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Published byKerrie Cummings Modified over 9 years ago
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Mountain waves (Mountain-induced clouds)
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Hydraulic jump or rotor clouds in the Owens Valley Looking south on east side of Sierras; photo by glider pilot Robert Symons
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Lenticular clouds http://www.photolib.noaa.gov/historic/nws/wea00108.htm
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Lenticular clouds over Lake Tahoe (photo by RGF)
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Lenticular clouds http://www.photolib.noaa.gov/historic/nws/wea00010.htm
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Lenticular/cap/banner clouds over Mt. Rainier http://www.phototripusa.com/images/rwarfield/rw_3843_12.html
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Lee waves forced by the Appalachians 13 April 2007
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Lee waves downwind of Rockies 17 March 2005
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Lee waves in Nevada 17 March 2005
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Lee waves on Mars http://www.solarviews.com/raw/mars/leewave.gif
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Background on gravity waves and pendulum equations
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An oscillating parcel in a stable environment z’ = parcel vertical displacement N = Brunt-Vaisalla frequency Assumed solution: wavy in time… Result: where
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Environmental response to oscillating parcels Assumed solution wavy in time & space where
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Gravity wave frequency equation Two waves - opposite directions Period shorter in more stable environment Horizontal phase speeds Still proportional to N
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DTDM animation input_strfcn_isolated_nowind.txt
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Phase line tilt with height Westward wave tilts westward with height; Eastward wave tilts eastward Tilt implies vertical propagation
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Adding a mean flow (constant w/ height) Owing to mean flow, one wave speeds up, one slows down Mountain waves are horizontally stationary gravity waves
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Mountain wave analysis Adiabatic, Boussinesq, inviscid –But linearize about a mean state with wind, as well as vertical shear and even curvature shear, so –Assume locally steady state
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Mountain wave equation l 2 = Scorer parameter
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Cases to be examined Sinusoidal terrain –l 2 constant with height – flow with constant stability and mean wind –l 2 variable with height Isolated mountain Conditions for wave trapping leading to lenticular clouds
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l 2 < k 2 Narrow mountain Waves decay w/ z l 2 > k 2 Wide mountain Waves preserved w/ z, mimic mountain shape Sinusoidal mountain
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Isolated ridge Narrow mountain wide mountain l 2 < k 2 l 2 > k 2
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More stable layer below - trapped lee waves & lenticular/lee wave clouds
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