School of Meteorology (Defense)

Vertical Velocity Turbulence Profiles Measured by 2 Horizontally Separated Doppler Lidars

Nathan Anderson
OU School of Meteorology

04 August 2014, 12:00 PM

National Weather Center, Room 5820
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Two identical Doppler Lidars were deployed at the Atmospheric Radiation Measurement’s Southern Great Plains (ARM SGP) site for three different experiments in 2010, 2012 and 2013. Profiles of the 2nd (variance) and 3rd moment of the vertical velocity, along with skewness, which together help describe the turbulence in the boundary layer, were derived from time-series of Doppler wind measurements when the lidars were pointed vertically. The two lidars were separated by 300 m, and data from these systems were analyzed to derive turbulence profiles during afternoon periods with a quasi-stationary boundary layer. Lidar outputs of vertical velocity and attenuated backscatter were used to calculate the convective boundary layer height (zi) and profiles of turbulence statistics (variance and skewness), while utilization of Plan Position Indicator scans and the Velocity Azimuth Display technique allowed for the calculation of vertical profiles of wind speed and direction.

A total of 102 mid-day case selections were made when the convective boundary layer height was constant and not impacted by synoptic disturbances. In the majority of the cases, the profiles of variance and skewness between the horizontally separated lidars were in good agreement; however, there were a small number of cases where 1 or both profiles (variance and/or skewness) disagreed. Surface fluxes, wind conditions, friction velocity, integral time scale, and the convective velocity scale were used to understand the observed differences in variance and skewness profiles from the two lidars. Of the variables examined, it was discovered that low wind speeds, low friction velocity, and large integral time scales were best correlated with larger variance and skewness profile differences between lidars.

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