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Winds

Winds. Annual mean winds. Yin (2000) JAM. Annual Cycle in Wind. Annual cycle amplitude. Yin (2000) JAM. Peak Wind Season. Time of peak wind. Yin (2000) JAM. Diurnal Mountain Winds. Diurnal mountain winds develop from terrain of all scales

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Winds

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  1. Winds Annual mean winds Yin (2000) JAM

  2. Annual Cycle in Wind Annual cycle amplitude Yin (2000) JAM

  3. Peak Wind Season Time of peak wind Yin (2000) JAM

  4. Diurnal Mountain Winds • Diurnal mountain winds develop from terrain of all scales • Circulations arise as a result of differential heating between the ground in regions of complex terrain and free atmosphere at the same elevation • During day, higher terrain is an elevated heat source • During night, higher terrain is an elevated heat sink

  5. Sacramento Valley Zaremba and Carroll (1999) JAM

  6. Grand Canyon Whiteman et al. 1999 JAM

  7. Kali Gandaki Valley Egger et al. (2000) MWR

  8. Mountain wind systems • Slope winds- driven by horizontal temperature contrasts between air over valley sidewalls and air over center of valley • Along-valley winds- driven by contrasts along valley’s axis and nearby plain • Cross-valley winds- driven by contrasts between opposing sidewalls • Mountain-plain winds- driven by contrasts between plateau and nearby plains

  9. Whiteman (2000) Mountain Wind Systems

  10. Terminology • Katabatic wind: cold flow of air travelling downward or down a slope • Anabatic wind: air current or wind rising up a slope

  11. Whiteman (2000) Slope Winds

  12. Slope flows • Closed circulation driven by horizontal temperature contrasts between the air over the slope and the air at the same level over the center of the valley • Speeds- 1-5 m/s with maximum a few meters above the ground • Increase in speed as length of slope increases (Antarctica 14-30 m/s) • Strongest downslope at sunset; strongest upslope in midmorning • Depth of downslope ~5% of drop in elevation from top • Upslope flows increase in depth as move upslope • Stronger the stability, shallower the slope flows • Downslope flows converge into gullies; upslope flows converge over higher ground between gullies

  13. Whiteman (2000) g’ g Warm Cold Cold Warm Du’/dt = g’ (ren- r)/r=g’ (T-Ten)/Ten= g’ (Q-Qen)/Qen Slope flows

  14. Basin Circulations • Enclosed terrain features develop slope flows but weak along-valley circulations • Enhanced heating during the daytime and cooling at night as a result of absence of along-valley advection of cool/warm air • Light winds

  15. Whiteman (2000) Night flows

  16. Whiteman (2000) Thermal belt

  17. Slope Flows in Peter Sink Basin • Record cold temperature in Utah: Peter Sinks –57C • Clements (2001) conducted field program in remote basin in northern Utah to study slope flows • Field program held 8-12 Sept. 1999

  18. Peter Sinks

  19. North Peter Sink Vegetation inversion

  20. Peter Sinks Terrain

  21. Perimeter

  22. Instrumentation Layout

  23. Net Radiation and Sonic Anemometer

  24. Surface Energy Budget- Idealized Whiteman (2000)

  25. Surface Energy Budget- Peter Sinks Strong net heating during day; surface losing energy during night

  26. Surface Temperature Variation Coldest air in the basin- warm air on slopes

  27. Tethersonde Operations

  28. VerticalStructurein basin dw/dt = -g/Qen(dQen/dz)dz Stability increases as evening progresses Winds weaken with time

  29. Temperature Mast on Slope

  30. Temperature Variation on Slope Strong inversion below 2 m; isothermal above

  31. Vertical Structure on Slope Light drainage winds on slopes; nonexistent most of the time

  32. Potential Temperature Profiles Along Slope Observations from Peter Sinks do not agree with classical model of relatively deep cold air on slopes draining down into basin

  33. Morning Transition

  34. Morning Transition dw/dt = -g/Qen(dQen/dz)dz Stability decreases as morning progresses Winds strengthen with time

  35. Katabatic flow Poulos et al. 2000 MWR

  36. Simulation of Katabatic Wind Poulos et al. (2000) MWR

  37. Antarctica Katabatic Winds Bromwich (1989) BAMS

  38. Convergence Divergence Divergence Salt Lake Valley: Interaction of Slope and Valley Winds October 2000. M. Splitt

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