Microclimates

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Grade 12 Climatology. SA curriculum. Microclimates.

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Microclimates

  1. 1. Microclimates Microclimates Valley Climates Slope Aspect. Anabatic and Katabatic Winds. Land and Sea Breezes Influence of Local Climates on human activities. City Climates Reasons for differences between rural and urban climates. Urban heat Islands. Pollution Dome. Strategies to reduce the heat island effect
  2. 2. Microclimates VALLEY CLIMATES • Slope Aspect • Anabatic and Katabatic winds • Land and Sea Breezes • Influence of local climates on human activities
  3. 3. Slope Aspect
  4. 4. N Facing slopes (in the SH) are warmer w S N facing slopes in the SH are warmer since theN facing sun’s rays strike them directly. slope E Click here for video N
  5. 5. VALLEY CLIMATES: SLOPE ASPECT (SH) S O U T H WARMER NO SNOW SNOW COLDER N O R T H
  6. 6. Slope Winds: Anabatic winds
  7. 7. KATABATIC WIND
  8. 8. ANABATIC WIND
  9. 9. Mountain Winds – can you correctly order these statements? Move the text boxes around and insert the arrows. Similar circumstances can lead to frost and fog hollows in hilly regions. As the cold air accumulates in the valley, fog or frost may form. Under humid conditions, clouds may form over the valley sides On cold still nights, upper mountain surfaces rapidly lose heat. The air becomes chilled and more dense and flows down the valley sides as a katabatic wind. On a hot still days, air over a heated valley floor will expand and rise causing anabatic draughts to move up the valley side. Anabatic and Katabatic winds are also more pronounced under anticyclonic conditions in mountainous areas.
  10. 10. Mountain Winds Answer Anabatic and Katabatic winds are also more pronounced under anticyclonic conditions in mountainous areas. On a hot still days, air over a heated valley floor will expand and rise causing anabatic draughts to move up the valley side. Under humid conditions, clouds may form over the valley sides On cold still nights, upper mountain surfaces rapidly lose heat. The air becomes chilled and more dense and flows down the valley sides as a katabatic wind. Similar circumstances can lead to frost and fog hollows in hilly regions . As the cold air accumulates in the valley, fog or frost may form.
  11. 11. Katabatic Wind
  12. 12. Anabatic and Katabatic Winds Explain what causes the above wind to blow: Explain what causes the above wind to blow:
  13. 13. Anabatic Winds An anabatic wind is a wind which blows up a steep slope or mountain-side during the day, driven by sunshine heating the slope. A hill or mountain-top is warmed by the sun, which in turn heats the air just above it. This air becomes relatively warmer and lighter than other air at a similar altitude over an adjacent valley which does not get warmed as much because of the greater distance to the ground below it and / or if it is in shade. This warmer, lighter air will rise through convection, creating a lower-pressure region into which the higher-pressure air at the bottom of the slope gets drawn, causing the wind.
  14. 14. Katabatic Winds Opposite of Anabatic Wind, downslope movement as air cools. Can form fog or mist at bottom of slope in valley
  15. 15. Convection currents Local weather is affected by the movement of air masses all over the world. Some of this movement happens because the Sun heats the surface of the Earth unevenly. Temperature differences in the air cause convection currents. Convection currents in the atmosphere move warm air into colder areas. These wind currents take place anywhere there are temperature differences in the air. This often happens in places with nearby water.
  16. 16. Sea breezes and land breezes
  17. 17. Sea Breeze
  18. 18. Sea and Land breezes There are daily changes in wind direction due to unequal heating and cooling of land versus water. Warm air during day over land rises and cool air from sea moves onshore (with or without water vapor) causing a Sea Breeze. Sea Breeze LP HP Land Breeze LP HP
  19. 19. Daytime Onshore Breeze Night time Offshore Breeze
  20. 20. Video: Sea breezes
  21. 21. Local winds can act together to form strong winds Spot the error!
  22. 22. Microclimates URBAN CLIMATES • Reasons for differences between rural and urban climates. • Urban Heat Islands. • Pollution Dome. • Strategies to reduce the Heat Island effect.
  23. 23. VIDEO 1 ON URBAN HEAT ISLAND
  24. 24. VIDEO 2: THE HEAT ISLAND EFFECT
  25. 25. Why are cities warmer than rural areas? BUILDINGS
  26. 26. CHARACTERISTICS OF CITY CLIMATES
  27. 27. Microclimates: Cities
  28. 28. Complete the following. Go into editing mode: Factors that cause the Urban Heat Island effect: Artificial Material: Artificial Heat production: Urban Morphology: Spatial Growth: Dust and pollution particles: Dust and other particles serve as: More fog and pollution:
  29. 29. Factors causing cities to be warmer
  30. 30. Pollution Dome INSOLATION During day – land heated WARM AIR POLLUTED AIR TRAPPED Air close to surface- cooler Adiabatic warming occurs with descending stable air in Radiation faster if anticyclones. no clouds This compression can lead to a temperature inversion at 1 or 2 In night km above ground. surface This happens because on clear cools off nights the ground cools more quickly and rising air warms If there is sufficient water vapour, relative humidity can increase to 100% Clouds and fog can then form which often stays into the next Cold air morning. decends In cities this layer can trap pollutant particles and lead to health threatening fog (smog; smoke and fog)
  31. 31. EXAMINATION QUESTION 1 2 3 4 What is a heat island? Which part of the city is experiencing the highest temperature? How have peoples lives been changed by heat islands. Whet can be done to reduce high temperatures in cities?

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