Analysis of Doppler Lidar Data Acquired During the Pentagon Shield Field Campaign

Observations from two coherent Doppler lidars deployed during the Pentagon Shield field campaign are analyzed in conjunction with other sensors to characterize the overall boundary-layer structure, and identify the dominant flow characteristics during the entire two-week field campaign. Convective boundary layer CBL heights and cloud base heights CBH are estimated from an analysis of the lidar signal-to-noise-ratio SNR, and mean wind profiles are computed using a modified velocity-azimuth-display VAD algorithm. Three-dimensional wind field retrievals are computed from coordinated overlapping volume scans, and the results are analyzed by visualizing the flow in horizontal and vertical cross sections. The dual-Doppler analysis technique used in this study makes use of hourly averaged radial velocity data to produce three-dimensional grids of the horizontal velocity components, and the horizontal velocity variance. Visualization of horizontal and vertical cross sections of the dual-Doppler wind retrievals often indicated a jet-like flow feature over the Potomac River under southerly flow conditions. This linear flow feature is roughly aligned with the Potomac River corridor to the south of the confluence with the Anacostia River, and is most apparent at low levels i.e. below 150 m MSL. It is believed that this flow arises due to reduced drag over the water surface and when the large scale flow aligns with the Potomac River corridor.