On quantifying waves and turbulence contributions to momentum and buoyancy transports in katabatic flows

The katabatic currents, as an archetype of the stably stratified flow, are known to sustain intense wave activity and intermittent turbulence. Turbulence is very efficient mechanism for momentum and heat transport. On the other hand, linear or weakly non-linear waves are efficient in transporting the momentum but they are known to be very inefficient in transporting the heat. An attempt was made to separate turbulent transports of momentum and heat from those corresponding to waves. Nighttime data collected on the slopes during VTMX 2000 campaign was used. Elliptical Filters of the third and fourth order were used to extract waves with periods ranging from one minute to thirty minutes. The Elliptic filter (also known as a Cauer response) was chosen owing to its very steep attenuation characteristic. This steep cutoff allowed precise selection of the signal of interest. Transport efficiency was quantified through the eddy viscosity type coefficients. Coefficients obtained using filtered (approximate "wave less") data are compared to the unfiltered (waves and turbulence) one.