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Baroclinicity and directional shear explain departures from the logarithmic wind profile



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  • Journal Title:
    Quarterly Journal of the Royal Meteorological Society
  • Personal Author:
  • NOAA Program & Office:
    CIMES (Cooperative Institute for Modeling the Earth System)
  • Description:
    Similarity and scaling arguments underlying the existence of a logarithmic wind profile in the atmospheric surface layer (ASL) rest on the restrictive assumptions of negligible Coriolis effects (no wind turning in the ASL) and vertically-uniform pressure gradients (barotropic atmospheric boundary layer, ABL). This paper alleviates these asymptotic arguments to provide a realistic representation of the ASL where the common occurrence of baroclinicity (height-dependent pressure gradients) and wind turning, traditionally treated as outer-layer attributes, take part in modulating the ASL. The approximation of a constant-stress ASL is first replaced by a refined model for the Reynolds stress derived from the mean momentum equations to incorporate the cross-isobaric angle (directional shear) and a dimensionless baroclinicity parameter (geostrophic shear). A model for the wind profile is then obtained from first-order closure principles, correcting the log-law with an additive term that is linear in height and accounts for the combined effects of wind turning and baroclinicity. Both the stress and wind models agree well with a suite of large-eddy simulations in the barotropic and baroclinic ABL. The findings provide a methodology for the extrapolation of near-surface winds to some 200 m in the near-neutral ABL for wind energy applications, the validation of the surface cross-isobaric angle in weather and climate models, and the interpretation of wind turning in field measurements and numerical experiments of the Ekman boundary layer.
  • Keywords:
  • Source:
    Quarterly Journal of the Royal Meteorological Society, 147(734), 443-464
  • DOI:
  • Document Type:
    Journal Article
  • Funding:
    Grant no. NA18OAR4320123
  • Rights Information:
    Other
  • Compliance:
    Submitted
  • Main Document Checksum:
    urn:sha256:f5ee125eb4be8eac1ce9f90346e9b6005fb98a2fe7719c7ac0a2de9ef2577392
  • Download URL:
  • File Type:
    Filetype[PDF - 4.23 MB ]
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