’s atmosphere.

 Water vapor concentration:

The Troposphere holds 99% of the total water vapor of the atmosphere. This is the reason why major cloud formation processes take place in this layer. Almost all clouds (storm clouds, rains clouds, white clouds, etc.) form in this layer. However, the distribution of water vapor in the Troposphere is highly uneven. Humidity varies with latitude, temperature, and terrain. 

Nitrogen:

The troposphere air is made up of 78% nitrogen. Nitrogen composition is fairly even throughout the Troposphere. 

Oxygen:

The troposphere air is made up of 21% oxygen. Oxygen composition is relatively even throughout the Troposphere, with little variations occurring with altitude and industrial factors. Forest covered regions like the Amazon serve as oxygen-rich areas. 

Other gases:

Gases like carbon dioxide, argon, carbon monoxide, and a negligible amount of a number of other gases are also present in the Troposphere. 

The temperature of the Troposphere decreases with increase in altitude. With a decrease in temperature, the vapor pressure of the layer also decreases. 

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

About Sanchari Chakraborty

2 Important Layers of the Atmosphere : Stratosphere and TroposphereI 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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