Measurements of small-scale turbulence made over the complex-terrainatmospheric boundary layer during the MATERHORN Program are used to describethe structure of turbulence in katabatic flows. Turbulent and meanmeteorological data were continuously measured at multiple levels at fourtowers deployed along the East lower slope (2-4 deg) of Granite Mountain. Themulti-level observations made during a 30-day long MATERHORN-Fall fieldcampaign in September-October 2012 allowed studying of temporal and spatialstructure of katabatic flows in detail, and herein we report turbulence andtheir variations in katabatic winds. Observed vertical profiles show steepgradients near the surface, but in the layer above the slope jet the verticalvariability is smaller. It is found that the vertical (normal to the slope)momentum flux and horizontal (along the slope) heat flux in a slope-followingcoordinate system change their sign below and above the wind maximum of akatabatic flow. The vertical momentum flux is directed downward (upward)whereas the horizontal heat flux is downslope (upslope) below (above) the windmaximum. Our study therefore suggests that the position of the jet-speedmaximum can be obtained by linear interpolation between positive and negativevalues of the momentum flux (or the horizontal heat flux) to derive the heightwhere flux becomes zero. It is shown that the standard deviations of all windspeed components (therefore the turbulent kinetic energy) and the dissipationrate of turbulent kinetic energy have a local minimum, whereas the standarddeviation of air temperature has an absolute maximum at the height ofwind-speed maximum. We report several cases where the vertical and horizontalheat fluxes are compensated. Turbulence above the wind-speed maximum isdecoupled from the surface, and follows the classical local z-less predictionsfor stably stratified boundary layer.
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