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Published byEthel Miller Modified over 9 years ago
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Time-Dependent Mountain Waves and Their Interactions with Large Scales Chen, C.-C., D. Durran and G. Hakim Department of Atmospheric Sciences University of Washington
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The Goal Follow mountain-wave evolution in a realistic, but simple time-varying large- scale flow. Avoid artificial initialization Capture the decaying phase of the waves Examine feedback of the waves on the large-scale flow.
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The Simulations Numerical model Boussinesq (“compressible,” nonhydrostatic) f-plane Terrain-following coordinates Gravity-wave absorbing upper boundary Parameterized subgrid-scale mixing Multiply nested grids
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The Nested Grids x 1 = y 1 = 27 km x 2 = y 2 = 9 km x 3 = y 3 = 3 km z = 150~500 m half width a = 12.5 km aspect ratio = 3
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Initial Condition Ingredients Square wave in streamfunction plus a mean flow Doubly periodic x = y =2700 km
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Initial Streamfunction Mean wind 7.5 m/s 0 < local u < 15 m/s Period = 100 hrs (~4 days) Constant N (2/3 < Nh/u < )
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w & velocity vector @ 5km (x-y plane)
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w & theta & turbulent mixing coefficient (x-z cross-section)
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relative vorticity & velocity vector at surface
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PV @ 295K ~ 2.5km at t = 55 hrs
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PV @ 295K
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PV @ 295K, t = 0
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PV @ 295K, t =100hrs
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Summary—Near Mountain Flow Near mountain evolution Flow-around to flow-over to flow-around Low-level blocking Lee vortex generation and shedding Wave breaking Quasi-linear waves Acceleration phase not mirror image of deceleration phase (period is 4 days)
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Summary—Scale Interaction Localized dissipation creates PV dipoles in the lee of the barrier Adiabatic interactions with the larger scale PV creates significant synoptic-scale anomalies More analysis is on the way!
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