An Investigation into the Spatiotemporal Scale of Two Wind Ramp Events in Northeastern Colorado

A sudden surge or drop in wind speed, and consequently in wind power, over a brief period of time broadly defines a wind ramp (WR) event. Predicting the magnitude and timing of WR events is crucial for wind power integration into the electric grid. By exploring WR events, a better understanding of their characteristics can be acquired and later employed in wind energy forecasting. This research investigated the spatiotemporal evolution of the wind fields associated with two WR events, within a 48 hr. time period, by using a high-resolution observing network (7-surface stations at 10 m, 1-multilevel meteorological tower, and a wind profiler with 46 measurement heights). This network encircled a cluster of wind farms in northeastern Colorado. It was found that the WR events were associated with a mid-latitude cyclone that moved eastward from Montana. The first WR event was produced by a low-level jet (LLJ) which formed ahead of the cyclone and the second event was generated by the passage of a cold front (CF). The LLJ WR event featured a slow ramp up in the nighttime followed by a ramp down after sunrise when the LLJ weakened. The CF WR event ramped up rapidly with persistently strong winds at all heights. The two WR events also demonstrated very different wind profile characteristics in the lower 100 meters. The LLJ resulted in a highly sheared wind profile while the cold front resulted in a well-mixed layer. Overall, different and highly-variable characteristics were observed in each WR event. Further analyses are needed to understand the driving factors that lead to the observed spatiotemporal variations.