The Effects of Wind Farm Wakes on Freezing Sea Spray in the Mid-Atlantic Offshore Wind Energy Areas

Abstract. The U.S. is expanding its wind energy fleet offshore where winds tend to be strong and consistent. In the mid-Atlantic, strong winds, which promote heat transfer and wind-generated sea spray, paired with cold temperatures can cause ice on equipment when plentiful moisture is available. Near-surface icing is induced by a moisture flux from sea spray, which poses a risk to vessels and crews. Ice accretion aloft occurs when liquid precipitation is present and can reduce turbine blade performance and introduce extra load and fatigue on the turbine. Thus, it is crucial to understand the icing hazard across the mid-Atlantic. We analyze Weather Research and Forecasting model numerical weather prediction simulations at coarse temporal resolution over a 20-year period to assess freezing events over the long-term record and at finer granularity over the 2019–2020 winter season to identify the post-construction turbine impacts. Over the 2019–2020 winter season, results suggest that sea-spray–induced icing can occur up to 66 hours per month at 10 m at higher latitudes. Freezing events during this season typically occur during cold air outbreaks, which are the introduction of cold continental air over the warmer maritime surface and last a total duration of 253 hours. Over the 20-year period, all cold air outbreak events coincide with freezing conditions, although not all freezing events are cold enough to signify a cold air outbreak. Further, we assess the impacts of wind plant installation on icing using the fine-scale simulation data set. Wakes from large wind plants reduce the wind speed, which mitigates the chance for freezing. Conversely, the near-surface turbine-induced introduction of cold air in frequent wintertime unstable conditions enhances the risk for freezing. Overall, the turbine–atmosphere interaction causes a net mitigation of freezing hours within the wind plant areas, with a reduction up to 17 hours at 20 m in January 2020.