All about the Atmosphere

About 99% of total mass of atmosphere is within the height of 32 km from earth surface, rest above merges with outer space 
Atmospheric Air → Colourless, Tasteless, Odourless, Compressible, Mobile & Expandable
Atmospheric air mainly consists of -  
Nitrogen   →  78.03 % 
Oxygen     →  20.99 % 
Argon       →  .94 %
CO2         →  .03 % 
H             →   .01 % 

  • Rest are Neon, Helium, Ozone, Xenon & Krypton in very minute percentage 
  • Nitrogen
  • Major cause of atmospheric pressure, Force of wind & reflection of light 
  • Regulates combustion & avoids quick burning 
  • Dilutes oxygen and prevents rapid burning at the earth’s surface 
  • Nitrogen cannot be used directly from the air. 
  • The Nitrogen Cycle is nature’s way of supplying the needed nitrogen for living things
  • Get fixed to soil & generates protein in plants (Major source of food)
  • CO2.
  • Heaviest gas in atmosphere, essential for growth of vegetation 
  • Transparent to incoming solar radiations but opaque to terrestrial radiations radiated from earth surface which keeps air near the ground warmer 
  • Responsible for global warming, as alarming increase in level of CO2 in past few years due to burning of fossil fuels 
  • Water Vapour 
  • Form in atmosphere due to evaporation from surface water bodies 
  • Absorbs part of insolation from the sun & reduces its amount reaching the earth →Preserves earth’s radiated heat 
  • Hence, acts as a blanket, allowing the earth to neither become too hot or too cold 
  • Amount of water vapour decrease with altitude 
  • Amount of water vapour decreases from equator to poles 
  • Dust Particles 
  • Derived by strong winds from different sources on earth surface
  • Acts as hydroscopic nuclei around which water vapour condense & form clouds 
  • Intercept & reflect sun rays giving orange colour at sunrise, red colour at sunset & blue colour of clear sky 
  • Molecules (Dust particles) in air scatter blue light (shorter wavelength) more than red light (longer wavelength) in every direction, hence sky looks blue 
  • At sunrise & sunset, sky appears orange & red because blue light has already been scattered out by molecules in the air, out of sight & longer wavelength light reaches out to us 
  • Dense Haze & smog (smoke + fog) are also caused due to presence of dust particles in the air 
  • Structure of Atmosphere.
  • On the basis of chemical composition atmosphere can be divided into 2 parts viz. 

Homosphere  Upto 90 km (Uniformity in chemical composition) 
Troposphere 

Stratosphere
Mesosphere 

Heterosphere  Above 90 Km (non-uniformity in chemical composition) 
Ionsphere
Exosphere   
Each sublayer mentioned in these 2 layers is further divided by a shallow transitional zone ending with term “Pause” 


Troposphere

  • Average height is 16 Km → 10 km at Poles &upto 18 km at Equator.
  • Greatest at Equator due to upward transportation of heat by strong conventional currents.
  • That is why height of troposphere at a given latitude is greater in summer Temperature decreases with height, roughly at 1*C for every 165 meters → Normal Lapse Rate.
  • Lowest, Densest & contains 75 % of earth’s atmosphere with 90% of water vapours & dust particles.
  • All major atmospheric processes take place in this layer.

Tropopause 

Shallow transitional zone (Unstable zone) b/w Troposphere & Stratosphere (Approx. 1.5 Km) 
Temperature stops falling in this layer → – 80*C over equator & – 45*C over poles 

Stratosphere 

  • This layer rises upto 50 km (Thicker at Poles than at Equator) 
  • Temperature remains constant in its lower portion upto 20 Km & then gradually increases to 0*C till its upper limit i.e. 

Tropopause 

  • Increases mainly due to the presence of ozone gas, which absorbs sun’s UV rays
  • Practically no clouds, convection currents, Thundering or lighting, water vapours or dust particles hence airplane fly in this region
  • Few clouds called “Mother of Pearls / Narcreas” can be seen over Antarctica
  • Its lower portion (15 – 35 Km) constitutes Ozone layer which prevents us from harmful UV rays 
  • Amount of Ozone gas is found at Stratopause i.e. uppermost limit of Stratosphere

Mesosphere

  • Upto 80 ~ 90 Km, Temp. Decreases gradually with height until – 100 *C at 80 km 
  • Displays wispy clouds at high altitudes due to reflected sunlight from meteoric dust particles 
  • Most weather balloons are placed in this region 
  • Most meteors burn up in this layer; Upper limit Mesopause   

Ionosphere / Thermosphere 

•Extends up to 400 km, contains electrically charged particles (ions) with max. conc. at 250 Km 
•starts rising with increase in height because of ionization by solar radiations 
•Zone of Earths Satellites 
•Auroras →Are formed when Earth’s magnetic field traps solar winds in atmosphere, resulting in collision b/w solar wind & atmospheric charged molecules (ions)  
•Aurora Borealis → Northern light in northern hemisphere (Arctic circle)
•Aurora Australis → Southern light in southern hemisphere (Antarctic Circle)  
•All radio waves are reflected in this layer (Radio transmission)  
•D layer → Reflects signal of low frequency & absorbs of medium & high frequency 
•E layer (Kennedy Heaveside layer) →Reflects medium & high frequency radio waves to earth 
•F layer (Appleton layer) →Useful for long distance radio transmissions → reflects medium & high frequency radio waves to earth 
•G layer → Highest layer.
   
Depletion of Ozone Layer

•Major cause → CFCs (mainly from Refrigerator, AC, Spray Cans, Plastic Packaging, Cleaning Fluids, Insulation materials)
•UV breaks CFCs & release Chlorine atom which reacts with Ozone & convert it into simple oxygen molecule, which is unstable to absorb UV rays 
•Space probes are also responsible for depletion of Ozone layer, as every time a rocket is fired into space, 70 – 150 tons of Chlorine is injected into atmosphere 
•Another cause for ozone layer depletion is oxides of Nitrogen, esp. Nitric oxide, released from supersonic aircrafts, automotive exhaust, in form of nitrates in fertilizers etc.
•Already a major Ozone hole is formed over Antarctica with risk countries New Zealand, Australia, South Africa, Chile, and Argentina etc. 

Auroras 

•Solar flares from Sun (leaving black spots on sun) entering Ionosphere forms Auroras in N & S poles. 
•The auroras appear as sheets of illuminated curtains with streaks or as bright arcs in the sky. 
•These lines or arcs are in the form and directions of the magnetic lines of force of the earth; indicating the involvement of moving charge particles under the influence of concentrated magnetic field of the earth. 
•When they reach the earth, they get concentrated near the poles because of the strong axial magnetic fields there. 
•In other regions of the earth, the magnetic field is weaker and so the aurora does not form although the emission of the solar wind particles takes place uniformly. 
•There is an 11-year solar cycle (on average) that controls the tempo of the aurora. The most recent peak in the cycle occurred in 2000-2001. The next peak is predicted in 2013 – 2014.
Solar Tsunami 

When solar flares are at peak 
•Can disrupts ions in Ionosphere affecting radio waves, GPS 
•Can burn the satellites 
•Can causes skin cancer in human being 
•Increase the frequency of El Nino – Warming of the Oceans
•Can burn transformers

All The Best !!!!

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