Explain the structure of the atmosphere. Pls help
Answers
Our atmosphere is divided into five layers starting from the earth's surface. These are Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.
Troposphere
The troposphere is the lowest layer of our atmosphere. Starting at ground level, it extends upward to about 10 km (6.2 miles or about 33,000 feet) above sea level. We humans live in the troposphere, and nearly all weather occurs in this lowest layer. Most clouds appear here, mainly because 99% of the water vapor in the atmosphere is found in the troposphere. Air pressure drops, and temperatures get colder, as you climb higher in the troposphere.
Stratosphere
The next layer up is called the stratosphere. The stratosphere extends from the top of the troposphere to about 50 km (31 miles) above the ground. The infamous ozone layer is found within the stratosphere. Ozone molecules in this layer absorb high-energy ultraviolet (UV) light from the Sun, converting the UV energy into heat. Unlike the troposphere, the stratosphere actually gets warmer the higher you go! That trend of rising temperatures with altitude means that air in the stratosphere lacks the turbulence and updrafts of the troposphere beneath. Commercial passenger jets fly in the lower stratosphere, partly because this less-turbulent layer provides a smoother ride. The jet stream flows near the border between the troposphere and the stratosphere.
Mesosphere
Above the stratosphere is the mesosphere. It extends upward to a height of about 85 km (53 miles) above our planet. Most meteors burn up in the mesosphere. Unlike the stratosphere, temperatures once again grow colder as you rise up through the mesosphere. The coldest temperatures in Earth's atmosphere, about -90° C (-130° F), are found near the top of this layer. The air in the mesosphere is far too thin to breathe; air pressure at the bottom of the layer is well below 1% of the pressure at sea level, and continues dropping as you go higher.
Thermosphere
The layer of very rare air above the mesosphere is called the thermosphere. High-energy X-rays and UV radiation from the Sun are absorbed in the thermosphere, raising its temperature to hundreds or at times thousands of degrees. However, the air in this layer is so thin that it would feel freezing cold to us! In many ways, the thermosphere is more like outer space than a part of the atmosphere. Many satellites actually orbit Earth within the thermosphere! Variations in the amount of energy coming from the Sun exert a powerful influence on both the height of the top of this layer and the temperature within it. Because of this, the top of the thermosphere can be found anywhere between 500 and 1,000 km (311 to 621 miles) above the ground. Temperatures in the upper thermosphere can range from about 500° C (932° F) to 2,000° C (3,632° F) or higher. The aurora, the Northern Lights and Southern Lights, occur in the thermosphere.
Exosphere
Although some experts consider the thermosphere to be the uppermost layer of our atmosphere, others consider the exosphere to be the actual "final frontier" of Earth's gaseous envelope. As you might imagine, the "air" in the exosphere is very, very, very thin, making this layer even more space-like than the thermosphere. In fact, air in the exosphere is constantly - though very gradually - "leaking" out of Earth's atmosphere into outer space. There is no clear-cut upper boundary where the exosphere finally fades away into space. Different definitions place the top of the exosphere somewhere between 100,000 km (62,000 miles) and 190,000 km (120,000 miles) above the surface of Earth. The latter value is about halfway to the Moon!
1. Troposphere:
This is the lowest layer of atmosphere and it is very important for all the living organisms because all the activities and aspects related with weather e.g. Evaporations, condensation, precipitation, storm, lightening etc. originate in this sphere. Around 75% mass of gases and nearly all water vapours and aerosols are present in this layer.
2. Stratosphere:
This sphere starts from 12 to16 kilometers above the Earth surface and extend upto 50 kilometers known for isothermal characteristics also. Although scientists have different views about the height, width and temperature but they all agree on one point that at the lower layer of this sphere temperature does not change with increase in height but at the height of 20 KM in upper stratosphere temperature starts increasing because of absorption of ultra-violet rays by ozone gases. At the height of 50 KM it becomes 0° Celsius (32°F).
Region where ozone gas is present in abundance is also known as ozone layer. This gas is present in abundance between 15 to 35 kilometers above the Earth surface, which originates when oxygen molecule disintegrates into two atoms of oxygen and then integrating back into a molecule. Molecules of ozone layer are not stable, their origin and disintegration is a gradual and continuous process.
3. Mesosphere:
Above the upper boundary of stratosphere, which extends from 50 kms. above surface of Earth, is mesosphere, upto 80 kms. In this layer temperature again starts decreasing with the increase in height and at the upper boundary of this layer it touches down to -80°C point. Air pressure is very low in this layer. At the height of 50 kms it is 1 mb and at height of 80 kms it drops to 0.01 mb.
4. Ionosphere:
The height of this sphere extends from 80 to 640 kms above surface of Earth. Credit of discovering this layer goes to scientists Kennelly and Heaviside who, with the help of radio waves proved that the atoms and molecules of the gases present in this layer get electrically changed by the addition and removal of electrons due to the effect of ultraviolet, Xray and Gama rays.
Short wavelength rays of solar energy (UV, X, L) get absorbed by molecules and atoms of nitrogen and oxygen because of which temperature increases upto 1000°C in this scanty pressure layer of atmosphere. Because of scanty air pressure, temperature here is quite different as compared to the temperature felt at the surface of Earth.
5. Exosphere:
This is the outermost layer of atmosphere and we do not have much information about this layer. It lies above the height of 640 kms. Only Helium and hydrogen are found in this layer. Moreover the density of this layer is very low.