24SMOI Winds over DC

Atmospheric Transport and Dispersion models (AT&D) such as the EPA’s Regulatory Model (AERMOD) model and DOE’s Health Physics modeling code HotSpot use either atmospheric power-law

or atmospheric normalized log-law techniques to establish velocity profiles through the lowest part of the

atmospheric boundary layer referenced as the atmospheric surface layer (ASL). For example, these developed vertical profiles of mean wind speed are used to extrapolate either observed or numerical model predictions of wind speed to estimate particle transport velocities through the ASL or determine exhaust stack emission parameters such as stack downwash or effective plume rise.

NOAA/ARL has maintained, since 2004, a meteorological measurement system on the rooftop of the US Department of Commerce Herbert Hoover Building (HCHB) at the central point within the National Capital region. The HCHB monitoring station is part of the DCNet research network established and operated by NOAA/ARL since 2003 to collect a large database of meteorological measurements in Washington, D.C. NOAA/CSL has recently, in 2022, installed a wind lidar on the rooftop of the HCHB station. The combination of NOAA/ARL’s HCHB momentum and heat flux station and NOAA/CSL’s Lidar wind velocity profiler located on the rooftop of HCHB station provides a unique opportunity to explore the dynamics of the atmospheric planetary boundary layer over a major Eastern US metropolitan area. Lidar observations covered the period April-May, 2021 and March-December, 2022; DCNet flux observations were available for March-December, 2022.

The data collected from the NOAA/CSL’ wind lidar, has provided the opportunity to evaluate the accuracy previously implemented vertical profiling techniques based on observed surface values. This abstract discusses the results from application of the atmospheric log-law technique and statistical evaluation of predicted and observed wind speeds at 100m above the local displacement height.

Lidar profiles were used to define both the mean zero-plane displacement (d) and mean surface roughness (z₀) heights for the HCHB observation site. These parameters were coupled with observed values of shear stress to predict wind velocities at 100m above the displacement height. A second trial was conducted with the same parameter set with the exception that estimated values of surface roughness from the NOAA/ARL flux tower were evaluated.

The results show that using a fixed value of 0.5m for surface roughness yielded a mean absolute error of 1.14 m/s and mean absolute relative error of 0.332. Allowing a varying surface roughness yields a mean error of 1.009 m/s and a mean absolute relative error of 0.257. Based on these results, we can conclude that the application of Logarithmic Wind Law technique, within the urban core of the national Capital Region, demonstrated reasonable wind speed agreement through the atmospheric surface layer.