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Atmosphere Notes of Geography section for UPSC and Other Exams


SSBInsights Team
11 Nov 2017
exams

Notes of  Atmosphere

Composition of the Atmosphere Nearly 99% of the volume of atmosphere is composed of various gases. Nitrogen and oxygen are the most predominant gases. The major gases that form the bulk of the volume of dry air are as follows:    Nitrogen 78.088%, Oxygen           20.949%, Argon 0.930% and Carbon dioxide 0.030%. The remaining gases are neon, helium, krypton, xenon, ozone, hydrogen, methane and nitrous oxide. Together they form the remaining 0.003% of the volume of air.

TROPOSPHERE The troposphere is the lowest layer of Earth's atmosphere. It starts at Earth's surface and goes up to a height of 7 to 20 km (23,000 to 65,000 feet) above sea level. Most of the mass (about 75-80%) of the atmosphere is in the troposphere. Nearly all of the water vapor and dust particles in the atmosphere are in the troposphere. That is why most clouds are found in this lowest layer, too. In fact most weather phenomenon such as thunder, lightening, precipitation etc are observed in troposphere.  The bottom of the troposphere, right next to the surface of Earth, is called the "boundary layer". In places where Earth's surface is "bumpy" (mountains, forests) winds in the boundary layer are all jumbled up. In smooth places (over water or ice) the winds are smoother. The winds above the boundary layer aren't affected by the surface much.

The boundary between the top of the troposphere and the stratosphere (the layer above it) is called the tropopause. The height of the tropopause depends on latitude, season, and whether it is day or night. Near the equator, the tropopause is about 20 km (65,000 feet) above sea level. In winter near the poles the tropopause is much lower. It is about 7 km (23,000 feet) high. The jet stream is just below the tropopause.

Stratosphere The top of the stratosphere occurs at 50 km altitude.

Ozone is relatively abundant in the stratosphere, at about 25 to 30 km from the surface of the earth. This portion of troposphere is also called Ozonosphere. It absorbs energy from incoming ultraviolet radiation from the Sun. In the lower stratosphere the temperature is practically constant or increases slightly with altitude. Within the ozone layer the temperature rises more rapidly, and the temperature at the upper boundary of the stratosphere, almost 50 km above sea level, is about the same as the temperature at the surface of the earth. Commercial jet aircrafts fly in the lower stratosphere to avoid the turbulence which is common in the troposphere below.

The stratosphere is very dry; air there contains little water vapor. Because of this, few clouds are found in this layer; almost all clouds occur in the lower, more humid troposphere. Polar stratospheric clouds (PSCs) are the exception. PSCs appear in the lower stratosphere near the poles in winter. They are found at altitudes of 15 to 25 km and form only when temperatures at those heights dip below -78° C.

The mesosphere starts at 50 km above Earth's surface and goes up to 85 km high. As you get higher up in the mesosphere, the temperature gets colder. The top of the mesosphere is the coldest part of Earth's atmosphere. The temperature there is around -90° C (-130° F)!

Scientists know less about the mesosphere than about other layers of the atmosphere. The mesosphere is hard to study. Weather balloons and jet planes cannot fly high enough to reach the mesosphere. The orbits of satellites are above the mesosphere. We don't have many ways to get scientific instruments to the mesosphere to take measurements there.

 

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