Climatology PDF

=> - ⑭ WHAT IS THE ATMOSPHERE? The envelope of gases surrounding the earth is called the atmosphere. It forms a protective boundary between the outer space and the biosphere. The atmosphere is a dynamic collection of gases that constantly move and c...

=> - ⑭ WHAT IS THE ATMOSPHERE? The envelope of gases surrounding the earth is called the atmosphere. It forms a protective boundary between the outer space and the biosphere. The atmosphere is a dynamic collection of gases that constantly move and change. These gases form several layers around Earth that are loosely defined by composition and temperature. The gases of the present atmosphere are not the direct residue of the early stage of earth’s formation. They are a product of progress through volcanic eruptions, hot springs, chemical breakdowns of solid matter and redistribution from the biosphere. The atmosphere is a significant component of the biospheric ecosystem because life on the earth’s surface is because of this atmosphere otherwise the earth would have become barren like the moon. It protects the earth from the harmful radiation from the sun. It acts as a greenhouse by allowing short-wave radiation (from Sun) and trapping long-wave terrestrial radiation (from Earth’s surface). All life forms need a particular range of temperature and a specific range of frequencies of solar radiation to carry out their biophysical processes. The atmosphere absorbs certain frequencies and lets through some other frequencies of solar radiation. In other words, the atmosphere regulates the entry of solar radiation. The atmosphere also keeps the temperature over the earth’s surface within certain limits. In the absence of the atmosphere extremes of temperature would exist between day and night over the earth’s surface. The atmosphere also takes care of extra-terrestrial objects like meteors that get burnt up while passing through the atmosphere (mesosphere to be precise) due to friction. Prelims USP (Geography) by Vikas Ahlawat Sir & Team - > ⑬ COMPOSITION OF THE ATMOSPHERE The gases in the atmosphere are composed of neutral, uncharged particles. Except for the noble gases, atoms in the gas phase share electrons with other atoms in chemical bonds so that their electron count can approach the more stable filled-shell configuration. The Earth’s atmosphere consists of a mixture of noble gas atoms and many kinds of molecules. The atmosphere is composed of – Gases Vapour Particulates In addition, it contains huge numbers of solid and liquid particles, collectively called aerosols. meet Prelims USP (Geography) by Vikas Ahlawat Sir & Team # GASES Nitrogen and oxygen make up nearly 99% of the clean, dry air. The remaining gases are mostly inert and constitute about 1% of the atmosphere. Oxygen, although constituting only 21% of the total volume of the atmosphere, is the most important component among gases. All living organisms inhale oxygen. Besides, oxygen can combine with other elements to form important compounds, such as oxides. Also, combustion is not possible without oxygen. Nitrogen accounts for 78% of total atmospheric volume. It is a relatively inert gas and is an important constituent of all organic compounds. The main function of nitrogen is to control combustion by diluting oxygen. It also indirectly helps in the oxidation of different kinds. Carbon Dioxide which constitutes only about 0.038% of the dry air and is a product of combustion. Green plants, through photosynthesis, absorb carbon dioxide from the atmosphere and use it to manufacture food and keep other biophysical processes going. Being an efficient absorber of heat, carbon dioxide is considered to be of great climatic significance. Carbon dioxide is considered to be a very important factor in the heat energy budget. With the increased burning of fossil fuels – oil, coal, and natural gas – the carbon dioxide percentage in the atmosphere has been increasing at an alarming rate. More carbon dioxide in the atmosphere means more heat absorption. This could significantly raise the temperature at lower levels of the atmosphere thus inducing drastic climatic changes. Carbon dioxide and water vapour are found only up to 90 km from the surface of the earth. Prelims USP (Geography) by Vikas Ahlawat Sir & Team ⑬ The third important gas is Argon which constitutes only about 0.93%. Ozone (03) is another important gas in the atmosphere, which is actually a type of oxygen molecule consisting of three, instead of two, atoms. It forms less than 0.00006% by volume of the atmosphere and is unevenly distributed. It is between 20 km and 25 km altitude that the greatest concentrations of ozone are found. It is formed at higher altitudes and transported downwards. Ozone plays a crucial role in blocking the harmful ultraviolet radiation from the sun. Other gases found in almost negligible quantities in the atmosphere are neon, helium, hydrogen, xenon, krypton, methane, etc. Water Vapour The vapour content in the atmosphere ranges from 0 to 5 % by volume. The atmospheric vapour is received through the evaporation of moisture and water from the water bodies (like seas and oceans, lakes, tanks and ponds, rivers, etc.), vegetation, and soil cover. Vapour depends on temperature and therefore it decreases from the equator poleward in response to decreasing temperature towards the poles. = Prelims USP (Geography) by Vikas Ahlawat Sir & Team e The content of the vapour in the surface air in the moist tropical areas, at 50-degree and 70-degree latitudes, is 2.6%, 0.9%, and 0.2% (by volume) respectively. The content of vapour decreases upward. More than 90% of the total atmospheric vapour is found up to the height of 5 km. The moisture content in the atmosphere creates several forms of condensation and precipitation e.g. clouds, fogs, dew, rainfall, frost, hailstorm, ice, snowfall, etc. Vapour is almost transparent for incoming shortwave solar radiation so that the electromagnetic radiation waves reach the earth’s surface without many obstacles but vapour is less transparent for outgoing longwave terrestrial radiation and therefore it helps in heating the earth’s surface and lower portion of the atmosphere because it absorbs terrestrial radiation. see nee Prelims USP (Geography) by Vikas Ahlawat Sir & Team = e PARTICULATE MATTER The Solid Particles present in the atmosphere consist of sand particles (from weathered rocks and also derived from volcanic ash), pollen grains, small organisms, soot, ocean salts; the upper layers of the atmosphere may even have fragments of meteors which got burnt up in the atmosphere. These particulates help in the absorbing, reflecting, and scattering of the solar radiation which adds the varied charming color of red and orange at sunrise and sunset. The sky appears blue in color due to the selective scattering of solar radiation by dust particles. Salt particles become hygroscopic nuclei and thus help in the formation of water drops, clouds, and various forms of condensation and precipitation. Hygroscopic nucleus – a microscopic particle (e.g. of sulphur dioxide, salt, dust, or smoke) in the free air, on to which water vapor may condense to form droplets. Prelims USP (Geography) by Vikas Ahlawat Sir & Team - The atmosphere can be divided into different layers according to composition, density, pressure, and temperature variations. Based on Composition: According to its composition, broadly it is divided into two layers- 1. homosphere 2. heterosphere Homosphere The homosphere is the lower segment of the two-part division of atmosphere and further consists of three regions namely troposphere, stratosphere and mesosphere. The Troposphere is the earth’s weather layer. It contains nearly all weather conditions. As you go up in altitude the temperature goes down. It is the bottom-most layer of the The Stratosphere is the middle region of the Homosphere. The Mesosphere is the top layer of the Homosphere. All the three regions have the same composition of air. However, the concentration of air keeps decreasing significantly as the altitude increases. It extends from the earth’s surface up to an altitude of 80km. Prelims USP (Geography) by Vikasse These Ahlawat Sir & Team t HETEROSPHERE The heterosphere is the layer of an atmosphere where the gases are separated out by molecular diffusion with increasing altitude such that lighter species become more abundant relative to heavier species. In the Heterosphere, there are two regions: The Thermosphere and the Exosphere. These two regions are considered outer space. The thermosphere is the bottom region of the Heterosphere. The exosphere is the top region of the Heterosphere. It begins over 80km and extends up to 10,000 km. teeeeee Prelims USP (Geography) by Vikas Ahlawat Sir & Team m BASED ON CHANGE IN TEMPERATURE The atmosphere can be divided into five layers according to the diversity of temperature and density. They are: Troposphere Stratosphere Mesosphere Thermosphere (Ionosphere) Exosphere = # Prelims PrelimsUSP => USP(Geography) (Geography)by byVikas VikasAhlawat AhlawatSir Sir&&Team Team ⑪ TROPOSPHERE The troposphere is the lowest layer of Earth’s atmosphere. It extends up to 18km at the equator, 13 km at mid-latitude and about 8km at poles. Most of the mass (about 75-80%) of the atmosphere is in the troposphere. The thickness is greater at the equator, because the heated air rises to greater heights. The troposphere ends with the Tropopause. The temperature in this layer, as one goes upwards, falls at the rate of 5°C per kilometer, and reaches -45°C at the poles and -80°C over the equator at Tropopause (greater fall in temperature above equator is because of the greater thickness of troposphere – 18 km). The fall in temperature is called ‘lapse rate’. The troposphere is marked by temperature inversion, turbulence and eddies. It is also meteorologically the most significant zone in the entire atmosphere (Almost all the weather phenomena like rainfall, fog and hailstorm etc. are confined to this layer). It is also called the convective region, since all convection stops at Tropopause. The troposphere is the theatre for weather because all cyclones, anticyclones, storms and precipitation occur here, as all water vapors and solid particles lie within this. The troposphere is influenced by seasons and jet streams. meeeeeeeeeeeeeeeeeeeeeeeeeeee Prelims USP (Geography) by Vikas Ahlawat Sir & Team - TROPOPAUSE The tropopause is the atmospheric boundary that demarcates the troposphere from the stratosphere. This layer is marked by constant temperatures. Stratosphere It lies above the troposphere and extends uniformly across the globe up to 50km. The temperature in this layer remains constant for some distance but then rises to reach a level of 0°C at 50 km altitude. This rise is due to the presence of ozone (harmful ultraviolet radiation is absorbed by ozone). This layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aero planes. So aero planes fly in lower stratosphere, sometimes in upper troposphere where weather is calm. Sometimes, cirrus clouds are present at lower levels in this layer. Prelims USP (Geography) by Vikas Ahlawat Sir & Team # MESOSPHERE The mesosphere extends from 50 – 80 km. The temperature again decreases in this layer and reaches its minimum mark averaging -90 C. Although this temperature can vary. The homogenous layer extends up to the mesosphere. At the upper boundary of the mesosphere, there exists a layer of ions extending in the other layer. This layer of ions or charged particles is helpful in reflecting the radio waves and helps in telecommunication. see e Prelims USP (Geography) by Vikas Ahlawat Sir & Team # THERMOSPHERE In thermosphere temperature rises very rapidly with increasing height. Ionosphere is a part of this layer. It extends between 80-400 km. This layer helps in radio transmission. In fact, radio waves transmitted from the earth are reflected back to the earth by this layer. Person would not feel warm because of the thermosphere’s extremely low pressure. The International Space Station and satellites orbit in this layer. (Though temperature is high, the atmosphere is extremely rarified – gas molecules are spaced hundreds of kilometers apart. Hence a person or an object in this layer doesn’t feel the heat) Aurora’s are observed in lower parts of this layer. Prelims USP (Geography) by Vikas Ahlawat Sir & Team · IONOSPHERE This layer is located between 80 km and 400 km and is an electrically charged layer. It lies from the upper mesosphere to the thermosphere. The charged particles are ionized by absorption of cosmic rays, gamma rays, X-rays and shorter wavelengths of ultraviolet rays. It is in this layer that incoming space vehicles and meteorites begin to heat due to friction. Temperature again starts increasing with height because of radiation from the sun. meeeeeeeeeeee Prelims USP (Geography) by Vikas Ahlawat Sir & Team a EXOSPHERE This is the uppermost layer of the atmosphere extending beyond the ionosphere above a height of about 400 km. The air is extremely rarefied and the temperature gradually increases through the layer. Light gases like helium and hydrogen float into the space from here. Temperature gradually increases through the layer. (As it is exposed to direct sunlight) This layer coincides with space. Prelims USP (Geography) by Vikas Ahlawat Sir & Team = Ap # INSOLATION (OR INCOMING SOLAR RADIATION) Insolation is the amount of solar radiation that is received by a planet. The energy received by the earth’s surface in the form of short waves is termed as Incoming Solar Radiation or Insolation. The insolation is not constant over the surface of the Earth — it is concentrated near the equator because of the curvature of the Earth. Some of the insolation is reflected off the atmosphere back out into space, where it is lost. The remaining insolation may pass through the atmosphere, where it can be transformed either before or after reaching Earth’s surface. This reception of solar energy and the resulting energy cascade that ultimately warms Earth’s surface and the atmosphere. Prelims USP (Geography) by Vikas Ahlawat Sir & Team  VARIABILITY OF INSOLATION AT THE D SURFACE OF THE EARTH The amount and intensity of solar radiation received by the earth (insolation) vary during a day, in a season and in a year. The following are the factors that cause these variations: The rotation of the earth on its axis. The angle of inclination of the rays of the sun The length of the day. The transparency of the atmosphere, and The configuration of the land in terms of its aspect. (The insolation depends more on the first three factors) Prelims USP (Geography) by Vikas Ahlawat Sir & Team · & The tilted position of the earth’s axis is known as the inclination of the earth’s axis. The earth’s rotation axis makes an angle of about 66.5° with the plane of its orbit around the sun and this greatly influences the amount of insolation received at different places. The amount of insolation also depends on the angle of inclination of the sun’s rays. The higher the latitude the less is the angle they make with the surface of the earth which results in slant sun rays. The slant rays cover more area than the vertical rays. When more area is covered, the energy gets distributed and the net energy received per area decreases. Also, the slant rays have to pass through a greater depth of the atmosphere which results in more absorption, diffusion and scattering. Before striking the earth’s surface, the incoming solar radiation passes through the atmosphere. The atmosphere is largely transparent to shortwave solar radiation. Water vapors, ozone and other gases present in the atmosphere absorb most of the near- infrared radiations. Small suspended particles in the troposphere scatter the visible spectrum both to space and towards the surface of the earth. The blue colour of the sky and the red color of the rising and setting sun are the results of the scattering of light within the atmosphere. mn Prelims USP (Geography) by Vikas Ahlawat Sir & Team o ⑭ Duration of the day varies from place to place and season to season. It decides the amount of insolation received on the earth’s surface. The amount of solar radiation received at the surface of the earth is more in the tropics (about 320 watts/m²) and least in the poles (70 watts/m²). The subtropical deserts receive maximum insolation as the atmosphere is more transparent (least cloudiness). At the same latitude, the insolation is more over the continents than over the oceans. TERRESTRIAL RADIATION, HEATING AND COOLING OF THE ATMOSPHERE Terrestrial Radiation – The solar radiation received by the earth is in short wave forms and it heats up its surface. The earth acts as a radiating body and radiates energy in the form of long waves to the atmosphere. This process is called terrestrial radiation and these long wave radiations heat up the atmosphere from below. The atmosphere in turn radiates and transmits heat to space. This maintains the constant temperature at the earth’s surface, as the amount of heat received from the sun is transmitted to space. Prelims USP (Geography) by Vikas Ahlawat Sir & Team · Heating and cooling of the atmosphere (conduction, convection and advection): The terrestrial radiation heats up the lower atmosphere which is directly in contact with the surface of the earth. This process is called conduction in which there is a flow of energy from the warmer to the cooler body and the transfer continues till both the bodies attain the same temperature. As the lower layer of the atmosphere heats up, it rises vertically in the form of currents and transmits the heat of the atmosphere. This vertical heating of the atmosphere is called convection and is restricted only to the troposphere. The transfer of heat through the horizontal movement of air is called advection. During summer in India, the local winds called loo is the outcome of the advection process. Advection is relatively more important than convection. In middle latitude, most of the diurnal (day and night) changes are the result of advection alone. Prelims USP (Geography) by Vikas Ahlawat Sir & Team a HEAT BUDGET OF THE EARTH The surface of the earth maintains its temperature, this is because the amount of heat received by the earth in the form of insolation equals the amount of heat lost by the earth through terrestrial radiation. When 100% of solar radiation reaches the earth’s atmosphere, about 35% is reflected back to space even before reaching the surface of the earth. The reflected amount is called the albedo of the earth. This amount of energy does not heat either the earth or the atmosphere. Out of the remaining 65% of the energy, 14% are absorbed by the atmosphere and the rest, 51% by the surface of the earth (34% through direct solar radiation and 17% from scattered radiation). 51% of the energy received by the earth is radiated back as terrestrial radiation. 17% is radiated back to space directly and the remaining 34% is absorbed by the atmosphere (6% is absorbed directly by the atmosphere, 9% through convection and 19% through latent heat of condensation). The total 48% absorbed by the atmosphere (14% from insolation and 34% from terrestrial radiation) are also radiated back to space. Thus, the total radiation returning back from the atmosphere and the earth is respectively 48+17=65% which balances the total of 65% received from the sun. This is termed the heat balance or heat budget of the earth, and explains how the earth maintains its temperature despite the huge transfer of heat. Prelims USP (Geography) by Vikas Ahlawat Sir & Team  VARIATION IN THE NET HEAT BUDGET AT m THE SURFACE OF THE EARTH The insolation received at the surface varies from place to place, some part of the earth has surplus radiation balance while the other part is deficit. There is a surplus of net radiation balance between 40°N and 40°S and the regions near the poles are in deficit. The extra heat energy from the tropics gets redistributed towards the poles, and as a result, the tropics don’t get progressively heated up due to the accumulation of excess heat nor do the high altitudes get permanently frozen due to excess deficit. Prelims USP (Geography) by Vikas Ahlawat Sir & Team m FACTORS CONTROLLING TEMPERATURE DISTRIBUTION The temperature at any place is influenced by the following factors: Latitude of the place – The temperature of a place depends upon the solar radiation received. The insolation varies according to the latitude, so the temperature also varies accordingly. The solar radiations pass vertically along the equator. The angle of incidence decreases from the equator towards the poles. The area heated by the solar radiation increases towards the poles, therefore temperature decreases from the equator to the poles. Altitude of the place – The terrestrial radiation heats up the atmosphere from below. Hence, the places near the sea level have a higher temperature than the places at higher altitudes. Generally, temperature decreases with the increase in height. The vertical decrease in temperature of the troposphere is called the “normal lapse rate” or “vertical temperature gradient”. The temperature reduces at the rate of 6.5°C per km of ascent. Prelims USP (Geography) by Vikas Ahlawat Sir & Team · Distance from the sea – The location of a place with respect to the sea also influences the temperature of a place. The variation of temperature over the sea is less compared to the land because the land heats up and cools down quickly, while the sea gets heated up slowly and also loses heat slowly. The places near the sea come under the moderating influence of the sea and land breezes which moderate the temperature. Air mass and ocean currents – The places which come under the influence of warm air masses experience higher temperatures and the places that come under the influence of cold air masses experience low temperatures. The places located on the coast where the warm ocean currents flow experience higher temperatures than the places located on the coast where the cold currents flow. *Prelims USP (Geography) > by Vikas Ahlawat Sir & Team =>  & TEMPERATURE BELTS, FACTORS AFFECTING TEMPERATURE e DISTRIBUTION, MEAN AND ANNUAL TEMPERATURE Torrid Zone (Tropical Zone) This is the hottest zone of the Earth. The region that lies from the Tropic of Cancer (23.5°N), across Equator (0°) to the Tropic of Capricorn (23.5°S) is considered the torrid zone (Tropical Zone). The Sun’s ray falls directly at least once a year. Temperate Zone This is the habitable heat zone of the Earth. There are two temperate zones lie in between in both 23½° to 66½° the hemisphere. These regions have moderate, tolerable temperatures. Frigid Zone This is the coldest zone of the Earth. This area lies to the north of the Arctic circle (66.6°N) and to the south of the Antarctic circle (66.5°S) and is permanently frozen. There is no sunlight for most of the months is of the year in this zone. Prelims USP (Geography) by Vikas Ahlawat Sir & Team - FACTORS AFFECTING TEMPERATURE Latitude PATTERNS ON THE GLOBE Temperature Are Higher at Or Near the Equator If Away (North & South Pole) from the Equator – Temperature is Lower. Reasons- For this is the surface of the earth’s part is curved. As a result, the sun ‘s vertical ray strikes different parts of the earth surface at different angles. at the equator, the vertical rays hit the earth’s surface at an angle of 90 (angle of incidence) towards the poles. Land-Sea Differential The albedo of land is much greater than the albedo of oceans and water bodies. Especially snow-covered areas reflect up to 70%-90% of insolation. The average penetration of sunlight is more in water – up to 20 meters than inland – where it is up to 1 meter only. Therefore, the land cools or becomes hot more rapidly compared to oceans. In oceans, continuous convection cycle helps in heat exchange between layers keeping diurnal and annual temperature ranges low. # Prelims USP (Geography) by Vikas Ahlawat Sir & Team · TRANSPARENCY OF ATMOSPHERE Aerosols (smoke, soot), dust, water vapor, clouds, etc. affect transparency. If the wavelength (X) of the radiation is more than the radius of the obstructing particle (such as a gas), then a scattering of radiation takes place. If the wavelength is less than the obstructing particle (such as a dust particle), then total reflection takes place. Absorption of solar radiation takes place if the obstructing particles happen to be water vapor, ozone molecules, carbon dioxide molecules, or clouds. Most of the light received by earth is scattered light. Prelims USP (Geography) by Vikas Ahlawat Sir & Team ⑪ EARTH’S DISTANCE FORM SUN During its revolution around the sun, the earth is farthest from the sun (152 million km on 4th July). This position of the earth is called aphelion. On 3rd January, the earth is the nearest to the sun (147 million km). This position is called the perihelion. Therefore, the annual insolation received by the earth on 3rd January is slightly more than the amount received on 4th July. However, the effect of this variation in the solar output is masked by other factors like the distribution of land and sea and the atmospheric circulation. Hence, this variation in solar output does not have a great effect on daily weather changes on the surface of the earth. Prelims USP (Geography) by Vikas Ahlawat Sir & Team e ALTITUDE altitude is the height above the sea level high altitude (at the mountain), low temperature low altitude (on the land surface), high temperature Reasons at the higher altitudes, the amount of atmosphere decreases and as a result, there is less water vapour in the air. the atmosphere absorbs less heat and therefore the temperature at higher altitude drops. = Prelims USP (Geography) by Vikas Ahlawat Sir & Team · Distance from the Sea the difference in heating of land and water affects the temperature of places located near the coast differently from those located inland. Maritime Influence when the sea is cooler than the land in summer, it lowers the temperature of the coastal place. however, during the winter the sea is warmer than the land and keeps coastal places warmer by moderating the winter temperature. Continental Influence located in the interior of large continents or landmasses are under the continental influence, that is, the sea does not an effect on them as they are too far in temperatures. as the land heats up rapidly, inland locations tend to have hotter summers than areas near the coast in similar latitudes. Ocean Currents ocean currents are large streams of water flowing in the oceans. these generated when winds blow over the water surface. There are two types of ocean currents. cold currents that bring water from the polar regions warm currents that bring warm water to the polar regions ocean currents can raise or lower the temperature of the nearby coastal areas. the coastal area which affected by warm currents will be kept warm during winter if the cold currents move along the coast, they will lower the temperatures of the area. - Prelims USP (Geography) by Vikas Ahlawat Sir & Team Pu Types of land surface Dense forest– the vegetation prevents solar radiation from reaching the ground directly. The ground remains cool. In the city– the presence of concrete surfaces tends to keep the air temperature high. The concrete surface absorbs heat during the day and retains the heat at night. Aspect Aspect is the direction in which a slope faces in relation to the sun. In tropical areas the aspect is not much important because the sun is high in the sky during mid-day. In the temperate areas, the sun is the low angle in winter, this will affect the temperature of slopes that face north to south. In the northern hemisphere, the south-facing slope receive greater concentration of solar radiation and usually warmer than the north-facing slope. Prelims USP (Geography) by Vikas Ahlawat Sir & Team ⑪ e GENERAL TEMPERATURE DISTRIBUTION The highest temperatures occur over tropics and sub-tropics (high insolation). The lowest temperatures occur in polar and subpolar regions. in continents due to the effect of continentality. The diurnal and annual range of temperatures is highest in the interiors of continents due to the effect of continentality (in continental interiors there will no moderating effect of oceans). The diurnal and annual range of temperatures are least in oceans. [high specific heat of water and mixing of water keep the range low] Low-temperature gradients are observed over tropics (the sun is almost overhead the entire year) and high-temperature gradients over middle and higher latitudes (the sun’s apparent path varies significantly from season to season). Temperature gradients are usually low over the eastern margins of continents. (This is because of warm ocean currents) Temperature gradients are usually high over the western margins of continents. (This is because of cold ocean currents) The isotherms are irregular over the northern hemisphere due to an enhanced land-sea contrast. Because of the predominance of land over water in the north, the northern hemisphere is warmer. The thermal equator (ITCZ) lies generally to the north of the geographical equator. While passing through an area with warm ocean currents, the isotherms show a poleward shift. (North Atlantic Drift and Gulf Stream combined with westerlies in Northern Atlantic; Kuroshio Current and North Pacific current combined with westerlies in Northern Pacific) (we will see about ocean currents in detail later.) Mountains also affect the horizontal distribution of temperature. For instance, the Rockies and the Andes stop the oceanic influence from going inwards into North and South America. it Prelims USP (Geography) by Vikas Ahlawat Sir & Team - VERTICAL DISTRIBUTION OF TEMPERATURE The normal, lapse rate is uniform at a given level at all altitudes within the troposphere. At the Tropopause, the lapse rate stops at zero i.e. there is no change in temperature there. In the lower stratosphere, the lapse rate remains constant for some height, while higher temperatures exist over the poles because this layer is closer to earth at the poles. Temperature Anomaly The difference between the mean temperature of a place and the mean temperature of its parallel (latitude) is called the temperature anomaly or thermal anomaly. The largest anomalies occur in the northern hemisphere and the smallest in the southern hemisphere. mee = Prelims D USP (Geography) by Vikas Ahlawat Sir & Team # The thermal equator is a global isotherm having the highest mean annual temperature at each longitude around the globe. The thermal equator does not coincide with the geographical equator. The highest absolute temperatures are recorded in the Tropics but the highest mean annual temperatures are recorded at the equator. But because local temperatures are sensitive to the geography of a region, and mountain ranges and ocean currents ensure that smooth temperature gradients (such as might be found if the Earth were uniform in composition and devoid of surface irregularities) are impossible, the location of the thermal equator is not identical to that of the geographic Equator. Further, we know that the Earth reaches perihelion (the minimum distance from the Sun in its orbit) in early January and is at aphelion (maximum distance) in early July. During the winter season of the respective hemispheres, the angle of incidence of the sun’s rays is low in the tropics. The average annual temperature of the tropical regions is, therefore, lower than the observed near the equator, as the change in the angle of incidence is minimum at the equator. The thermal equator shifts towards the north and south with the north-south shift in the position of vertical rays of the sun. However, the annual average position of the Thermal equator is 5° N latitude. The reason is that the highest mean annual temperature shifts towards northwards during the summer solstice to a much greater extent than it does towards the south at the time of winter solstice. Prelims USP (Geography) by Vikas Ahlawat Sir & Team M