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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