Introduction to Constitution & Preamble | 1 GEOGRAPHY MASTER SERIES UNIT 1 Climatology The ‘Atmosphere’ Around Us What is Climatology? ● It is due to the atmosphere that living beings can perform photosynthesis and respiration Climatology is the study of the atmospheric conditions and related climate & weather phenomena. which is essential part of survival of all life on the Earth. The Earth has a radius of 6400 km, and possesses a ● As part of the hydrologic cycle, water spends narrow skin called atmosphere which is the air that a lot of time in the atmosphere, mostly as envelopes the earth which stretches upwards upto a water vapour. The atmosphere is an important maximum thickness of about 500 km. Ninety-nine per reservoir for water. cent of the gases that constitute the atmosphere, are ● Ozone in the upper atmosphere absorbs high- located below a height of 32 km. energy ultraviolet (UV) radiations coming Earth’s atmosphere protects us from incoming space from the Sun. This protects living beings debris like comets, asteroids that burn up before on the Earth’s surface from the Sun’s most reaching the planet’s surface, and blocks harmful harmful rays. short wavelength radiations from the Sun. The lower ● Along with the oceans, the atmosphere keeps boundary of the atmosphere is considered to lie on the Earth’s temperatures within an acceptable Earth’s surface, the upper boundary is the gradational range. Without an atmosphere, Earth’s transition into space. temperatures would be frigid at night and It blocks the outgoing long wave radiations to keep the scorching hot during the day. Earth from cooling to below freezing temperatures, ● The atmosphere also takes care of extra- thus creating greenhouse effect, which is essential for terrestrial objects like meteors, which get burnt the life over the Earth surface. up while passing through the atmosphere due The weather we experience at the land surface is to the friction. largely determined by the interaction of different ● Weather is another important phenomenon wavelengths of incoming solar radiations with the which dictates the direction of a number of atmosphere. The solar radiation supplies the energy natural and man-made processes, like plant necessary for cloud formation, precipitation, and local growth, agriculture, soil-formation, human weather conditions. settlements, etc. Various climatic factors join together to create weather patterns. ‘Utility’ of The Earth Composition of Our ● All living beings need some of the gases in air for their life support. Without an atmosphere, Atmosphere the Earth would be just some another lifeless The atmosphere is composed of a mix of several rock. different gases in differing amounts. 2 Master Series : Geography The permanent gases whose percentages do not ● As the atmosphere is shallow, its motions over change from day to day are nitrogen, oxygen and large areas are primarily horizontal. argon. ● The horizontal wind speeds are many times greater than the vertical wind speeds, but the small vertical Composition of Gases in the Atmosphere displacements of air have significant impact upon Gases Amount in Percentage the state of our atmosphere. Nitrogen 78.1 Oxygen 20.9 Aerosols: The Suspended Dust Particles Carbon Dioxide 0.9 in Atmosphere Hydrogen 0.03 ● With all the gases, the atmosphere contains a wide Neon 0.01 variety of suspended articles, known collectively as Helium 0.0018 aerosols. Ozone 0.0005 ● Aerosols may be liquid or solid and are small enough that they may require very long time to Others 0.00006 settle out of the atmosphere by gravity. ● It occurs up to 120 km but up to Oxygen: ● Common aerosols include suspended soil or desert 6 km as O2 forms or as unstable ozone while sand particles, smoke particles from wildfires, above it occurs in dissociated. It amount to salt particles from evapourated ocean water, plant 20.95%. pollen, volcanic dust, and particles formed from the ● Nitrogen: Accounts for 78% of the pollution created by coal burning power plants. atmosphere. ● Aerosols significantly affect atmospheric heat ● Gases like carbon dioxide, nitrous oxides, balance, cloud growth, and optical properties. methane, and ozone are trace gases that ● The particles in aerosols cover a wide range of sizes. account for about a tenth of one per cent of Raindrops in clouds are 1-6 mm in diameter. Fine the atmosphere. desert sand and cloud droplets range in diameter down to about 0.01 mm. Sea salt particles and ● It is unique as its Water Vapour: smoke particles are 1/100th of this, about 0.0001 concentration varies from 0-4% of the mm, or 0.1 micrometre, in diameter (1 micrometre atmosphere depending on location and time of = one thousandth of a millimetre). the day. In the cold, dry arctic regions, water ● Smallest of all aerosols are the particles that form vapour usually accounts for less than 1% of the when certain gases condense—that is, when several atmosphere, while in humid, tropical regions gas molecules come together to form a stable cluster. water vapour can account for almost 4% of These are the Aitkin nuclei, whose diameters can be the atmosphere. Water vapour content is very measured down to a few nanometers (1 nanometre important in predicting the weather. It contains = one millionth of a millimetre). huge numbers of solid and liquid particles, ● The size of some aerosol particles allows them to collectively called ‘aerosols’ or the particulate efficiently scatter sunlight and create atmospheric matter. Most of the solid particles are kept in haze. suspension in the atmosphere. These particulate ● Under some conditions, aerosols act as collecting materials help in scattering the solar incoming points for water vapour molecules, encouraging the radiation which lead to the sunset and sunrise growth of cloud droplets and speeding the formation colour appearance over the horizon. of clouds. ● Aerosols may also play a role in Earth’s climate. Facts Related to Atmosphere ● Aerosols are known to reflect a portion of incoming ● Most of the atmospheric mass is confined in the solar radiation back to space, which lowers the lowest 100 km above the sea-level. temperature of Earth’s surface. Cont... Climatology 3 The Past, Present and Future ● Now, over billions of years, a considerable excess “Atmosphere” built up this way, so that oxygen now makes up over ● At the time of formation of the Earth, 4.5 billion 20% of the atmosphere (and carbon dioxide makes years ago, the present atmosphere was not there, it up less than 0.033%). was just like those of other planets. ● It is difficult to predict the future changes to the ● The atmosphere of the Earth that was present after atmosphere. Earth was formed about 4.5 billion years ago was ● It is now argued that the human activity may be probably much different than that of today, with altering the atmosphere to the point that it may abundance of gases like hydrogen, ammonia and affect Earth’s climate. methane. Layers of Atmosphere ● The Earth at the beginning would had just resembled those of the outer planets—Jupiter, Saturn, Uranus, Earth’s atmosphere is divided into five main layers. and Neptune—with an abundance of hydrogen, The exosphere, the thermosphere, the mesosphere, methane, and ammonia gases. the stratosphere and the troposphere. There is ● The present atmosphere did not form until after this no distinct boundary between the atmosphere and primary atmosphere was lost. space, but an imaginary line about 62 miles (100 ● Probably, the primary atmosphere was blasted from kilometres) from the surface, called the Karman line, Earth by the Sun. If the Sun is like other stars of is usually where scientists say atmosphere meets the its type, it may have gone through a phase where outer space. (Ref. Fig 1. 1) it violently ejected material outward toward the planets. All of the inner planets, including Earth, (a) The Troposphere: It is the layer closest would have lost their gaseous envelopes. to Earth’s surface. It is 8 to 18 km thick near ● A secondary atmosphere began to form when gases poles and equator, and contains half of Earth’s were released from the crust of the early Earth atmosphere. Air is warmer near the ground by volcanic activity. These gases included water and gets colder higher up. Nearly all of the vapour, carbon dioxide, nitrogen, and sulfur or water vapour and dust in the atmosphere are sulfur compounds. in this layer that is why clouds are found here. ● Oxygen was absent from this early secondary atmosphere. Within the troposphere, temperature decreases ● The large amount of water vapor released by the with altitude at a rate of about 6.5° C per volcanoes formed clouds that continually rained on kilometre. The boundary between troposphere the early Earth, forming the oceans. and the overlying stratosphere is known as the ● As carbon dioxide dissolves easily in water, the new tropopause and temperatures at this altitude oceans gradually absorbed most of it. typically approach –50°C. ● Nitrogen, being unreactive, was left behind to (b) The Stratosphere: It is the second layer of become the most common gas in the atmosphere. atmosphere. It starts above the troposphere and ● The carbon dioxide that remained began to be used by early plant life in the process of photosynthesis ends about (12-50 km) above ground. Ozone is two to three billion years ago, probably in an ocean abundant here and it heats up the atmosphere or aquatic environment. while also absorbing harmful ultraviolet (UV) ● At that time, there appeared aerobic (oxygen using) radiation from the Sun creating very stable bacteria and other early animal life, which consumed atmospheric conditions. The air here is very dry, the products of photosynthesis and emitted CO2. and it is about a thousand times thinner here than ● The cycles for CO2 and O2 were completed; the two gases stayed in balance as all plant material at sea level.