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Shun Lee Catholic Secondary School Advanced Level – Geography – Climatic System Chapter 1 Climatic System and Our Atmosphere 1.1 Components of the Climatic System There are four physical components within the climatic systems: Atmosphere the earth’s gaseous envelope Hydrosphere liquid water over the surface of the Earth Lithosphere land masses: mountain, ocean basins, the surface rocks, sediments and soil Biosphere all living organisms Figure 1.1 Interaction of Different Spheres (After John Wiley & Sons, 1996) Atmosphere Hydrosphere Biosphere Lithosphere Chapter 1 Climatic System- P1 Written by Clement Cheng Chapter 1 Climatic System and Our Atmosphere 1.2 Our Atmosphere 1.2.1 (Vertical) Layering of the Atmosphere Figure 1.2 The generalized vertical distribution of temperature and pressure up to about 110 km. Note particularly the tropopause and the zone of maximum ozone concentration with the warm layer above. Data based on Valley, 1965 Referring to Figure 1.2, how do the climatologists divide the atmosphere into different layers? The change in temperature. Chapter 1 Climatic System– P2 Written by Clement Cheng Shun Lee Catholic Secondary School Advanced Level – Geography – Climatic System With reference to Figure 1.2, fill in the following blanks. Vertical Position Change in temperature with height Importance / Special remarks The lower portion of the thermosphere is mainly of nitrogen and oxygen. Thermosphere (熱成層) 90 km or above increase Low atmospheric pressure; only 0.001% of its sea level value. This layer is affected by cosmic radiation, solar X-rays and ultraviolent radiation which cause ionization. Mesosphere(中間層) 55-80 km decrease The pressure of the mesosphere is very low ranging from 1mb at 50 km to 0.01 mb at 90km. Stratosphere (平流層) 20-50km increase The stratosphere is particularly effective in screening out harmful ultraviolent rays from the sun and is thus a vital shield for lifeforms at the surface. It contains 75% of the total molecular or gaseous mass of the atmosphere and virtually all the water vapour and aerosols. The weather ceiling or the inversion layer is called tropopause. 0-12 km Decrease at a mean The tropopause limits convection. Troposphere(對流層) (ranging rate about 6.5 The height of the tropopause is not constant spatially and temporally. The from 8 km – C/km height of the tropopasue at any point is correlated with the temperature, which 16km) are in turn related to the factors of latitude, season and daily change in the surface pressure. There are marked variations in the altitude of the tropopause with latitude, from about 16km at the equator where there is great heating and vertical convective turbulence to only 8 km at the poles. Chapter 1 Climatic System- P3 Written by Clement Cheng Shun Lee Catholic Secondary School Advanced Level – Geography – Climatic System 1.3 Spatial Distribution of Gases in the Atmosphere The earth’s atmosphere consists of a mixture of various gases surrounding the earth to a height of many kilometres. The air is densest at sea level and thins rapidly upward. Although almost the entire atmosphere (about 97%) lies within 30% of the earth’s surface, the upper limit of the atmosphere can be drawn approximately a height of 10, 000 km. 1.4 Internal Components of the Atmosphere (A) Gas Components Symbol Per cent by Volume (Dry air) Nitrogen N2 78.08 Oxygen O2 20.98 Argon Ar 0.93 Carbon dioxide CO2 0.035 Neon Ne 0.0018 Helium He 0.0005 Methane CH4 0.0017 Krypton Kr 0.0011 Hydrogen H 0.00005 Nitrous oxide N2O Trace Xenon Xe 0.00009 Carbon monoxide CO Trace Ozone O3 0.00006 Water vapour H2O Variable (0-4) Table 1.1 Average composition of the dry atmosphere below 25 km Chorley, 1992) 1. Nitrogen and oxygen Common Characteristics: Dominant gas Remarkably constant in the lowest 16 km Nitrogen is an importance source of fertilizer. Oxygen (a) is the most important gas for life. (b) is needed for combustion (c) reacts with solid rock causing chemical weathering or reacts with iron Chapter 1 Climatic System- P5 Written by Clement Cheng (Barry and Chapter 1 Climatic System and Our Atmosphere 2. Ozone Ozone is usually found in the upper stratosphere Produced by the high level breakup of oxygen molecules by solar ultraviolet radiation Destroyed by reactions involving nitrogen oxides and chlorine (CI) (the latter generated by CFCs, volcanic eruptions and vegetation burning) in the middle and upper stratosphere 3. Carbon dioxide It is released from the interior of the earth and produced by respiration, soil processes combustion and volcanic activity. Conversely, it is dissolved in the ocean and consumed by the process of plant photosynthesis. Carbon dioxide is of great importance in atmospheric processes because of its ability to absorb radiant heat. Therefore, carbon dioxide augments the warming of the lower atmosphere by radiant energy coming from the sun and from the earth’s surface. 4. Water Vapour Variable in proportion Dominant in the lower atmosphere Water vapour gets into the atmosphere through evaporation from oceans and land surfaces as well as evaportranspiration from plants In arid areas, there is little water to be evaporated so the atmosphere is also dry, containing only about 0.5% to 1.0% of water vapour. In humid areas, this figure may rise to 3% to 4%. (B) Solid 1. Dust Origin: (a) They have been swept into the air from dry desert plain, lake beds and beaches or explosive volcanoes. Strong winds blowing over the ocean lift droplets of spray into the air. These may dry out, leaving as residues tiny crystals of salt that are carried high into the air. (b) Forest and brush fires are another sources of atmospheric dust particles. (c) Some are due to the combustion of fuel in the industrial processes. Chapter 1 Climatic System– P6 Written by Clement Cheng Shun Lee Catholic Secondary School Advanced Level – Geography – Climatic System Effects of Occurrence of Dust: Dust contributes to the occurrence of twilight and the red colours of sunrise and sunset. Dust also serve as nuclei or centres around which water vapour condenses to produce cloud particles. 2. Volcanic dust 3. Salt It is whipped into the air by wave and wind action on sea water. The water evaporates leaving common salt, sodium chloride, behind. 4. Smoke It is far the most important content of the earth’s atmosphere. 1.5 Importance of the Atmosphere The atmosphere is important in the following ways: Allow plants and animals to survive Shields us from harmful radiation Stabilize the differences in temperature between tropical and polar regions Reduces losses of heat from the earth’s surface Provides water to sustain life Chapter 1 Climatic System- P7 Written by Clement Cheng