Variations in Parametric Sensitivity for Wind Ramp Events in the Columbia River Basin

Abstract

This work investigates the sensitivity of wind speed forecasts during wind ramp events to parameters within a numerical weather prediction model boundary layer physics scheme. In a novel way, it explores how these sensitivities vary across 1) ensemble members with different initial conditions, 2) different times during the events, 3) different types of ramp-causing events, and 4) different horizontal grid spacing. Previous research finds that a small number of parameters in the surface layer and boundary layer schemes are responsible for the majority of the forecast uncertainty. In this study, the values of parameters within the Mellor–Yamada–Nakahishi–Niino (MYNN) boundary layer scheme and the MM5 surface layer scheme of the Weather Research and Forecasting (WRF) Model are perturbed in a systematic way to evaluate parametric sensitivity for two types of specific ramp-causing phenomena: marine pushes and stable mix-out events. This work is part of the Department of Energy’s Second Wind Forecast Improvement Project (WFIP2). A major finding of this study is that there are large differences in parametric sensitivity between members of the same initial condition ensemble for all cases. These variations in sensitivity are the result of differences in the atmospheric state within the initial condition ensemble, and the parametric sensitivity changes over the course of each forecast. Finally, parametric sensitivity changes between event type and with model resolution. These conclusions are particularly relevant for future sensitivity studies and efforts at model tuning.

Local thermal gradient and large-scale circulation impacts on turbine-height wind speed forecasting over the Columbia Basin

“…The elevation of the CRG is very near sea level, compared to the Cascade passes, whose lowest elevation is 900 m (Sharp and Mass, 2004). Thus, the CRG serves as a primary pathway for the intrusion flows into the basin (Smith and Ancell, 2019). Observational studies show that flows frequently originate west of the Cascade ranges, propagate through the CRG (Banta et al, 2020), and move eastward through the basin (Brewer and Mass, 2014).…”

“…They found that the perturbation of IC produced a larger ensemble spread than application of different PBL schemes, indicating that changes (errors) in IC can lead to large uncertainties in wind flow forecasts. Smith and Ancell (2019) further reported considerable differences in the results of parametric sensitivity among the ensembles started from different ICs. By characterizing NWP model forecasting errors using doppler-lidar measurements over the Columbia River Basin, Banta et al (2020) suggested that the forecasting errors could be imported from upstream or generated locally at an earlier time, which emphasized the impacts of both local thermal gradient and large-scale circulation initial status on wind forecast.…”

“…resolution, model physics, initial/boundary conditions, and parameterizations of the sub-grid processes (e.g., Yang et al, 2013Yang et al, , 2017Yang et al, , 2019Qian et al, 2015;Siuta et al, 2017a;Berg et al, 2019Berg et al, , 2021Smith and Ancell, 2019), which ultimately influences forecasts of wind power (Banta et al, 2013(Banta et al, , 2018. The uncertainties associated with the model initialization decreases the reliability of the deterministic forecasts and can have serious financial consequences (Marquis et al, 2011).…”

“…In particular, we focus on two typical summer weather systems associated with a local thermal gradient and large-scale cold frontal passage. Extensive efforts have been made to develop scale-adaptive physical parameterizations and parameter optimization during the Second Wind Forecast Improvement Project (WFIP2; Olson et al, 2019b;Shaw et al, 2019;Wilczak et al, 2019), but there has been less attention to the impact of ICs on the forecast skill (Smith and Ancell, 2019). The WFIP2-optimized NWP model is used in this study.…”

Reply to reviewers on wes-2021-72

“…Furthermore, the composite analyses and cross-section (Sharp and Mass, 2004). Thus, the CRG serves as a primary pathway for the intrusion flows into the basin (Smith and Ancell, 2019). Observational studies show that flows frequently originate west of the Cascade ranges, propagate through the CRG (Banta et al, 2020), and move eastward through the basin (Brewer and Mass, 2014).…”