Low-level jets are a common phenomenon in the Finnish archipelago area and occur most often during spring and summer. For wind energy, low-level jets are important phenomena to understand; the wind shear associated with the jet can be harmful for wind turbines, but the enhanced wind speeds related to the jet maximum can increase wind power production.
A low level jet (LLJ) is a local wind speed maximum observed in the vertical profile of the horizontal wind speed that typically occurs in the lowest 1500 meters above ground level. An algorithm for identifying LLJs was created and applied to over two years of Doppler lidar wind profile data to investigate LLJ occurrence and properties over Utö, a small island in the Finnish archipelago. Low-level jets often occur below 150 m at Utö, which means that they can have a significant impact on wind power production. It was found that more low-level jets occur during spring and summer months, and that most of these are lower than those observed during winter time. The mean LLJ wind speed was
11.6 m s-1.
Low-level jets are not always captured well by numerical models and, therefore, their effect on the true wind climate should be verified, especially if the wind power production capacity is expected to increase in the archipelago area. "The wind shear was shown to be usually stronger closer to the ground below the jet than above the jet, and therefore, LLJs should be taken into account when planning new wind farms in the Finnish coastal areas", says researcher Minttu Tuononen.
The LLJ identification algorithm created in the study can be applied to other operational Doppler lidars to enable near-real time LLJ monitoring.
Researcher Minttu Tuononen, phone: +358 50 344 8187, email@example.com
Reference: Tuononen, M., E.J. O'Connor, V.A. Sinclair, and V. Vakkari, 2017: Low-Level Jets over Utö, Finland, Based on Doppler Lidar Observations. J. Appl. Meteor. Climatol., 56, 2577–2594, https://doi.org/10.1175/JAMC-D-16-0411.1
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