12 Jul 2023
 | 12 Jul 2023
Status: a revised version of this preprint is currently under review for the journal WES.

Brief communication: On the definition of the low-level jet

Christoffer Hallgren, Jeanie A. Aird, Stefan Ivanell, Heiner Körnich, Rebecca J. Barthelmie, Sara C. Pryor, and Erik Sahlée

Abstract. Low-level jets (LLJ) are examples of non-ideal wind speed profiles affecting wind turbine power production, wake recovery, and structural/aerodynamic loading. However, there is no consensus regarding which definition should be applied for jet identification. In this study we argue that a shear definition is more relevant for wind energy than a falloff definition. The shear definition is demonstrated and validated through development of an ERA5 LLJ climatology for six sites. Identification of LLJ and their morphology, frequency, and intensity is critically dependent on the i) vertical window of data from which LLJ are extracted and ii) the definition employed.

Christoffer Hallgren et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2023-74', Anonymous Referee #1, 19 Jul 2023
    • AC1: 'Reply on RC1', Christoffer Hallgren, 23 Aug 2023
  • RC2: 'Comment on wes-2023-74', Anonymous Referee #2, 30 Jul 2023
    • AC2: 'Reply on RC2', Christoffer Hallgren, 23 Aug 2023

Christoffer Hallgren et al.

Christoffer Hallgren et al.


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Short summary
Low-level jets (LLJ) are a special type of non-ideal wind profiles affecting both the wind energy production and the loads on the turbine. However, among LLJ researchers, there is no consensus regarding which definition to use to identify these profiles. In this work, we compare two different ways of identifying the LLJ – the falloff definition and the shear definition – and argue why the shear definition is better suited for wind energy applications.