Vertical profiles of velocity variances and TKE using Doppler-lidar scan data

Vertical profiles of turbulence quantities have been traditionally very difficult to obtain above the region of the atmospheric boundary layer (ABL) sampled by towers. A technique for using vertical-slice-scan data from NOAA's High Resolution Doppler Lidar (HRDL), in which mean and variances of velocity data were calculated for vertically stacked, horizontally oriented bins, was employed during CASES-99 and described by Banta et al. 2002. Profiles of mean and variances of the along-wind (streamwise) component were obtained from scans in elevation oriented along the mean wind direction during two projects, CASES-99 and the Lamar Low-Level Jet Project near the town of Lamar, Colorado in September 2003. Both projects had tall towers and other instrumentation, against which to verify the HRDL profiles. CASES-99 had a 60-m tower instrumented at 5-m intervals with sonic anemometers, and Lamar had a 120-m tower instrumented at 4 levels (55, 67, 85 and 116 m) and a Doppler sodar.

Verification of the mean wind profile was straightforward, with highly correlated mean speeds among the lidar and other instruments independent of sampling strategies and averaging procedures. The variance estimates, on the other hand, proved highly sensitive to both the spatial and temporal averaging techniques and intervals employed. This paper will describe several series of averaging tests, and those procedures that were able to produce correlation coefficients of greater than 0.8 between tower and lidar measurements of the streamwise velocity variances.

Profiles of streamwise velocity variance have shown to be a surrogate for TKE profiles in the stable boundary layer. Such profiles are not well known and are important for further understanding of turbulent mixing processes below low–level jet.