Observations of wind ramps generated by thunderstorm outflows

Abstract. Thunderstorms occur frequently in regions with strong wind resources, such as the U.S. Great Plains. The outflows from these storms generate wind ramps, where the wind speed and direction change dramatically over a short period. Wind turbines are designed to withstand wind ramps such as the "extreme coherent gust with direction change" (ECD) defined by the International Electrotechnical Commission (IEC), but this depiction is highly simplified and based on point measurements. In the current investigation, we characterize the wind ramps generated by six thunderstorm outflows observed in northern Oklahoma using dual-Doppler X-band radar measurements covering a 160 km³ volume, and compare their properties with the IEC-defined ECD. We show that, while the observed wind ramps exhibit wind speed and direction changes with similar magnitudes to the ECD, the observed rise times are an order of magnitude longer. Furthermore, the observed events are more complex than the idealized ECD profile, displaying spatial and temporal variations that cause significant variability in wind turbine power generation.