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Chapter 27 - Clouds

Chapter 27 - Clouds. Use of Power Point design and animations with permission from Dr. Joby Hilliker ( West Chester University, West Chester, PA. CHAPTER 6 - CLOUDS. How is a cloud formed?

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Chapter 27 - Clouds

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  1. Chapter 27 - Clouds Use of Power Point design and animations with permission from Dr. Joby Hilliker ( West Chester University, West Chester, PA

  2. CHAPTER 6 - CLOUDS • How is a cloud formed? • An air parcel containing water vapor (gas) is cooled to the dewpoint such that the water vapor condensesto form water droplets (liquid). = Liquid water droplets • When condensation occurs, the air parcel is ”saturated”(RH=100%)

  3. Unsaturated Parcels Generic Cloud Saturated Parcels

  4. CHAPTER 6 - CLOUDS • When condensation occurs, the air parcel is ”saturated”(RH=100%) • The temp. at which saturation (and condensation) will occur is the dewpoint • The farther the dewpoint is below the air temp, the lower the RH, and the less likely clouds will form.

  5. 6 6 6 6 Density of Surrounding Air 6 z CHAPTER 6 - RISING PARCELS • How can an air parcel cool to the dewpoint? • Get it to rise! • How can this happen? • Density of parcel needs to be less than surrounding air 3 Density of Main Air Parcel

  6. 60 60 60 60 Temp. of Surrounding Air 60 z CHAPTER 6 - RISING PARCELS • Translate density into temperature: • Warmer air is less dense; Colder air is more dense • A parcel will rise if it’s warmer than surrounding air. • “Warm air rises” concept 70 Temp. of Main Air Parcel

  7. CHAPTER 6 - RISING PARCELS What happens when a parcel rises? • It expands • Finds itself in an environment with lesser density/pressure • It coolsadiabatically • Takes work (thermal energy) to expand parcel • adiabatic= no heat exchange between parcel and environment • parcels cools at the dry adiabatic lapse rate (DALR), which is 5.5°F / 1000 feet 60 F z 70 F

  8. CHAPTER 6 - RISING PARCELS To determine if a parcel will rise, compare: a. the parcel’s temperature which cools at a constant rate …at a given altitude to… b. temp. of surrounding parcels changes on a daily basis; is measured (i.e., the atmosphere) RULE #1: • As long as the rising parcel is warmerthan surrounding air parcels at a given altitude, the parcel will continue to rise • If parcel becomes colder, it will sink

  9. Parcels going all the way up to 50,000 feet!

  10. CHAPTER 6 - CASE #1 • Steep lapse rate (_________ ATMOSPHERE): Parcel rises to tropopause Result: Thunderstorms! UNSTABLE Parcel cools ...and if drops to dewpoint Lapse Rate (steep) Saturation z COLD Temperature HOT

  11. Cumulo-nimbus (Thunderstorm)

  12. Cumulonimbus

  13. Cumulonimbus

  14. CHAPTER 6 - CASE #2 • Steep lapse rate near ground, weak aloft: Parcel rises to a point, then stops Result: Cumulus (weak) Parcel cools Lapse Rate ...and if drops to dewpoint (steep) Saturation z COLD Temperature HOT

  15. "Cumulus" 3000 - 8000 feet

  16. Cumulus 3000 - 8000 feet

  17. Alto-cumulus 10000 - 20000 feet

  18. Alto-cumulus 10000 - 20000 feet

  19. Cirro-cumulus 20000-40000 feet

  20. CHAPTER 6 - CASE #3 • Weak lapse rate (_________ ATMOSPHERE): Parcel rises only slightly Result: Stratus STABLE Lapse Rate (weak) z COLD Temperature HOT

  21. "Stratus" 0 - 8000 feet

  22. Stratus 0 - 8000 feet

  23. Altostratus 10000 - 20000 feet

  24. Altostratus 10000 - 20000 feet

  25. Cirrostratus 20000 - 40000 feet

  26. CHAPTER 6 - SUMMARY OF CLOUDS • Cloud type reveals: …how quickly temperature is decreasing w/ height • CUMULUSSTRATUS Unstable AtmosphereStable Atmosphere High Lapse Rate Low Lapse Rate Deep, Vertical DevelopmentThin, Spread out

  27. CHAPTER 6 - SUMMARY OF CLOUDS • If parcel can rise: • Cloud Top = where parcel is no longer warmer than surrounding air • Cloud Base = where saturation occurs • What could I infer about atmosphere if it is CLEAR? • Sinking air • Lack of moisture (low dewpoint)

  28. Cirrus 30000 feet + Composed of Ice Crystals

  29. Contrails 30000 feet + Composed of Ice Crystals

  30. CLOUD NOMENCLATURE

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