1 / 36

Clouds: cool to dew point

Clouds: cool to dew point. 2 processes to change temperature Diabatic : energy added/removed Adiabatic : no energy exchange. Diabatic Processes. Add heat to water. Air loses energy. Warm air. Cool water. Diabatic Processes. Add heat to water. Air gains energy. Cool air. Warm water.

kiri
Download Presentation

Clouds: cool to dew point

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Clouds: cool to dew point • 2 processes to change temperature • Diabatic: energy added/removed • Adiabatic: no energy exchange

  2. Diabatic Processes Add heat to water Air loses energy Warm air Cool water

  3. Diabatic Processes Add heat to water Air gains energy Cool air Warm water

  4. Heat moves from warm to cold • Fog (not clouds) Diabatic Processes

  5. Cloud development Adiabatic Processes Work performed by expanding gas Change in internal energy

  6. Cloud development Adiabatic Processes Work performed by expanding gas Change in internal energy • Gas expands -> temperatures decrease • Gas contracts-> temperatures increase

  7. Adiabatic Processes • Dry air rises -> expands/cools • Dry Adiabatic Lapse Rate (DALR): 1oC/100m

  8. Adiabatic Processes • Lifting condensation level (LCL): Level at which the air becomes saturated

  9. Saturated air rises -> condensation • Latent heat release Cools at SALR Saturated air Cools at DALR Unsaturated air

  10. Saturated air rises -> condensation • Latent heat release • Saturated Adiabatic Lapse Rate (SALR): 0.5oC/100m • SALR < DALR Cools at SALR Saturated air Cools at DALR Unsaturated air

  11. Formation/Dissipation of Clouds • Adiabatic cooling of rising air Cools at DALR Unsaturated air

  12. Formation/Dissipation of Clouds • At LCL-> droplets form • Rise -> drops grow larger • Lifting stops, cloud development stops LCL Cools at SALR Saturated air

  13. Formation/Dissipation of Clouds Saturated air • Sinks: warming less due to evaporation • Reversible processes: reach original temperature Warms at SALR Unsaturated air Warms at DALR

  14. Environmental Lapse Rate (ELR) • Change in temperature with height • time, location, altitude

  15. Forms of Condensation • Dew: condensation on a surface • Air cools to dew point

  16. Forms of Condensation • Dew: condensation on a surface • Air cools to dew point • Early morning • Ground loses LW, cool diabatically • Clear, windless nights, no clouds

  17. Forms of Condensation • Frost: air cools to frost point; deposition • Separate ice crystals

  18. Forms of Condensation • Frozen dew: dew forms then freezes • Tight bond between ice and the surface. • “black ice”

  19. Forms of Condensation • Fog: cloud near the surface • Shallow or deep

  20. Forms of Condensation • Fog: cloud near the surface • Shallow or deep • Cool air to dew point, add moisture, mix cold & warm, moist air.

  21. Precipitation and Steam Fogs • Precipitation fog: evaporation of rain raise dew points • Steam fog: mix cold & warm, moist air • diabatic

  22. Radiation (ground) Fogs • Loose LW; cool air to dew point • Cloudless nights, light winds

  23. Radiation (ground) Fogs • “Burns off” at sunrise from surface upward • Scatters back SW (days?)

  24. Radiation (ground) Fogs • Mountain ranges on both sides • Farmland -> moisture • Zero visibility

  25. Valley Fogs • Cold dense air settles into low elevations • diabatic cooling

  26. Can be fatal: 5 Feb 2002 • 90 car pileup

  27. Advection Fogs • Warm, moist air moves over cooler surface • Diabatic cooling • San Francisco Bay in summer

  28. Advection Fogs • Warm, moist air moves over cooler surface • Diabatic cooling • Advected by stronger winds • San Francisco Bay in summer 1500 ft thick!

  29. Upslope Fogs • Adiabatic cooling • Moist air moves up slope • Expands and cools

  30. 1/3 of year Cape disappointment summer late summer and fall minimum

  31. Heat Index • We cool by sweating • High humidity slows evaporation

  32. Atmospheric Moisture and Climate Change • As temperatures and SST rise -> evaporation increases • Water vapor = greenhouse gas: Positive feedback cycle.

  33. Atmospheric Moisture and Climate Change • As temperatures and SST rise -> evaporation increases • Water vapor = greenhouse gas: Positive feedback cycle. • IPCC: Increase in surface specific humidity in cities with increasing temperatures (1976) • 4% rise in upper tropospheric water vapor. • RH = constant. Why?

  34. Atmospheric Moisture and Climate Change • Oceans: constant RH. • Land areas: decrease RH • Negative feedback: T rises, more LW emitted

  35. Atmospheric Moisture and Climate Change • Oceans: constant RH. • Land areas: decrease RH • Negative feedback: T rises, more LW emitted • Other feedbacks: • Increase moisture = increase in clouds • May reduce incoming SW • Increase LW absorbed

More Related