inversion effects on lee-wave rotors simon vosper, stephen mobbs, ralph burton institute for...
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![Page 1: Inversion Effects on Lee-wave Rotors Simon Vosper, Stephen Mobbs, Ralph Burton Institute for Atmospheric Science University of Leeds, UK](https://reader036.vdocuments.us/reader036/viewer/2022062410/56649d4c5503460f94a2ae7b/html5/thumbnails/1.jpg)
Inversion Effects on Lee-wave Rotors
Simon Vosper, Stephen Mobbs, Ralph Burton
Institute for Atmospheric ScienceUniversity of Leeds, UK
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UK Met Office BLASIUS model Dry Boussinesq equations of motion using a first-order
(mixing-length) turbulence closure scheme Free-slip and no-slip (via a log-law formulation) lower-
boundary conditions 2 dimensional bell-shaped ridge Upstream wind independent of height, apart from within the
boundary layer in the no-slip case Upstream stratification neutral in a layer immediately above
the ground, capped by a sharp temperature inversion Above inversion buoyancy frequency independent of height
(N=0.01 s-1) Range of inversion strengths (measured by the difference
in potential temperature across the inversion Δθ) and inversion heights, z
i
Numerical Model
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![Page 4: Inversion Effects on Lee-wave Rotors Simon Vosper, Stephen Mobbs, Ralph Burton Institute for Atmospheric Science University of Leeds, UK](https://reader036.vdocuments.us/reader036/viewer/2022062410/56649d4c5503460f94a2ae7b/html5/thumbnails/4.jpg)
No slip case. Horizontal flow speed shaded, potential temperature contoured at 1K intervals. F
i=0.6, z
i=800 m, H=400 m
Closed Rotors
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No slip case. Horizontal flow speed shaded, potential temperature contoured at 1K intervals. F
i=0.4, z
i=800 m, H=400 m
Stationary Hydraulic Jump
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No Slip Case Closed rotors Stationary hydraulic jumps
Free Slip Case No closed rotors Stationary hydraulic jumps
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Regime Diagram – No slip Case
Solid line – critical Fi trapped lee waves (linear theory)
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10 min wind vectors, 9 February 2001, East Falkland
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High degree of spatial variability during rotor streaming Suggests the use of wind variances in rotor diagnostics Calculate instantaneous spatial standard deviation of
wind at stations downwind of orography σ given by
Rotor diagnostics σ and σU Energy argument suggests that closed rotors can occur if
Analysis of Observations of Rotor Streaming
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Time series of rotor diagnostics
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Regime Diagram – Observations
Solid line - R=1
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Mean Speed-up and Rotors
Uup
is wind speed upstream of mountains U is mean wind speed over 8 stations downwind of
mountains
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Regime Diagram – Observations
Idealised modelling demonstrates connection between rotor streaming and trapped lee waves on inversion
Needs no-slip boundary condition
Correlation between inversions observed downwind of mountains and rotors is low
Rotor activity (spatial variability of wind) directly proportional to mean speed-up