Capabilities of Scanning Lidar Systems to Measure Surface Layer Profiles of Humidity, Temperature and Wind

One weakness of today's weather and climate models is the inaccurate representation and parameterization of the boundary layer processes and land-atmosphere feedback. In order to investigate these processes, scanning lidar systems allow the observation of surface layer profiles of humidity, temperature and wind velocity. In August 2017, the Land-Atmosphere Feedback Experiment (LAFE) was organized at the Atmospheric Radiation Measurements (ARM) Program Southern Great Plains site in Oklahoma, USA, with the deployment of a novel scanning lidar synergy. A combination of Doppler lidars, Raman lidars, and a differential absorption lidar was used to measure the wind velocity, humidity, and temperature from the land-surface through the ABL. With specific coordinated scans not only vertical profiles above one point were captured but also 2-dimensional fields of wind, humidity, and temperature. During intensive observations periods, a coordinated scan pattern with consecutive low elevations and full RHI scans was applied by all lidar instruments. For 50 mins out of every hour, the Doppler lidars performed intersecting RHI scans at four flux tower locations to create high vertical resolution (approx. 3 m) wind profiles from very close to the surface to 100 m above ground. The scanning temperature and water vapor lidars measured the same vertical range with high-resolution RHI scans. For the remaining 10 min, the Doppler lidars performed PPI scans to capture the horizontal wind field, while the scanning temperature and water vapor lidars performed full RHI scans to capture the full extent of the ABL. By combining their profiles, further quantities like surface sensible and latent heat fluxes can be derived and turbulent to mesoscale structures were detected. The collected data set will allow detailed studies of land-atmosphere feedback processes as well as comparisons with model output.

In this contribution we will present first results of the 3-D scanning water vapor differential absorption lidar (DIAL), of the scanning temperature Raman lidar (TRRL), and of scanning Doppler lidars (DL) revealing complex 2-D structures of the surface layer and throughout the ABL. Additionally, an estimation of fluxes can be obtained by using the combination of the quantities humidity, temperature and wind velocity. These results may question the applicability of Monin-Obukhov similarity theory in heterogeneous land use.