Spatiotemporal visualization of wind turbulence from measurements by a Windcube 200s lidar in the atmospheric boundary layer

Abstract

The results of spatiotemporal visualization of the kinetic energy of turbulence, its dissipation rate, and integral scale of turbulence from measurements by a Windcube 200s lidar with the use of the conical scanning by the probing beam in the atmospheric boundary layer are presented. When evaluating the parameters of wind turbulence, the lidar data filtering procedure was applied. This procedure allows obtaining acceptable results with a non-zero probability of bad estimate of the radial velocity.

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“…While the 75 • -scans can also be used to retrieve turbulence kinetic energy dissipation rate, an elevation angle of 35.3 • is necessary to derive turbulent kinetic energy, integral length scale and momentum fluxes according to Smalikho and Banakh (2017). As described in Stephan et al (2018b), boundary-layer height can be estimated 20 through detection of the height at which the eddy dissipation rate (EDR) drops below a value of 10 −4 m 2 s −3 . As an example, of wind speed retrievals with the FSWF-method depends on the signal-to-noise ratio of line-of-sight velocity measurements (Stephan et al, 2018a).…”

Towards improved turbulence estimation with Doppler wind lidar VAD scans

“…Improvements of turbulence estimates in low signal conditions can be achieved with filtering of bad estimates as described in Stephan et al (2018). This approach is not based on the calculation of the azimuth structure function from measured radial wind speeds, but uses probability density functions (PDFs) and their corresponding standard deviations.…”

“…Measured PDFs of the variables v r (R, θ), ∆v r (R, θ + ∆θ) and ∆v r (R, θ + l∆θ) are fit to the model PDFs to obtain an estimation of the corresponding standard deviations σ 1 , σ 2 and σ 3 and probability of bad estimates P 1 , P 2 and P 3 . However, since the PDFs cannot be assumed Gaussian in atmospheric turbulence, the standard deviations are finally calculated as the integral over the measured PDFs in the range ±3.5σ according to Stephan et al (2018).…”

“…At an elevation angle of 35.3 • , a VAD scan allows to retrieve TKE, its dissipation rate, integral length scale and momentum fluxes according to a method that was first developed for radar by Kropfli (1986) and adapted for lidar later by Eberhard et al (1989) using the variance of radial velocities along the scanning cone. Further improvements of this method have been implemented by Smalikho and Banakh (2017) and Stephan et al (2018), which also account for lidar volume averaging effects. For conditions with significant advection, the method is not applicable and causes large errors, especially at low altitudes where the cone diameter of the VAD scan is small.…”

Reply to referee comment #1

“…A first guess of the standard deviations is needed to find the ±3.5σ region for the integral over the PDF. All the details of this method are given in Stephan et al (2018). Since this method is not essential for this study, we do not want to expand too much on it in this manuscript.…”