Flux-gradient relation and atmospheric wind profiles — an exploration using WRF and lidars

Pedro Santos*, Alfredo Peña, Jakob Mann

*Corresponding author for this work

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Abstract

A common closure for the planetary boundary layer in numerical weather models assumes a direct relation between turbulent fluxes and the mean wind vertical gradient, i.e., the flux-gradient relation or K-theory. This assumption implies that the angle β between the momentum stress vector and the mean gradient of the velocity vector are aligned, i.e., β = 0°. This is not what we observe from measurements. We quantify the misalignment of β in offshore conditions using measurements from a long-range Doppler profiling lidar and numerical simulations from the New European Wind Atlas mesoscale model output. We compare vertical profiles of wind speed, wind direction, momentum fluxes, and β up to 500 m, hence covering the rotor areas of modern offshore wind turbines and beyond. The results show that β ≈ −18° on average, with a lower, but still non-zero, value under stable stability conditions, ≈ −7°. We illustrate that the simulations describe well the mean wind speed and momentum fluxes within the observed levels, but the characterization of wind turning effects could be improved.
Original languageEnglish
Article number8
Book seriesJournal of Physics: Conference Series
Volume1618
Issue number3
Number of pages32,032
ISSN1742-6596
DOIs
Publication statusPublished - 2020
EventTORQUE 2020 - Online event, Netherlands
Duration: 28 Sep 20202 Oct 2020
https://www.torque2020.org/

Conference

ConferenceTORQUE 2020
LocationOnline event
Country/TerritoryNetherlands
Period28/09/202002/10/2020
Internet address

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