Toward Understanding Low Level Jet Climatology over West Texas and its Impact on Wind Energy

Abstract

Low Level Jets (LLJs) are defined as regions of relatively strong winds in the lower part of the atmosphere. They typically occur between 100 and 1500 m above ground level (ABL) and can be found in every continent. In particular, LLJs are a common feature over the Great Plains in the United States. It has been reported that 75% of LLJs in the Great Plains occur at night and with seasonal patterns. Our preliminary results have corroborated some of the LLJ known characteristics, but also shown the lack of a clear three-dimensional picture of how the phenomenon is displaced over West Texas (precise location, timing and lifespan). This paper is focused on the development of a detailed LLJ climatology and its weather correlates for West Texas. Using the 200-m tower data (Reese, Texas), profiler and Mesonet data, and WRF runs, a 4-dim model is introduced which summarizes the main features of the LLJ over the aforementioned region and shows its patterns along the year. Furthermore, we also demonstrate the importance of LLJs for wind energy production. It has been observed that during a LLJ event the level of turbulence intensities and TKE are significantly much lower than those during unstable conditions; as a result, cyclical aerodynamic loads on turbine blades are diminished. The major salient results from this study include: the vertical shears in LLJs are very large, causing higher static loads. Finally, the WRF model has accurately captured the beginning of the LLJ event; however, the local maximum wind speed at the LLJ "nose" has been under-predicted by approximately 15%, which highlights the difficulties WRF still faces in predicting this phenomenon.