Measurements of Velocity Variance and Turbulence Dissipation Rates in the Planetary Boundary Layer from Wind Profiling Radars

When forecasting winds at a wind plant for energy production, the turbulence parameterizations are crucial for understanding wind plant performance. Recent research shows that the turbulence (eddy) dissipation rate in planetary boundary layer (PBL) parameterization schemes introduces significant uncertainty in Weather Research Forecasting (WRF) models. Thus, developing the capability to measure dissipation rates will allow for identification of weaknesses in, and improvements to the PBL parameterization schemes. We use data from 449- and 915-MHz wind profiling radars at the Boulder Atmospheric Observatory, collected during the XPIA campaign in Spring 2015 to identify the critical parameters for measuring vertical velocity variance and eddy dissipation rates using first and second moments (shift and spectral width) of high temporal resolution vertical velocity Doppler spectra. Radar set-up parameters (e.g., spectral resolution), post-processing techniques (e.g., filtering for non-atmospheric signals), and spectral averaging are optimized to capture the most accurate spectra for measuring first and second moments for use in the computation of the variance and dissipation rates. These estimates are compared to six heights of sonic anemometers from 50 – 300m on a co-located tall tower as verification, resulting in high correlations with accepted methods of calculating variance and inertial-range dissipation from sonic anemometers. The radar set-up parameters and post-processing methods are then applied to the 915-MHz wind profiling radar at Wasco, OR during the Wind Forecasting Improvement Project 2 (WFIP2), a DOE funded campaign that aims to improve the ability to forecast hub-height winds from WRF-based models. These observational profiles of turbulence dissipation rates will be valuable for improving the PBL parameterization schemes.