Now, we are clear on where Earth stands in the Solar System after the last blog: Sun and the Other Small Things. Going forward, let us find out what is immediately around the Earth. We know that as per the conditions of a Planet, every planet should have enough gravity to attain round shape(hydrostatic equilibrium) and clear the space around its own orbit. So, this means we can take it for granted that Earth has considerably strong gravitational field.
Atmosphere is layer of gaseous mixture surrounding the Earth. This layer is retained by the pull of Earth's gravity. Atmospheric layer extend up to 100,000 kms above the surface of Earth. It is important to know that Earth's atmosphere doesn't abruptly end after 100,000 kms, but rather become lighter and lighter and slowly disappears as we go farther from the Earth's surface. Hence, the density/thickness of atmosphere will be highest at the surface of Earth and decreases gradually as we go farther and gradually nullifies after 100,000 kms above the surface. Atmosphere consists of several layers. It is fundamental to know on what basis these layers are divided and so on. As we travel away from the Earth's surface:
At first, the temperature starts decreasing and reaches point (A) and then,
It starts increasing until point (B) then again,
It starts decreasing until point (C) and then finally,
It starts increasing from there on.
We shall get in to the reason behind such temperature inversion patterns as we proceed. However, for now, it is to be understood that on the basis of this Temperature Inversion the atmosphere is divided in to FOUR parts.
Troposphere (0-12 kms): All the weather conditions that we see everyday occur in this region of the atmosphere. The height of the Troposphere varies from Equator to Poles. At Equator it is 17 kms and at poles it is 9 kms. The reason behind this height difference is very important to understand further concepts on Weather.
Further, the temperature graph steadily decreases in Troposphere as we move away from the surface of the Earth.
- There will be 6.5˚ C fall for every 1 Km we travel away from the Earths' surface. This is called Normal Lapse Rate(NLR). Troposphere contains mainly dust particles and water vapor.
- At the top of Troposphere; near tropopause the temperature touches as low as -85˚C.
- 90% of the water vapor present in the air is within 6 kms and 99% is within 12 kms from the Earth's surface.
- Troposphere comprises of 75% of entire atmospheric mass.
- Almost all the visible clouds we see are a part of Troposphere. This is the most important layer of the atmosphere with respect to living beings due to the presence of weather in this region.
Tropopause(12-14 kms above the surface) : Tropopause is a layer of 1.5-2 kms in thickness and is formed above the Troposphere(extends up to 12 kms). The temperature no more falls in tropopause. This is considered as an unstable layer and above the Tropopause the temperature begins to raise in Stratosphere. This inversion in temperature prevents further convection of air. Thus, confining most of the world's weather to Troposphere.
Read further- Around the Earth- Part II
Atmosphere is layer of gaseous mixture surrounding the Earth. This layer is retained by the pull of Earth's gravity. Atmospheric layer extend up to 100,000 kms above the surface of Earth. It is important to know that Earth's atmosphere doesn't abruptly end after 100,000 kms, but rather become lighter and lighter and slowly disappears as we go farther from the Earth's surface. Hence, the density/thickness of atmosphere will be highest at the surface of Earth and decreases gradually as we go farther and gradually nullifies after 100,000 kms above the surface. Atmosphere consists of several layers. It is fundamental to know on what basis these layers are divided and so on. As we travel away from the Earth's surface:
At first, the temperature starts decreasing and reaches point (A) and then,
It starts increasing until point (B) then again,
It starts decreasing until point (C) and then finally,
It starts increasing from there on.
We shall get in to the reason behind such temperature inversion patterns as we proceed. However, for now, it is to be understood that on the basis of this Temperature Inversion the atmosphere is divided in to FOUR parts.
 |
| A- 10 kms, B- 48 kms, C- 80 kms |
- Troposphere - From surface level to point A.
- Stratosphere - From Point A to Point B.
- Mesosphere - From Point B to Point C.
- Thermosphere - From Point C to space.
Composition of Atmosphere: Atmosphere mostly comprises of what we generally call - air. Air has:
78.09% of Nitrogen,
20.95% of Oxygen,
0.93% Argon,
0.039% Carbon Dioxide and other gases in lesser compositions. Further, it is said to have up to 1% of water vapor over the sea level and 0.4% over the entire atmosphere. 90% of the total atmosphere will be present within 20 kms from the surface of the Earth. This is due to obvious high gravity present near the Earth's surface.
Troposphere (0-12 kms): All the weather conditions that we see everyday occur in this region of the atmosphere. The height of the Troposphere varies from Equator to Poles. At Equator it is 17 kms and at poles it is 9 kms. The reason behind this height difference is very important to understand further concepts on Weather.
'At poles the temperature is low compared to Equator. This makes air more dense at the poles and light at the equator. Now, consider the air at poles and air at the Equator as two columns of air. Now, to achieve same atmospheric pressure, colder air at the poles occupies lesser volume as compared to hotter air at the Equator. So, the hotter air mass at the Equator tries to balance its temperature, volume and pressure, with the colder air at the poles so that they can achieve equilibrium. The result of such 'trials to achieve equilibrium' or 'transport of air' drives the whole concept of Weather!'
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| Red column- Equator Blue column- Poles |
- There will be 6.5˚ C fall for every 1 Km we travel away from the Earths' surface. This is called Normal Lapse Rate(NLR). Troposphere contains mainly dust particles and water vapor.
- At the top of Troposphere; near tropopause the temperature touches as low as -85˚C.
- 90% of the water vapor present in the air is within 6 kms and 99% is within 12 kms from the Earth's surface.
- Troposphere comprises of 75% of entire atmospheric mass.
- Almost all the visible clouds we see are a part of Troposphere. This is the most important layer of the atmosphere with respect to living beings due to the presence of weather in this region.
 |
| This cartoon shows some of the gases in Earth's troposphere. There is more nitrogen (N2) than anything else. There is also a lot of oxygen (O2). The cartoon also shows carbon dioxide (CO2), water vapor (H2O), methane (CH4), sulfur dioxide (SO2), and carbon monoxide (CO). Image courtesy UCAR, |
Tropopause(12-14 kms above the surface) : Tropopause is a layer of 1.5-2 kms in thickness and is formed above the Troposphere(extends up to 12 kms). The temperature no more falls in tropopause. This is considered as an unstable layer and above the Tropopause the temperature begins to raise in Stratosphere. This inversion in temperature prevents further convection of air. Thus, confining most of the world's weather to Troposphere.
Read further- Around the Earth- Part II
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