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

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

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

4. Upslope flow T U Q  vs.

5. Thermal blob Detachment occurs when

6. Competing tendencies B

7. Critical angle experiment Heating System Water-Glycerin solution 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. Downslope flow - Pulsation T=55 min

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

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

17. Downslope flow - Entrainment Entrainment coefficientRichardson number

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

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 (10 7 – 10 8 ) Turbulent transport (u’w’, v’w’, w’  ’…) dominates molecular (  )

25. ACS Tower

26. Downslope flow – Eddy diffusivities Wave Dominated Transport ? Monti et al. 2002 Molecular ~ 10 -5 (m 2 s -1 )

27. Waves vs. Turbulence

28. Frequency, Wave Number EE

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

30. Data Filtering

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

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

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 “waves”“turbulence” Period > 1 minPeriod < 1 min

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. K M from filtered and non-filtered data

38. K H 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. TKE from 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. Governing Parameters Initial Stability (stratification) - N Slope Angle -  Heat Flux (buoyancy flux) - q o Inversion Height - h Combination of dimensionless parameters:  and

47. Cold Pool Breakup Low B

48. Cold Pool Breakup High B

49. Flow dependence Low B regime High B regime B c =1000-2000 Lower values for smaller slope angles AngleB min B max 10 o 1072497 20 o 2128198 30 o 245564

50. Inversion breakup in SLC valley Wheeler Farm cross-section (40 o 38’ N) Wheelers Farm 40 o 38’ N, 111 o 52’ W 1350 m MSL Wheeler Farm Site 2,410 m MSL 2,223 m MSL

51. Expected Cold Pool Destruction for SLC

52. Summary - Upslope flow - Downslope flow velocity

53. Summary - Downslope flow periodicity - Entrainment

54. Summary - Inversion breakup mechanisms - Eddy diffusivity

55. Next Scale

56. Filters – ideal f E unfiltered signal “Brick-wall” filter (hypothetical ideal filter) Low-pass example f E cut off frequency

57. Filters – high-pass f E High-pass filter stop bandtransition band pass band slope cut off frequency stop-band ripples pass-band ripples f E unfiltered signal

58. Filters – pass-band & stop-band Pass-band filter f E unfiltered signal f E pass- band width cut off frequency Stop-band filter f E stop- band width cut off frequency

59. Friction velocity: filtered and non-filtered

60. Normalized momentum flux

61. Temperature scale

62. Summary - Removing “waves” decreases momentum transport (K M ) for high Ri g - Removing “waves” does not affect heat transport (K H )

63. Downslope flow – Normalized Eddy diffusivities