Internal Boundary Layer Structure Observed by dual-Doppler Lidar

Observations from two scanning coherent Doppler lidars, as well as a network of surface in-situ sensors are used to investigate the structure of boundary layer flows over the central Washington DC area. Dual-Doppler lidar analysis is applied to generate highly resolved vertical cross sections of the flow over the Potomac River and the adjacent urban shoreline. These results are used to study the structure of the internal boundary layers that develop as the flow advects over the transition from urban land surface to water. The data used in this study were acquired during a major field campaign in May 2004. As part of that field campaign, one Doppler lidar was deployed near Arlington National Cemetery, and a second system was deployed on the east bank of the Potomac River, at Bolling Air Force Base. Both systems performed repeated volume scans throughout the duration of the two week field campaign. The proximity of the lidars offered a unique opportunity to observe internal boundary layer development over the Potomac River. Quantities derived from the dual-Doppler analysis include hourly averaged horizontal velocity components and variances. The data processing methods incorporate error propagation as well as clutter rejection. Changes in the mean velocity and variance profiles with fetch and atmospheric stability are examined. Preliminary analysis of these results indicates that under certain stability conditions the river has a pronounced effect on the mean flow and velocity variance.