Here is a compilation of essays on the ‘Atmosphere’ for class 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on the ‘Atmosphere’ especially written for school and college students.
Essay on Atmosphere
- Essay on the Introduction on Atmosphere
- Essay on the Composition of Atmosphere
- Essay on the Structure of Atmosphere
- Essay on the Physical Properties of Atmosphere
- Essay on the General Circulation of Atmosphere
- Essay on the Role of Atmosphere
Essay # 1. Introduction on Atmosphere:
An atmosphere (atmosphaera,) created in the 17th century from Greek atmos “Vapor” and sphaira “sphere” is a layer of gases that may surround a material body of sufficient mas and that is held in place by the gravity of the body.
Some planets consist mainly of various gases, but only their outer layer is their atmosphere.
Earth’s atmosphere, which contains oxygen used by most organisms for respiration and carbon dioxide used by plants, algae and cyanobacteria for photosynthesis, also protects living organisms from genetic damage by solar ultraviolet radiation. The oxygen so characteristic of our atmosphere was almost all produced by plants (cyanobacteria or, more colloquially, blue-green algae).
The present composition of the atmosphere is 79% nitrogen, 20% oxygen, and 1% other gases including carbon di oxide. The troposphere is where all weather takes place; it is the region of rising and falling packets of air. The air pressure at the top of the troposphere is only 10% of that at sea level 0.1 atmospheres.
The buffer zone between the troposphere and the next layer is called the tropopause. Just above the troposphere there is the stratosphere, where air flow is mostly horizontal. The thin ozone layer is present in the upper stratosphere zone that has a high concentration of ozone, a particularly reactive form of oxygen.
This ozone layer is primarily responsible for absorbing the ultraviolet radiation from the Sun. The formation of this layer is a delicate matter, since only when oxygen is produced in the atmosphere can an ozone layer formation. There is considerable recent concern that man-made fluorocarbon compounds may be depleting the ozone layer, with dire future consequences for life on the Earth.
The mesosphere is above the stratosphere and below the ionosphere (or thermosphere). In ionosphere many atoms are ionized, atoms either gained or lost electrons so they have a net electrical charge. The ionosphere is very thin and is also responsible for absorbing the most energetic photons from the Sun.
The structure of the ionosphere is strongly influenced by the charged particle wind from the Sun. An ore is a rock that contains a valuable or useful metal at a concentration high enough to make its mining a profitable operation.
Essay # 2. Composition of Atmosphere:
Dry air is a mixture of gases with about 78 per cent of nitrogen, 21 per cent of oxygen and 0.94 per cent of argon by volume, and minute quantities of carbon dioxide, helium, neon, krypton, xenon oxides of nitrogen, hydrogen and ozone, and in some localities volatile organic matter, sulphurous gases and chlorine from volcanoes and other sources.
Water vapour is also a part of the atmosphere and is present to about 1.2 per cent of the total volume. Water vapour content depends on temperature and forms about 2.63 per cent at equator, 0.92 per cent at latitude 50° N and 0.22 per cent at latitude 70° N.
At some places the atmosphere may contain considerable amounts of fine earthy, salt crystals, smoke, soot, pollen, bacteria, volcanic dust, meteoric dust etc. spread as impurities to such an extent the sky may appear dark reducing visibility.
Dust present in the atmosphere increases red colours at dawn and twilight. Dust particles and minute salt crystals become nuclei around which water vapour condenses producing cloud particles of water or ice.
The earth has twogreat realms:
(i) Lithosphere (solids),
(ii) Hydrosphere (water) and
The gaseous realm extends over the earth’s surface to a height of about 9,600 km and envelops it. It consists of several gases and minute suspended liquid and solid particles. Air is a mixture of several gases. Four gases: nitrogen, oxygen, argon and carbon dioxide account for more than 99 per cent of the dry air (Table 2.2).
Essay # 3. Structure of Atmosphere:
Earth’s atmosphere can be divided into five major layers. These layers are mainly determined by whether temperature increases or decrease with altitude.
From lowest to highest, these major layers are:
Troposphere begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (56,000 ft) at the equator, with some variation due to weather. Troposphere is mostly heated by transfer of energy from the surface, so on average the lowest part of the troposphere is warmest and temperature decreases with altitude.
This promotes vertical mixing (hence the origin of its name in the Greek word trope, meaning turn or overturn). Troposphere contains roughly 80 per cent of the mass of atmosphere. Tropopause is the boundary between troposphere and stratosphere.
Stratosphere extends from tropopause to about 51 km (32 mi; 170,000 ft). Temperature increases with height, which restricts turbulence and mixing. Stratopause, which is the boundary between stratosphere and mesosphere, typically is at 50 to 55 km (31 to 34 mi; 160,000 to 180,000 ft). Pressure here is 1/1000th sea level. Stratosphere contains much of the total ozone.
Air density is much less here, so that even limited absorption produces a large temperature increase. Temperature increases fairly, generally, with high in summer, with coolest air at equatorial tropopause. Stratosphere is thicker over poles and sometimes does not exist over the equator. Near its outer limit, stratosphere is the greatest concentration of ozone and rare nacreous clouds occasionally appear.
Mesosphere extends from the stratopause to 80-85 km (50-53 mi; 260,000- 280,000 ft). It is the layer where most meteors burn up upon entering the atmosphere. Temperature decreases with height in the mesosphere. Mesopause, the temperature minimum that marks the top of the mesosphere, is the coldest place on earth and has an average temperature around -100°C (-148.0°F; 173.1°K).
Temperature increases with height in the thermosphere from mesopause up to thermopause, then is constant with height. Temperature of this layer can rises to 1,500°C (2.730°F), though the gas molecules are so far apart that temperature in the usual sense is not well defined.
International Space Station orbits in this layer, between 320 and 380 km (200 and 240 mi). Top of thermosphere is the bottom of exosphere, called the exobase. Its height varies with solar activity and ranges from about 350-800 km (220-500 mi; 1,100.000-2,600,000 ft).
The outermost layer of earth’s atmosphere extends from exobase upward. Here the particles are so far apart that they can travel hundreds of km without colliding with one another. Since the particles rarely collide, atmosphere no longer behaves like a fluid. These free moving particles follow ballistic trajectories and may migrate into and out of magnetosphere or solar wind. Exosphere is mainly composed of hydrogen and helium.
Within the five principal layers determined by temperature are several layers determined by other properties.
Ozone layer is contained within the stratosphere. In this layer ozone concentrations are about 2 to 8 parts per million (ppm), which is much higher than in lower atmosphere but still very small compared to the main components of atmosphere.
Ionosphere, part of atmosphere that is ionised by solar radiation, stretches from 50 to 1,000 km (31 to 620 mi; 160,000 to 3,300,000 ft) and typically overlaps both exosphere and thermosphere. It forms the inner edge of magnetosphere. It has practical importance because it influences, for example, radio propagation on the earth. It is responsible for auroras.
Homosphere and heterosphere are defined by whether the atmospheric gases are well mixed. In the homosphere, chemical composition of atmosphere does not depend on molecular weight because gases are mixed by turbulence. Homosphere includes troposphere, stratosphere and mesosphere. Above turbopause at about 100 km (62 mi; 330,000 ft), essentially corresponding to mesopause, the composition varies with altitude.
This is because the distance that particles can move without colliding with one another is large compared with size of motions that cause mixing. This allows the gases to stratify by molecular weight, with the heavier ones such as oxygen and nitrogen present only near the bottom of heterosphere. Upper part of heterosphere is composed almost completely of hydrogen, the lightest element.
Planetary boundary layer is part of troposphere that is nearest to earth’s surface and is directly affected by it, mainly through turbulent diffusion. During the day the planetary boundary layer usually is well mixed, while at night it becomes stably stratified with weak or intermittent mixing. Depth of planetary boundary layer ranges from as little as about 100 m on clear, calm nights to 3000 m or more during afternoon in dry regions.
Average temperature of the atmosphere at the surface of earth is 14°C (57°F; 287°K) or 15°C (59°F: 288° K), depending on the reference.
Essay # 4. Physical Properties of Atmosphere:
i. Pressure and Thickness:
Average atmospheric pressure at sea level is about 1.0 atmosphere (atm) = 101.3 kPa (kilo-Pascals) = 14.7 psi (pounds per square inch) = 760 torr = 29.9 inches of mercury (Hg). Total atmospheric mass is 5.1480 x 1018 kg (1.135 x 1019lb), about 2.5 per cent less than would be inferred from average sea level pressure and earth’s area of 51007.2 mega-hectares, this defect having been displaced by the earth’s mountainous terrain.
Atmospheric pressure is the total weight of air above unit area at the point where pressure is measured. Thus, air pressure varies with location and time, because amount of air above earth’s surface varies.
If atmospheric density were to remain constant with height, atmosphere would terminate abruptly at 8.50 km (27,900 ft). Instead, density decreases with height, dropping by 50 per cent at an altitude of about 5.6 km (18,000 ft).
As a result, pressure decrease is approximately exponential with height, so that pressure decreases by a factor of two approximately every 5.6 km (18,000 ft) and by a factor of e = 2.718… approximately every 7.64 km (25,100 ft), the latter being the average scale height of earth’s atmosphere below 70 km (43 mi; 230,000 ft).
However, because of changes in temperature, average molecular weight and gravity throughout the atmospheric column, the dependence of atmospheric pressure on altitude is modeled by separate equations for each of the layers. Even in the exosphere, atmosphere is still present. This can be seen by the effects of atmospheric drag on satellites.
In summary, the equations of pressure by altitude can be used directly to estimate atmospheric thickness.
However, the following published data are given:
1. 50 per cent of the atmosphere by mass is below an altitude of 5.6 km (18,000 ft).
2. 90 per cent of the atmosphere by mass is below an altitude of 16 km (52,000 ft). The common altitude of commercial airliners is about 10 km (33,000 ft) and Mt Everest’s summit is 8,848 m (29,030 ft) above sea level.
3. 99.99997 per cent of the atmosphere by mass is below 100 km (62 mi; 330,000 ft), although in the rarefied region above this there are auroras and other atmospheric effects. The highest X-15 plane flight in 1963 reached an altitude of 354,300 ft (108.0 km).
ii. Density and Mass:
Density of air at sea level is about 1.2 kg m-3 (1.2 g l-1). Density is not measured directly but is calculated from measurements of temperature, pressure and humidity using the equation of state for air (a form of the ideal gas law). Atmospheric density decreases as altitude increases. This variation can be approximately modeled using the barometric formula. More sophisticated models are used to predict orbital decay of satellites.
Average mass of atmosphere is about 5 quadrillion (5 x 1015) tonnes or 1/1,200,000 the mass of earth.
According to National Center for Atmospheric Research, “total mean mass of atmosphere is 5.1480 x 1018 kg with an annual range due to water vapor of 1.2 or 1.5 x 1015 kg depending on whether surface pressure or water vapor data are used; somewhat smaller than the previous estimate. Mean mass of water vapor is estimated as 1.27 x 1016 kg and dry air mass as 5.1352 ± 0.0003 x 1018 kg.”
iii. Optical Properties:
Solar radiation (sunlight) is the energy earth receives from sun. Earth also emits radiation back into space, but at longer wavelengths that we cannot see. Part of the incoming and emitted radiation is absorbed or reflected by the atmosphere.
When light passes through atmosphere, photons interact with it through scatter. If light does not interact with atmosphere, it is called direct radiation and is what you see if you were to look directly at the sun. Indirect radiation is light that has been scattered in the atmosphere.
For example, on an overcast day when you cannot see your shadow there is no direct radiation reaching you, it has all been scattered. As another example, due to a phenomenon called Rayleigh scattering, shorter (blue) wavelengths scatter more easily than longer (red) wavelengths.
This is why the sky looks blue, you are seeing scattered blue light. This is also why sunsets are red. Because the sun is close to the horizon, sun’s rays pass through more atmosphere than normal to reach your eye. Much of blue light has been scattered out, leaving red light in a sunset.
Different molecules absorb different wavelengths of radiation. For example, O2and O3 absorbs almost all wavelengths shorter than 300 nanometers. Water (H2O) absorbs many wavelengths above 700 nm. When a molecule absorbs a photon, it increases the energy of the molecule. We can think of this as heating the atmosphere, but atmosphere also cools by emitting radiation.
Combined absorption spectra of gasses in the atmosphere leave “windows” of low opacity, allowing transmission of only certain bands of light. Optical window runs from around 300 nm (ultraviolet-C) up into the range humans can see, the visible spectrum (commonly called light), at roughly 400-700 nm and continues to infrared to around 1100 nm. There are also infrared and radio windows that transmit some infrared and radio waves at longer wavelengths. For example, radio window runs from about one centimeter to about eleven-meter waves.
Emission is opposite of absorption, it is when an object emits radiation. Objects tend to emit amounts and wavelengths of radiation depending on their “black body” emission curves, therefore hotter objects tend to emit more radiation, with shorter wavelengths. Colder objects emit less radiation, with longer wavelengths.
For example, sun is approximately 6,000 K (5,730°C; 10,340°F), its radiation peaks near 500 nm and is visible to human eye. Earth is approximately 290 K (17°C; 62°F), so its radiation peaks near 10,000 nm and is much too long to be visible to humans.
Because of its temperature, atmosphere emits infrared radiation. For example, on clear night’s earth’s surface cools down faster than on cloudy nights. This is because clouds (H2O) are strong absorbers and emitters of infrared radiation. This is also why it becomes colder at night at higher elevations. Atmosphere acts as a “blanket” to limit the amount of radiation earth loses into space.
Greenhouse effect is directly related to this absorption and emission (or “blanket”) effect. Some chemicals in the atmosphere absorb and emit infrared radiation, but do not interact with sunlight in the visible spectrum.
Common examples of these chemicals are CO2 and H2O. If there are too much of these greenhouse gasses, sunlight heats the earth’s surface, but gases block the infrared radiation from exiting back to space. This imbalance causes earth to warm and thus climate change.
vii. Refractive Index:
The refractive index of air is close to, but just greater than 1.0. Systematic variations in refractive index can lead to the bending of light rays over long optical paths. One example is that, under some circumstances, observers onboard ships can see other vessels just over the horizon because light is refracted in the same direction as the curvature of the earth’s surface.
Refractive index of air depends on temperature, giving rise to refraction effects when the temperature gradient is large. An example of such effects is the mirage.
Atmospheric circulation is large scale movement of air and the means (with ocean circulation) by which heat is distributed around the earth. Large scale structure of atmospheric circulation varies from year to year, but the basic structure remains fairly constant as it is determined by earth’s rotation rate and difference in solar radiation between equator and poles.
Essay # 5. General Circulation of Atmosphere:
The worldwide system of winds, which transports warm air from the equator where solar heating is greatest towards the higher latitudes, is called the general circulation of the atmosphere, and it gives rise to the Earth’s climate zones.
The general circulation of air is broken up into a number of cells, the most common of which is called the Hadley cell. Sunlight is strongest nearer the equator. Air heated there rises and spreads out north and south. After cooling the air sinks back to the Earth’s surface within the subtropical climate zone between latitudes 25° and 40°.
This cool descending air stabilises the atmosphere, preventing much cloud formation and rainfall. Consequently, many of the world’s desert climates can be found in the subtropical climate zone. Surface air from subtropical regions returns towards the equator to replace the rising air, so completing the cycle of air circulation within the Hadley cell.
Although the physical reality of Hadley Cells has been questioned, they provide an excellent means for describing the way in which heat is transported across the Earth by the movement of air. Other circulation cells exist in the mid-latitudes and polar-regions. The general circulation serves to transport heat energy from warm equatorial regions to colder temperate and polar regions. Without such latitudinal redistribution of heat, the equator would be much hotter than it is whilst the poles would be much colder.
Without the Earth’s rotation, air would flow north and south directly across the temperature difference between low and high latitudes. The effect of the Coriolis force as a consequence of the Earth’s rotation however, is to cause winds to swing to their right in the Northern Hemisphere, and to their left in the Southern Hemisphere. Thus the movement of air towards the equator swings to form the northeast and southeast trade winds of tropical regions.
Air flowing towards the poles forms the westerlies associated with the belt of cyclonic low pressure systems at about 50° to 60° north and south. In general, where air is found to descend, high pressure develops, for example at the subtropical latitudes and again near the poles. Where air is rising, atmospheric pressure is low, as at the equator and in the mid-latitudes where storms or frontal systems develop.
Essay # 6. Role of Atmosphere:
i. Air functions as a medium for locomotion of insects, birds etc.
ii. Ozone layer of atmosphere protects the living organisms from harmful radiations of sun.
iii. Air is the source of oxygen, carbon dioxide and nitrogen required for various metabolic activities of living beings.
iv. It helps in dispersal of spores, pollen, seeds etc.
v. Air maintains temperature on earth required for life.
vi. Air transmits sound for communication.
vii. Ionosphere reflects the radio waves back to earth for long distance communication due to presence of ions and free electrons in this zone.
viii. Burning of fire takes place in presence of oxygen.
ix. Specie climatic conditions and water cycle is maintained due to circulation of air.