Winds

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Winds
Annual mean winds
Yin (2000) JAM
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Annual Cycle in Wind
Annual cycle amplitude
Yin (2000) JAM
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Peak Wind Season
Time of peak wind
Yin (2000) JAM
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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

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Sacramento Valley
Zaremba and Carroll (1999) JAM
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Grand Canyon
Whiteman et al. 1999 JAM
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Kali Gandaki Valley
Egger et al. (2000) MWR
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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
  valleys axis and nearby plain
• Cross-valley winds- driven by contrasts between
  opposing sidewalls
• Mountain-plain winds- driven by contrasts between
  plateau and nearby plains

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Mountain Wind Systems
Whiteman (2000)
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Terminology

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

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Slope Winds
Whiteman (2000)
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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

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Slope flows
Whiteman (2000)
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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

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Night flows
Whiteman (2000)
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Thermal belt
Whiteman (2000)
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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

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Peter Sinks
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North Peter Sink
Vegetation inversion
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Peter Sinks Terrain
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Perimeter
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Instrumentation Layout
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Net Radiation and Sonic Anemometer
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Surface Energy Budget- Idealized
Whiteman (2000)
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Surface Energy Budget- Peter Sinks
Strong net heating during day surface losing
energy during night
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Surface Temperature Variation
Coldest air in the basin- warm air on slopes
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Tethersonde Operations
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VerticalStructurein basin
dw/dt -g/Qen(dQen/dz)dz
Stability increases as evening progresses Winds
weaken with time
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Temperature Mast on Slope
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Temperature Variation on Slope
Strong inversion below 2 m isothermal above
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Vertical Structure on Slope
Light drainage winds on slopes nonexistent most
of the time
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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
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Morning Transition
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Morning Transition
dw/dt -g/Qen(dQen/dz)dz
Stability decreases as morning progresses Winds
strengthen with time
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Katabatic flow
Poulos et al. 2000
MWR
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Simulation of Katabatic Wind
Poulos et al. (2000)
MWR
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Antarctica Katabatic Winds
Bromwich (1989) BAMS
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Divergence Salt Lake Valley Interaction of Slope
and Valley Winds
October 2000. M. Splitt