How to design single-column model experiments for comparison with observed nocturnal low-level jets

P. Baas, F.C. Bosveld, G. Lenderink, E. van Meijgaard, A.A.M. Holtslag

Research output: Contribution to journalArticleAcademicpeer-review

36 Citations (Scopus)

Abstract

Single-column models (SCMs) are widely employed to evaluate boundary-layer parametrizations under well-controlled conditions. To compare SCM results to observations, these models must be driven by realistic forcings of the three-dimensional (3D) atmospheric state. However, these forcings are inherently uncertain. The central research question is therefore: can observations be used to distinguish between different parametrization schemes in SCM simulations or is the spread due to uncertainties in the forcings too large? This study investigates this question for the nocturnal low-level jet (LLJ) at Cabauw. First, we analyse a single LLJ case that has been used for the third GEWEX Atmospheric Boundary Layer Studies (GABLS3) intercomparison study. To estimate the forcings, for this case a blend of local observations and 3D model output has been used. A sensitivity study to both the forcings and the turbulence formulation is performed by using the SCM version of the ECMWF model. The sensitivity to the turbulence parametrization is largest in the bulk of the stable boundary layer (SBL). The influence of the forcings manifests itself mainly in the upper part of the SBL and above. Second, an ensemble of eight comparable LLJ cases is considered. Using forcings derived from 3D model integrations, SCM results of the separate cases show significant deviations from the observations. However, the mean of the SCM simulations agrees well with the mean of the observations. Based on the eight selected LLJ cases, a composite SCM case is defined from the mean forcings of the 3D model. This improves the signal-to-noise ratio, which enables a better judgement of the quality of boundary-layer parametrizations in a comparison with the observations
Original languageEnglish
Pages (from-to)671-684
JournalQuarterly Journal of the Royal Meteorological Society
Volume136
Issue number648
DOIs
Publication statusPublished - 2010

Keywords

  • atmospheric boundary-layer
  • simulation models
  • evaluation
  • meteorological observations
  • air flow
  • turbulence
  • stably stratified conditions
  • wind-structure variations
  • energy closure-model
  • land-surface
  • diurnal cycle
  • soil-moisture
  • stratocumulus
  • flux
  • cabauw

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