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

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

Slope Flows – Thermally Driven Phoenix Terrain induced flow Synoptic flow

Upslope flow T U Q  vs.

Thermal blob Detachment occurs when

Competing tendencies B

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

Critical angle vs. Pr

Katabatic (Downslope, Drainage) Flow H

Downslope flow - Idealized Topography

ACS –VTMX ASU Site

Slope Site - VTMX

Downslope flow – Field Results

Downslope flow - Pulsation T=55 min

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

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

Downslope flow - Entrainment Entrainment coefficientRichardson number

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

Entrainment Entrainment velocities Entrainment coefficient Entrainment law

Downslope flow – Laboratory Entrainment Turner (1986)

Downslope flow - Entrainment

Field data – 4 locations kilometer apart

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

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 (  )

ACS Tower

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

Waves vs. Turbulence

Frequency, Wave Number EE

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

Data Filtering

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

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

Signal Spectra – where to cut? ? ?

Shortest internalwave period Buoyancy frequency N corresponds to maximum possible wave frequency N= rad/sec

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

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

K M from filtered and non-filtered data

K H from filtered and non-filtered data

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

Rig=1

Turbulent Prandtl Number (inversed)

TKE from filtered and non-filtered data

Nocturnal pooling

Experimental setup

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

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

Cold Pool Breakup Low B

Cold Pool Breakup High B

Flow dependence Low B regime High B regime B c = Lower values for smaller slope angles AngleB min B max 10 o o o

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

Expected Cold Pool Destruction for SLC

Summary - Upslope flow - Downslope flow velocity

Summary - Downslope flow periodicity - Entrainment

Summary - Inversion breakup mechanisms - Eddy diffusivity

Next Scale

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

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

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

Friction velocity: filtered and non-filtered

Normalized momentum flux

Temperature scale

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

Downslope flow – Normalized Eddy diffusivities