WHAT IS ATMOSPHERE ? | GEOGRAPHY

ATMOSPHERE
ATMOSPHERE

The envelope of air that completely surrounds the Earth is known as atmosphere.
The atmosphere extends to about 1000 km from the surface of the Earth.But 99% of the total mass of the atmosphere is found within 32 km.
Atmosphere contains life giving gases, like oxygen for man and animal, and carbon-dioxide for plants.
It also acts like a blanket, like greenhouse and thus keeps the Earth warmer then it would otherwise be.
It regulates the heat balance of the Earth and also protects us from the harmful ultraviolet radiation of the Sun. and serves a storehouse for water vapour, which leads to precipitation and hence, facilitates the hydro-logical cycles.

Composition of Air

Nitrogen
78.03
Oxygen
20.99
Argon
0.93
Carbon dioxide
0.03
Hydrogen
0.01
Neon
0.0018
Helium
0.0005
Krypton
0.0001
Xenon
0.000005
Ozone
0.0000001

STRUCTURE OF ATMOSPHERE

The Atmosphere can be divided into five zones

TROPOSPHERE

This is the layer nearest to Earth’s Surface.
All weather Phenomenon occur here.
Thickness varies 8 km at poles to 16 km at equator.
Water vapour and dust exist in this layer.
In this at every 165 m there is a drop of 10 C (Normal Lapse Rate of Temperature).
Tropopause separates troposphere from stratosphere.
Height of troposphere change according to season in summer it goes high in winter down’s low.

STRATOSPHERE

Region of uniform temperature extending from 16 km to 50 km height.
Free from cloud, dust and water vapour.
It’s average height is 20-50 km.
This is the layer where Aeroplane flies.
This sphere is free from any climate changes.
Contains ozone (25-30 km from earth’s surface) region being called ozonosphere.
Ozone absorbs the ultra-violet rays from the Sun.This layer has a comparatively higher temperature due to the absorption of ultraviolet radiation from the Sun.(Temperature increases as we go up).
Stratopause separates stratosphere from mesosphere.

MESOSPHERE

Mesopause separates mesosphere from ionosphere.Up to height of about 80 km.
In this sphere temperature is decreased with increase in height and falls to about 10000 C at 80 km height.

IONOSPHERE (THERMOSPHERE)

Up to a height of about 500-600 km.
Due to presence of large amount of ions present in this sphere cosmic rays are present here.
Because of presence of this sphere it reflects radio waves back to the Earth.This makes radio communication possible.It protects Earth from falling meteorites as most of them burn out in this region.

EXOSPHERE

Upper limit of this sphere is quite uncertain.
In this sphere Earth gravity is extremely weak.
The outer part of exosphere is called magnetosphere.
Van Allen’s Radiation Belts.The ionized particles pressure increase in frequency with atmosphere having a high concentration of ionized particles.This is the last sphere of the atmosphere.
The final boundary between the Earth and the outer space is called “Magnetopause”.

WEATHER AND CLIMATE

Weather is the description of the atmosphere condition of a particular place at a particular time for a short period of time.
Climate is the composition of integrated picture of the weather conditions over a long period of time.
Climate data is based on calculated averages of data recorded over a period of 35 years. The classical period of 30 years, as defined by WMO.

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