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

Abstract:

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 the Weather Research and Forecasting (WRF) model. Thus, developing the capability to measure dissipation rates in the PBL will allow for identification of weaknesses in, and improvements to the parameterizations.

We use data from a 915-MHz wind profiling radar at the Boulder Atmospheric Observatory, collected during the XPIA campaign in spring 2015, to identify the critical parameters for measuring eddy dissipation rates using the spectral width method. 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 power spectrum for measuring spectral widths for use in the computation of the eddy dissipation rates. These estimates are compared to six heights of turbulence-measuring sonic anemometers from 50 – 300 m on a co-located 300 m tower as verification, showing encouraging results. These methods are then applied to the wind profiling radar data being collected in 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. This campaign uses of a suite of field observations, including many wind profiling radars, in the Columbia River Gorge, a location with complex terrain where turbulence parameterizations are critical for wind energy prediction.