Structure of Atmosphere ? What are the five different types of atmosphere ?

Structure of Atmosphere

The earth’s atmosphere is made up of five imaginary layers which are categorized on the basis of density, temperature, variation and altitude. They are: Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.

 

a. Troposphere

Troposphere is the first, nearest and the densest layer of the atmosphere. It is also the most polluted layer because of human activities. It extends up to 16 km from the earth surface. Troposphere contains different gases like nitrogen, oxygen, carbon dioxide, water vapor, dust particles and other particulates. This layer is also called variable layer because of the continuous change in the temperature and weather conditions. This layer also causes weather phenomena like the dew formation, snow fall, frost, rain, hurricances. Wind, etc. due to which this layer is very important to meteorologists. About 95% of all the components found in the atmosphere are found here. The temperature decreases with the increase in altitude in troposphere because of the decrease in the air pressure and density of the particulate matters. Every kilometer increase in altitude decreases a temperature by 6.5 degree. The boundary of this layer is called tropopause, where the temperature remains relatively constant. Thus, troposphere is an imaginative sphere which separates troposphere from the stratosphere. It has -56 degree celcius.

 

b. Stratosphere

Stratosphere is the second layer of the atmosphere that extends from 16-50 km above the earth’s surface with a thickness of about 34 km. The main constituents of this layer are oxygen, nitrogen and ozone. Within 20-30 km from the earth’s surface, this layer contains ozone gas. This layer is also called the ozonosphere. The ozone layer is very important for living organisms on the earth because it absorbs and reflects the harmful UV radiation. UV radiation can cause skin cancer, blindness, destroys food production of the plants, etc. The formation of clouds is very thin and low in this sphere. Thus, there is good visibility and the layer is calm. So, the jet planes prefer to fly in this layer. As altitude increases, the temperature also increases in stratosphere. This is because there is ozone layer which absorbs most of the UV radiation. Temperature varies in this layer from -56 degree celcius to -2 degree celcius. The upper boundary of this layer that separates it from mesosphere is called stratopause. It has -2 degree celcius.

 

c. Mesosphere

Mesosphere is present just above the stratopause. It extends from 50-80 km above the earth’s surface with a thickness of about 30 km. gases like nitrogen, oxygen and ozone etc. are found in this region. This layer is very stormy and coldest layer because winds blow from the west to east in the winter and from east to west in the spring throughout the year. Moreover, there is no adequate ozone gas that traps heat. Temperature varies from -2 degree celcius to  -109 degree celcius. Occasionally, foreign objects like meteors pass through the upper hot layers and strike the cold mesosphere suddenly causing them to produce hot streaks of gases. The hot streaks of gases produced when meteors falls through atmosphere is called meteor shower. The upper boundary of mesosphere is called mesopause which has temperature -109 degree celcius.

 

d. Thermosphere

Thermosphere is the second last layer of the atmosphere. It extends from 80-720 km with the thickness of about 640 km. It contains gases like Hydrogen and Helium in the upper region while in lower regions, it contains nitrogen, oxygen and nitrogen, etc. At a height of about 80-550 km from the earth surface, nitrogen and hydrogen are ionized in this layer by solar radiation. So, this layer is called ionosphere. These ionized particles reflect the high frequency (HF) and short wave (SW) radio signals back to the earth and help in long distance communication. Thermosphere is very hot in the upper region because of extremely thin air density that absorbs solar radiation. Temperature varies between -109 degree celcius to 1200 degree celcius. The upper boundary of this layer is called thermopause. The international space station revolves around the earth in thermosphere.  In the northern and southern hemisphere of the earth, the charged particles from the sun strike the ionized nitrogen and oxygen producing lights of different colors. These are called polar lights. The polar light in the northern hemisphere is called aurora. The Aurora Borealis and Aurora Australis are seen in the northern and southern hemispheres, respectively. The aurora is seen only at night from the northern and southern hemisphere because the charged particles of the sun that strike the earth are drawn towards the polar regions by the earth’s magnetic field and are too dim to be seen during the day.

 

e. Exosphere

Exosphere is the topmost layer of the atmosphere. It has very thinly distributed atoms of hydrogen and helium in the upper region and oxygen, nitrogen and carbon dioxide in the lower regions. This layer is very hot as temperature can vary between 1200 degree celcius to 6000 degree celcius. Exosphere extends beyond 720 km above the earth’s atmosphere. It is the uppermost layer and does not have an upper boundary because there is not distinct region from which the atmosphere is separated from the space. So, it is also called the fringe region. The density of air in this layer is extremely low that molecules moving at high speeds rarely collide with each other.