Environmental Fluid Mechanics

, Volume 14, Issue 2, pp 431–450 | Cite as

Waves and turbulence in katabatic winds

  • P. Monti
  • H. J. S. Fernando
  • M. Princevac
Original Article


The measurements taken during the Vertical Transport and Mixing Experiment (VTMX, October, 2000) on a northeastern slope of Salt Lake Valley, Utah, were used to calculate the statistics of velocity fluctuations in a katabatic gravity current in the absence of synoptic forcing. The data from ultrasonic anemometer-thermometers placed at elevations 4.5 and 13.9 m were used. The contributions of small-scale turbulence and waves were isolated by applying a high-pass digital (Elliptical) filter, whereupon the filtered quantities were identified as small-scale turbulence and the rest as internal gravity waves. Internal waves were found to play a role not only at canonical large gradient Richardson numbers \((\overline{\hbox {Ri}_\mathrm{g} } >1)\), but sometimes at smaller values \((0.1 < \overline{\hbox {Ri}_\mathrm{g}}<1)\), in contrast to typical observations in flat-terrain stable boundary layers. This may be attributed, at least partly, to (critical) internal waves on the slope, identified by Princevac et al. [1], which degenerate into turbulence and help maintain an active internal wave field. The applicability of both Monin-Obukhov (MO) similarity theory and local scaling to filtered and unfiltered data was tested by analyzing rms velocity fluctuations as a function of the stability parameter z/L, where L is the Obukhov length and z the height above the ground. For weaker stabilities, \(\hbox {z/L}<1\), the MO similarity and local scaling were valid for both filtered and unfiltered data. Conversely, when \(\hbox {z/L}>1\), the use of both scaling types is questionable, although filtered data showed a tendency to follow local scaling. A relationship between z/L and \(\overline{\hbox {Ri}_\mathrm{g} }\) was identified. Eddy diffusivities of momentum \(\hbox {K}_\mathrm{M}\) and heat \(\hbox {K}_\mathrm{H}\) were dependent on wave activities, notably when \(\overline{\hbox {Ri}_\mathrm{g} } > 1\). The ratio \(\hbox {K}_{\mathrm{H}}/\hbox {K}_{\mathrm{M}}\) dropped well below unity at high \(\overline{\hbox {Ri}_\mathrm{g} }\), in consonance with previous laboratory stratified shear layer measurements as well as other field observations.


Katabatic winds Mixing Stratified flows MOST Eddy diffusivity 



The data analysis was performed with the support of Office of Naval Research Award # N00014-11-1-0709, Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program.


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Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  1. 1.Dipartimento di Ingegneria Civile, Edile e AmbientaleUniversità degli Studi di Roma “La Sapienza”RomeItalia
  2. 2.Department of Civil and Environmental Engineering and Earth SciencesThe University of Notre DameNotre DameUSA
  3. 3.Department of Mechanical EngineeringUniversity of CaliforniaRiversideUSA

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