Winds Yin (2000) JAM Annual mean winds
Annual Cycle in Wind Yin (2000) JAM Annual cycle amplitude
Peak Wind Season Yin (2000) JAM Time of peak wind
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
Sacramento Valley Zaremba and Carroll (1999) JAM
Grand Canyon Whiteman et al JAM
Kali Gandaki Valley Egger et al. (2000) MWR
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
Mountain Wind Systems Whiteman (2000)
Terminology Katabatic wind: cold flow of air travelling downward or down a slope Anabatic wind: air current or wind rising up a slope
Slope Winds Whiteman (2000)
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 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
Slope flows Whiteman (2000) Cold Warm Cold Du’/dt = g’ ( en - )/ =g’ (T-T en )/T en = g’ ( - en )/ en g g’
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
Night flows Whiteman (2000)
Thermal belt Whiteman (2000)
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
Peter Sinks
North Peter Sink Vegetation inversion
Peter Sinks Terrain
Perimeter
Instrumentation Layout
Net Radiation and Sonic Anemometer
Surface Energy Budget- Idealized Whiteman (2000)
Surface Energy Budget- Peter Sinks Strong net heating during day; surface losing energy during night
Surface Temperature Variation Coldest air in the basin- warm air on slopes
Tethersonde Operations
Vertical Structure in basin dw/dt = -g/ en (d en /dz)dz Stability increases as evening progresses Winds weaken with time
Temperature Mast on Slope
Temperature Variation on Slope Strong inversion below 2 m; isothermal above
Vertical Structure on Slope Light drainage winds on slopes; nonexistent most of the time
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
Morning Transition
dw/dt = -g/ en ( en / z)dz Stability decreases as morning progresses Winds strengthen with time
Katabatic flow Poulos et al MWR
Simulation of Katabatic Wind Poulos et al. (2000) MWR
Antarctica Katabatic Winds Bromwich (1989) BAMS
Divergence Salt Lake Valley: Interaction of Slope and Valley Winds Convergence Divergence October M. Splitt