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Class #4: Stability, cloud development, and precipitation

Class #4: Stability, cloud development, and precipitation. Chapters 6 and 7. Stability & Cloud development. Chapter 6. Fig. 6-CO, p. 140. Fig. 6-1, p. 142. Importance of Clouds. Release heat to atmosphere Help regulate energy balance Indicate physical processes. Atmospheric Stability.

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Class #4: Stability, cloud development, and precipitation

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  1. Class #4: Stability, cloud development, and precipitation Chapters 6 and 7 Class #4 Monday, July 12, 2010

  2. Stability & Cloud development Chapter 6 Class #4 Monday, July 12, 2010

  3. Fig. 6-CO, p. 140

  4. Fig. 6-1, p. 142

  5. Importance of Clouds • Release heat to atmosphere • Help regulate energy balance • Indicate physical processes Class #4 Monday, July 12, 2010

  6. Atmospheric Stability • Clouds from as air rises and cools • Adiabatic processes: change in temperature without giving or removing • Dry rate = 10°C/1000m • Moist rate = 6°C/1000m • Stability is a state of equilibrium in terms atmospheric movement; no vertical movement occurs Class #4 Monday, July 12, 2010

  7. Determining Stability • Warm air rises or is unstable • Cool air sinks or is stable • Compare air parcel lapse rate to environmental lapse rate Class #4 Monday, July 12, 2010

  8. Class #4 Monday, July 12, 2010

  9. Table 6-1, p. 143

  10. Determining Stability • Stable environment • Environmental lapse rate less than moist lapse rate • If an air parcel is forced it will spread horizontally and form stratus clouds • Usually a cool surface (radiation, advection) • Inversion: warm over cool. Class #4 Monday, July 12, 2010

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  14. Fig. 6-6, p. 145

  15. Determining Stability • Special Topic: Subsidence Inversions • Strong subsidence exacerbates air pollution due to the lack of vertical motion. • Pollution is not diluted. Class #4 Monday, July 12, 2010

  16. Determining Stability • An Unstable Atmosphere • Environmental lapse rate greater than the dry adiabatic lapse rate • As air parcel rises it forms a vertical cloud • Convection, thunderstorms, severe weather Class #4 Monday, July 12, 2010

  17. Class #4 Monday, July 12, 2010

  18. Determining Stability • A Conditionally Unstable Atmosphere • Moist adiabatic lapse rate is less than the environmental lapse rate which is less than the dry adiabatic lapse rate • Stable below cloud unstable above cloud base • Atmosphere usually in this state Class #4 Monday, July 12, 2010

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  24. Fig. 6-13, p. 149

  25. Fig. 6-14, p. 149

  26. Fig. 1, p. 150

  27. Determining Stability • Causes of Instability • Cool air aloft (advection, radiation cooling in clouds) • Warming of surface (insolation, advection, warm surface) Class #4 Monday, July 12, 2010

  28. Cloud Development • Clouds develop as an air parcel rises and cools below the dew point. • Usually a trigger or process is need to initiate the rise of an air parcel. Class #4 Monday, July 12, 2010

  29. Class #4 Monday, July 12, 2010

  30. Cloud Development • Convection • Differential land surface heating creates areas of high surface temperature. • Air above warm land surface heats, forming a ‘bubble’ of warm air that rises or convection. • Cloud base forms at level of free convection. Class #4 Monday, July 12, 2010

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  32. Stepped Art Class #4 Monday, July 12, 2010 Fig. 6-16, p. 152

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  36. Fig. 2, p. 155

  37. Cloud Development • Topography • Orographic uplift • Orographic clouds • Windward, leeward, rain shadow • Lenticular clouds Class #4 Monday, July 12, 2010

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  42. Cloud Development • Topic: Adiabatic charts • Adiabatic charts show how various atmospheric variables change with height: pressure, temperature, humidity. Class #4 Monday, July 12, 2010

  43. Fig. 3, p. 158

  44. Fig. 4, p. 158

  45. Fig. 5, p. 158

  46. Fig. 6, p. 159

  47. Fig. 7, p. 159

  48. Cloud Development • Changing cloud forms • Stratus clouds can change to cumulus clouds if the top of the cloud cools and the bottom of the cloud warms. • Alto cumulus castellanus: towers on alto stratus • If moist stable air without clouds is mixed or stirred it can form stratocumulus clouds. Class #4 Monday, July 12, 2010

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  50. Class #4 Monday, July 12, 2010

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