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CLIMATOLOGY

1/18/2017

Atmosphere is mixture of different gases and it envelopes the earth all around. It contain life giving gases like oxygen for humans and animals, and carbon di oxide for plants. Air is a mixture of gases dominated by nitrogen and oxygen, Water vapor, another important constituent, can condense into clouds of liquid water droplets. The air is an integral part of the earths mass and 99% of total mass of atmosphere is confined to the height of 32 km from the earth surface. Atmosphere is composed of GASES, Water Vapour and Dust Particles

DR. D.D. SHARMA DAV COLLEGE, CHANDIGARH

TROPOSPH ER E: Troposp here is lower most layer. Average height is 13 km, roughly height near poles is 8 km, about 18 km at equator. Thickness of Tropo sphere is greatest at the equator because heat is transported to great height by convectional currents. This layer contains water vapour and du st particles. All climatic and weather mechanism took place in this layer. Temperature decreases for 6.5 degree C at 1000m. Or 1 degree C at 165 m This is most important layer for all biological activity. The zone separating Troposphere from Stratosphere is called Tropopause. Temperature at Tropopause is about minus 80 degree C. over equator and about minus 45 degree C over poles. The tem perature here nearly con stan t he nce, it is called Tropopause

STR ATOSPH ERE: The Stratosphere is found above the Troposphere, extends up to about 50 km. This layer contains OZO NE Layer. Ozone layer absorbs ultra-violet rays and shields earth from intense and harmful effect of energy. Temperature increases with altitude. This layer transits in to Mesosphere from Stratopause

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MESOSPH ER E: The Me sos phere lies above the Stratosphere. Extends up to height of 80 km. Here Temperature starts to decrease with altitude and reaches up to minus 100 degree C. at the height of 80 km. The upper limit of Mesosphere is known as Mesopause. THERMO SPHE RE: A tmo sp here beyon d mesop au se w herein temperat ure increases rapidly. Low den sity of G as. T his layer is divided in to two layers IONO SPHE RE: The Ionosphere lies between 80 km to 400 km above Mesopau se. It contains electrically charged particles known as ions, hence called ionosphere. Radio waves transmitted from the earth are reflected back to earth by this layer. Temperature increases with height. The uppermost layer of t he Iono sphere is known as Exo sp here. This is highest layer but little known about it.

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1/18/2017

CHEMICAL COMPOSITION OF ATMOSPHERE:

HOMOSPHERE

Represents Lower part of the atmosphere (Troposphere, Stratosphere, Mesosphere). Main gases are Oxygen (21%), Nitrogen (78%). This is called Homosphere because of homogeneity of the proportion of various gases.

HETROSPHERE

Extends from 90 km to upper limit of atmosphere. Layers vary in chemical and physical proportion. It comprises of Thermosphere (Ionosphere + Exosphere).

WATER VAPOUR Water vapour is variable element in the atmosphere which decreases with altitude. In the warm and wet tropics it may account for 4% of the air by volume, while in the dry and cold areas of desert and polar regions, it may be less than 1% of the air. Water vapour decreases from the equator towards poles. It also absorbs part of the Insolation and preserves the earths radiated heat. Thus it acts like a blanket allowing the earth neither to become too cold nor too hot. Water vapour also contributes to the stability and instability in the air.

DUST PARTICLES Atmosphere has sufficient capacity to keep small solid particles, which may originate from different sources and include sea salt, fine soil, smoke, ash, pollen, dust and integrated particles of meteors. Dust particles are generally concentrated in the lower layers of the atmosphere yet, conventional air currents may transport them to great height. The higher concentration of dust particles are found in sub-tropical and temperate regions due to dry winds in comparison to equatorial and polar regions. Dust and salt particles act as hygroscopic nuclei around which water vaopur condenses to produce cloud.

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The Energy Balance: The earth atmosphere system is sustained by the supply of energy from the SUN. The transfer of energy from place to place is of major importance in Climatology. There are three ways in which in which this transfer can take place; 1.Conduction: consists of energy transfer directly from molecule to molecule where the molecules are densely packed and contact one another. Energy always moves from an area of more energy to an area of less energy. 2.Convection: involves the transfer of energy by the movement of an energy laden substance from one location to another. This substance may be solid, liquid, or gas. 3.Radiation: is the only means of energy transfer through space without the aid of a material medium

THE SOLAR SOURCE:  The sun is gaseous mass with a diameter 109 times that of Earth. The source of sun’s energy is nuclear fusion produced in the core of the sun, where a nuclear reaction takes place that changes Hydrogen into Helium. Major parts are the Core, Photosphere (visible surface), Chromosphere and Corona.  PHOTOSPHERE: Photosphere is bright outer layer of the sun that emits most of the radiation particularly visible light. Brightness is the result of bursts of extremely hot gases formed in the photosphere. The elements in the photosphere are Hydrogen (90%) and Helium (10%). At the radiative surface, the effective temperature is about 6000°C.

THE ATMOSPHERE AND SOLAR RADIATION:  The energy emitted by the sun passes through space until it strikes some object.  The quantity of radiation is approximately 1367 W/ m. sq. and is known as the SOLAR CONSTANT.  Solar Constant is the basic amount of energy available at the outer limits of Earth’s atmosphere. After this several processes deplete the solar radiation as it passes into the atmosphere. These processes include Reflection, Scattering, Absorption and Transmission.

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1/18/2017

THE NATURE OF RADIATION:  Every object above the temperature of absolute zero -273°C, radiates energy (in the form of electromagnetic waves) to its environment.  Absolute zero is the temperature at which all molecular motion would cease.  The hotter an object is, the greater the flow of energy is from it (Stephan-Boltzmans law)  Another law (Wien’s Law) of radiant energy states the wavelength of maximum radiation is inversely proportional to the absolute temperature (higher the temperature, shorter the wavelength.

 CHROMOSPHERE: Just above the Photosphere is the Chromosphere. It is relatively thin layer of burning Gases. Solar wind and solar flares are produced in this wind.  Sunspots: One of the most prominent visible features of the sun’s surface are dark areas known as Sunspots. Sunspots appear dark because they are about 1500°C cooler than the surrounding Chromosphere.

REFLECTION:  The earth and its atmosphere reflect part of the solar radiation back to space. Reflectivity or Albedo is expressed as a percentage of the incident radiation reaching the surface. Clouds are by far the most important reflectors in the earth environment. Reflectivity ranges from 40 to 90 % depending on type and thickness. Reflectivity of water depends on the angle of the solar beam and the roughness of the water surface. Reflectivity of water decreases as the sun get higher and higher in the sky. When the surface is smooth and sun is near the horizon, reflectivity is high.

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1/18/2017

SCATTERING:  Scattering is the process by which small particles and molecules of gases diffuse part of the radiation in different directions. The process changes the direction of the radiation in a relatively random fashion.  According to Rayleigh Scattering (Rayleigh is name of scientist), the amount and direction of scatter depends on the ratio of the radius of the scattering particle to the wavelength of the energy.  Sky colour depends on the lengths of the path solar radiation takes through the atmosphere. The shortest wavelengths are scattered first. Thus when the radiation is perpendicular to the earth, the sky appears blue. When the sun is low in the sky, the blue is all filtered out and yellow, orange, and red predominate.  Scattering of the full visible spectrum on a hazy day results such that white light seems to come from all directions.

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