The share of the mean turbulent kinetic energy in the near-neutral surface layer for high and low wind speeds

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We examine the dependence on wind speed of the share of the mean turbulent kinetic energy among the three velocity components in the near-neutral surface layer. To contrast the general behaviour and the local effects, four datasets are considered, corresponding to different surfaces and environmental conditions. For high wind speeds (i.e., wind speed ≈ 10 ms^(−1)), the shares are well-defined and about the same for all sites. As wind speed decreases (becoming ≈ 1 ms^(−1)), large record-to-record variability occurs giving, on average, an almost isotropic state for the horizontal velocity components. Through spectral analysis, we relate this behaviour to the low-frequency, submeso motions and to the lack of conditions required by Reynolds averaging. The implications for modelling are also discussed, showing that the wind speed, or a related quantity, must be accounted for, besides stability, in second-order closures.
© Springer Nature B.V. 2019. Thanks are due to: the SABLES98 team, Prof. J.L. Casanova (Director of CIBA), and Dr. J. Peláez (for his technical support); the Korean Polar Research Institute (KOPRI), in particular Dr. T. Choi, that provided CSAT3 CCT sonic data. CY has been funded by the Spanish Government, under MINECO projects CGL2015-65627-C3-3-R (MINECO/FEDER) and CGL2016-81828-REDT.