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Laboratory and Field Measurements of Environmental Stratified Flows

Stellar Hydro Days, 26-28 July, 2006 Los Alamos. Laboratory and Field Measurements of Environmental Stratified Flows. Marko Princevac July 28, 2006. Outline. Slope Flows Entrainment in Katabatic Current Eddy Diffusivity Waves vs. Turbulence Morning Inversion Break-up.

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Laboratory and Field Measurements of Environmental Stratified Flows

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  1. Stellar Hydro Days, 26-28 July, 2006 Los Alamos Laboratory and Field Measurements of Environmental Stratified Flows Marko Princevac July 28, 2006

  2. Outline • Slope Flows • Entrainment in Katabatic Current • Eddy Diffusivity • Waves vs. Turbulence • Morning Inversion Break-up

  3. Synoptic flow Terrain induced flow Phoenix Slope Flows – Thermally Driven

  4. U T Q b vs. Upslope flow

  5. Thermal blob Detachment occurs when

  6. Competing tendencies B

  7. Water-Glycerin solution Heating System Critical angle experiment 10 < Pr < 10000

  8. Critical angle vs. Pr

  9. Katabatic (Downslope, Drainage) Flow H

  10. Downslope flow - Idealized Topography

  11. ACS –VTMX ASU Site

  12. Slope Site - VTMX

  13. Downslope flow – Field Results

  14. T=55 min Downslope flow - Pulsation

  15. } linearized , have oscillatory solution with the frequency or period Downslope flow - Pulsation

  16. T=55 min Downslope flow - Pulsation ACS b=4 deg: T=20 – 50 min SS b=1.8 deg: T=50 – 130 min

  17. Downslope flow - Entrainment Entrainment coefficient Richardson number

  18. Richardson Number Very stable Regime Non-turbulent Waves - very little turbulence Efficient Mixing -KH Regime Near Neutral

  19. Entrainment Entrainment velocities Entrainment coefficient Entrainment law

  20. Downslope flow – Laboratory Entrainment Turner (1986)

  21. Downslope flow - Entrainment

  22. Field data – 4 locations kilometer apart

  23. Downslope flow - Entrainment Turner (1986) - laboratory Field observations

  24. Downslope flow – Eddy diffusivities Eddy diffusivity of momentum Eddy diffusivity of heat High Re (107 – 108) Turbulent transport (u’w’, v’w’, w’q’…) dominates molecular (n,k)

  25. ACS Tower

  26. Wave Dominated Transport ? Downslope flow – Eddy diffusivities Molecular ~ 10-5 (m2s-1) Monti et al. 2002

  27. Waves vs. Turbulence

  28. Waves vs. Turbulence E E Frequency, Wave Number Frequency, Wave Number

  29. Waves also Waves also Waves also – generally (exception example: surface waves) Waves are essentially nondissipative Characteristics of Turbulent Flows - Irregularity, randomness - Diffusivity - Rotational - Dissipative

  30. Data Filtering

  31. Filters – low-pass E Low-pass filter unfiltered signal pass band transition band stop band f E pass-band ripples slope stop-band ripples cut off frequency f

  32. Butterworth Flattest Pass-band Steepest slope Smoothest transition Gain Gain Gain Bessel Elliptic Frequency Frequency Frequency Common Digital Filters

  33. Signal Spectra – where to cut? ? ?

  34. Shortest internalwave period Buoyancy frequency N corresponds to maximum possible wave frequency N= 0.05-0.1 rad/sec

  35. Cutting Frequency Period > 1 min Period < 1 min “waves” “turbulence”

  36. Filtering cut-off period of 1 minute 5 minute averaging 5 minute mean is subtracted before filtering Elliptical filter 1 min cut off

  37. KM from filtered and non-filtered data

  38. KH from filtered and non-filtered data

  39. TKE vs. “Wave” kinetic energy Non-filtered data Total KE (fluctuations) Filtered data “wave-less” KE (fluctuations) “Wave” KE = Total – Wave-less

  40. Rig=1

  41. Turbulent Prandtl Number (inversed)

  42. TKEfrom filtered and non-filtered data

  43. Nocturnal pooling

  44. Experimental setup

  45. Observed flow patterns Simple slope flow followed by recirculation Slope flow followed by recirculation plus layer “thickening” at the valley bottom Same as previous plus horizontal intrusions in stable core No large recirculation – all compensation of mass is via intrusions at different levels

  46. Combination of dimensionless parameters: b and Governing Parameters Slope Angle - b Initial Stability (stratification) - N Heat Flux (buoyancy flux) - qo Inversion Height - h

  47. Cold Pool Breakup Low B

  48. Cold Pool Breakup High B

  49. Flow dependence Low B regime High B regime Bc=1000-2000 Lower values for smaller slope angles

  50. Wheelers Farm 40o38’ N, 111o52’ W 1350 m MSL Wheeler Farm Site Wheeler Farm cross-section (40o38’ N) 2,223 m MSL 2,410 m MSL Inversion breakup in SLC valley

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