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HIGHER GEOGRAPHY PHYSICAL ENVIRONMENTS

HIGHER GEOGRAPHY PHYSICAL ENVIRONMENTS. ATMOSPHERE. Learning Intentions. Atmosphere. We will be learning about: The characteristics of the atmosphere and how they vary spatially and provide climate and weather conditions which interlink with other systems. Further development

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HIGHER GEOGRAPHY PHYSICAL ENVIRONMENTS

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  1. HIGHER GEOGRAPHY PHYSICAL ENVIRONMENTS ATMOSPHERE

  2. Learning Intentions Atmosphere We will be learning about: The characteristics of the atmosphere and how they vary spatially and provide climate and weather conditions which interlink with other systems. Further development Candidates should have a knowledge and understanding of:

  3. 1Global scale: ♦ effects of the atmosphere on the receipt of radiation at the Earth’s surface -causes of latitudinal variations of radiation receipt ♦ patterns of atmospheric and oceanic circulation and their influence on the redistribution of energy over the globe - principal circulation cells, pressure and wind belts, influence of ocean currents ♦ global climate change - physical and human causes of global warming 2 Regional scale - equatorial and savanna regions of Africa: ♦ nature, origin and movement of air masses, including convergence and divergence ♦ weather types associated with different air masses role of continental tropical and maritime tropical air masses on West African climate - particularly rainfall amounts and distribution.

  4. THE ATMOSPHERE

  5. Troposphere = main zone of weather and climate. lapse rate = decrease in temperature with altitude = 6.4ºC for every 1000metres = approximately 1ºC for every 150 metres

  6. Mt Everest (8800metres) Calculate the difference in temperature between sea level and the summit of the mountain.

  7. ATMOSPHERIC GASES Nitrogen - 78% Oxygen - 21% Carbon dioxide - 0.036% …...and rising!! Water vapour - variable - up to 4% over tropical oceans. (as humidity increases the relative amounts of other gases decrease).

  8. Global extremes of Temperature 58ºC San Luis Potosi, Mexico Al Aziziyah, Libya -88ºC Vostok Antarctica In the absence of an atmosphere the Earth would average about 30ºC less than it does at present. Life (as we now know it) could not exist.

  9. SOLAR INSOLATION reflectedby clouds and dust, water vapour and other gases in the atmosphere 100% 25% absorbedby clouds and dust, water vapour and other gases in the atmosphere 23% 52% reflectedby surface 6% absorbed by surface 46%

  10. SOLAR INSOLATION 100% solar insolation TOTAL ALBEDO = 25 + 6 = 31% 25% reflectedby atmosphere 23% absorbedby atmosphere TOTAL ABSORPTION = 23 + 46 = 69% 52% reaches surface 6% reflectedby surface 46% absorbed by surface

  11. ENERGY SURPLUS and DEFICIT The Earth's atmosphere is put into motion because of the differential heating of the Earth’s surface by solar insolation. The Poles receive less heat than the Tropics because: 1. Insolation has to pass through more of the Earth’s atmosphere 2. the angle of incidence of insolation and 3. higher levels of surface albedo.

  12. 3 2 1 Insolation has to pass through more of the Earth’s atmosphere 1 The angle of incidence of insolation - energy is spread out over a larger area because the sun’s rays strike the surface at a lower angle. 2 3 Higher levels of surface albedo - the ice-cap reflects more solar insolation

  13. Energy concentrated on a smaller surface area Angle of Incidence

  14. Describe the energy surplus and deficit across the globe

  15. There is a surplus of energy between 35N & 35S and incoming insolation exceeds outgoing radiation. Where outgoing radiation exceeds incoming insolation there is a deficit. Insolation rises sharply from 50 joules at the poles to 275 joules at the equator. Terrestrial radiation varies less, from 120 joules at the poles to 200 joules at the equator.Energy is transferred by atmospheric circulation and ocean currents.

  16. In theory an imbalance in energy receipt could result in lower latitudes becoming warmer and higher latitudes becoming even colder. In reality energy is transferred from lower latitudes (areas of surplus) to higher latitudes (areas of deficit) BY 1. ATMOSPHERIC CIRCULATION and 2. OCEAN CURRENTS

  17. 90º Pole 0º Equator DEFICIT 1. ATMOSPHERIC CIRCULATION 2. OCEAN CURRENTS SURPLUS

  18. deficit surplus 0º Equator 90º Pole NO! not directly

  19. 0º Equator 90º Pole TRANSFER of ENERGY by ATMOSPHERIC CIRCULATION

  20. TRANSFER of ENERGY by OCEAN CURRENTS 90º Pole 0º Equator

  21. ATMOSPHERIC CIRCULATION

  22. 0º Equator 90º Pole LP HP SINGLE CELL MODEL • At the Equator the atmosphere is heated • Air becomes less dense and rises. • Rising air creates low pressure at the equator. • Air cools as it rises because of the lapse rate. • Air spreads. • As air mass cools it increases in density and descends. • Descending air creates high pressure at the Poles. • Surface winds blow from HP to LP.

  23.  warm air is less dense therefore lighter  air rises in the Tropics  this creates a zone of LOW PRESSURE  air spreads N and S of the Equator  air cools and sinks over the Poles  this is a zone of HIGH PRESSURE  air returns as surface WINDS to the Tropics

  24. SINGLE CELL MODEL The single cell model of atmospheric circulation was developed to explain the transfer of energy from the Tropics to the Poles. This was later improved and a three cell model was developed. Today the three cell model is also considered to be an oversimplification of reality.

  25. HADLEY CELL ITCZ ITCZ = Inter-tropical convergence Zone (Low Pressure) STH = Sub-tropical High (High Pressure)

  26. 0º Equator 30º 60º 90º Pole LP HP LP HP THREE CELL MODEL Polar Cell Hadley Cell Ferrel Cell

  27. ENERGY TRANSFER Warm air rises at the Equator - Inter-Tropical Convergence Zone (ITCZ). Equatorial air flows to ~30º N then sinks to the surface and returns as a surface flow to the tropics. This is the Hadley cell. Cold air sinks at the North Pole. It flows S at the surface and is warmed by contact with land/ocean, by ~60º N it rises into the atmosphere. This the Polar cell. Between 60º N and 30º N there is another circulation cell. This is the Ferrel cell. The Hadley cell and the Polar cell are thermally direct cells. The Ferrel cell is a thermally indirect cell.

  28. Polar Cell Hadley Cell Ferrel Cell ENERGY TRANSFER Heat energy is transferred from the Hadley Cell to the Ferrel Cell and from the Ferrel Cell to the Polar Cell. In this way heat is transferred from the Equator where there is an energy surplus to the Poles where there is an energy deficit.

  29. 0º Equator 30º 60º 90º Pole WINDS divergence divergence convergence convergence LP HP LP HP winds blow from high pressure zones to low pressure zones

  30. 0º Equator 30º 60º 90º Pole WINDS diverence divergence convergence convergence LP HP LP HP Explain how circulation cells in the atmosphere assist in the Transfer of energy from areas of surplus to areas of deficit

  31. Warm air rises at the Equator 0˚ (LP)and travels into the upper atmosphere to around 30˚ N and S, cools and sinks (HP) – this means it is thermally direct. Air moves from the tropical high to the low pressure area at the equator creating the Hadley Cell Air rises at 60˚N and S (LP) into the upper atmosphere where it flows to the Poles and sinks at 90˚N and S (HP). The Polar cell is also thermally direct as warm air rises, cools and sinks. The Ferrel cell is placed between the Hadley cell and Polar cell. Unlike the other two types of cells, the Ferrel cells are known as thermally indirect cells because their motion is dependent upon the motion within the Hadley and Polar cells in between which they are found. In this way energy is transferred from the equator (area of surplus) to the poles (area of deficit)

  32. CONVERGENCE and …………DIVERGENCE

  33. PLANETARY WIND SYSTEM

  34. Coriolis occurs because the Earth rotates. Earth rotates about its axis every 24 hours. Distance around the equator is ~25,000 miles the earth is travelling east at ~ 1,000 miles per hour. Distance around the Earth at 40ºN ~19,000 miles the earth is travelling east at ~800mph. The Coriolis effect results from this difference in velocity. In the Northern hemisphere the Coriolis effect deflects movement to the right. In the Southern hemisphere the Coriolis effect deflects movement to the left. The combination of atmospheric cells and Coriolis effect lead to the wind belts. Wind belts drive surface ocean circulation CORIOLIS

  35. PLANETARY WINDS High Pressure Coriolis effect WIND pressure gradient force Low Pressure Winds are named by the direction they blow from.

  36. Be very, very careful what you put into that head, because you will never, ever get it out. Thomas Cardinal Wolsey (1471-1530) CORIOLIS The water in a sink rotates one way as it drains in the northern hemisphere and the other way in the southern hemisphere. Called the Coriolis Effect, it is caused by the rotation of the Earth. This is NOT true! The Coriolis force is so small, that it plays no role in determining the direction of rotation of a draining sink anymore than it does the direction of a spinning CD.

  37. 90ºN Temperate Low LP 60ºN 30ºN Sub-tropical High - Horse Latitudes HP Equatorial Low - Doldrums LP 0º Sub-tropical High - Horse Latitudes HP 30ºS Temperate Low LP 60ºS 90ºS WIND BELTS Polar easterlies South westerlies NE Trades SE Trades North westerlies Polar easterlies

  38. convergence LP 60ºN 30ºN divergence Sub-tropical High HP convergence Inter-tropical convergence zone LP 0º 30ºS divergence Sub-tropical High HP convergence LP 60ºS 90ºS WIND BELTS Polar easterlies South westerlies NE Trades SE Trades North westerlies Polar easterlies

  39. WIND BELTS

  40. WIND BELTS Northern Hemisphere Polar Easterlies Blowing from the Polar High Pressure zone to about 60ºN Westerlies Blowing from Sub-Tropical High Pressure zone to about 60ºN Northeast Trade Winds Blowing from Sub-Tropical High Pressure zone to Equatorial Low Pressure zone. Southern Hemisphere Southeast Trade Winds Blowing from Sub-Tropical High Pressure zone to Equatorial Low Pressure zone. Westerlies Blowing from Sub-Tropical High Pressure zone to about 60ºS Polar Easterlies Blowing from the Polar High Pressure zone to about 60ºS

  41. Series of High and Low pressure centres approx. every latitude pressure zones associated with descending air () Low pressure zones associated with air (convergence) circulation cells in each hemisphere: thermally direct thermally indirect Polar Cell thermally direct Wind is the horizontal movement of air arising from differences in . Very little wind at the Equator () because air is being convected . Little wind at 30ºN and S (Horse Latitudes) because direction of air movement is down. Winds always blow from an area of Pressure to Pressure. Winds are affected by the Effect. This is a consequence of motion on a rotating sphere. Acts to the of direction of motion in Northern Hemisphere Acts to the of direction of motion in the Southern Hemisphere Major wind belts of the Earth surface 0 to 30ºN Southeast Trades 30 to 60ºN/S 60 to 90ºN/S Polar SLIDE 37

  42. Series of High and Low pressure centres approx. every 30º latitude High pressure zones associated with descending air (divergence) Low pressure zones associated with rising air (convergence) Three circulation cells in each hemisphere: Hadley Cell thermally direct Ferrel Cell thermally indirect Polar Cell thermally direct Wind is the horizontal movement of air arising from differences in pressure. Very little wind at the Equator (Doldrums) because air is being convected upward. Little wind at 30ºN and S (Horse Latitudes) because direction of air movement is down. Winds always blow from an area of High Pressure to Low Pressure. Winds are affected by the Coriolis Effect. This is a consequence of motion on a rotating sphere. Acts to the Right of direction of motion in Northern Hemisphere Acts to the Left of direction of motion in the Southern Hemisphere Major wind belts of the Earth surface 0 to 30ºN Northeast Trades 0 to 30ºS Southeast Trades 30 to 60ºN/S Westerlies 60 to 90ºN/S Polar easterlies

  43. INTER-TROPICAL CONVERGENCE ZONE (ITCZ)

  44. 23º The most intense heating of the sun, occurring at the so-called thermal equator, annually moves between the tropics. On or around June 20th each year the sun is overhead at 23½ºN, the Tropic of Cancer. On or around December 20th the the sun is at overhead at 23½ºS, the Tropic of Capricorn. These two dates are the solstices. Twice a year, at the equinoxes, on or around March 20th and September 20th the overhead sun crosses the equator. This annual north to south and back again "shift" of the thermal equator shifts the belts of planetary winds and pressure systems to the north and to the south as the year turns.

  45. June Summer Solstice 23½ºN TROPIC of CANCER September Autumn Equinox March Spring Equinox 0º EQUATOR December Winter Solstice 23½ºS TROPIC of CAPRICORN

  46. ITCZ

  47. ITCZ JULY ITCZ JANUARY

  48. The location of the ITCZ varies throughout the year The ITCZ over land moves farther north or south than the ITCZ over the oceans due to the variation in land temperatures. ITCZ JANUARY ITCZ JULY

  49. http://www.cla.sc.edu/geog/faculty/carbone/modules/newmods/africa-itcz/http://www.cla.sc.edu/geog/faculty/carbone/modules/newmods/africa-itcz/ The blue shading on the map shows the areas of highest cloud reflectivity, which correspond to the average monthly position of the ITCZ.

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