Monin-Obukhov Similarity Functions for the Structure Parameters of Temperature and Humidity

Dan Li, Elie R. Bou-Zeid, Henk A.R. de Bruin

Research output: Contribution to journalArticle

48 Scopus citations

Abstract

Monin-Obukhov similarity functions for the structure parameters of temperature and humidity are needed to derive surface heat and water vapour fluxes from scintillometer measurements and it is often assumed that the two functions are identical in the atmospheric surface layer. Nevertheless, this assumption has not yet been verified experimentally. This study investigates the dissimilarity between the turbulent transport of sensible heat and water vapour, with a specific focus on the difference between the Monin-Obukhov similarity functions for the structure parameters. Using two datasets collected over homogeneous surfaces where the surface sources of sensible heat and water vapour are well correlated, we observe that under stable and very unstable conditions, the two functions are similar. This similarity however breaks down under weakly unstable conditions; in that regime, the absolute values of the correlations between temperature and humidity are also observed to be low, most likely due to large-scale eddies that transport unsteadiness, advection or entrainment effects from the outer layer. We analyze and demonstrate how this reduction in the correlation leads to dissimilarity between the turbulent transport of these two scalars and the corresponding Monin-Obukhov similarity functions for their structure parameters. A model to derive sensible and latent heat fluxes from structure parameters without measuring the friction velocity is tested and found to work very well under moderately to strongly unstable conditions (-z/L > 0. 5). Finally, we discuss the modelling of the cross-structure parameter over wet surfaces, which is crucial for correcting water vapour effects on optical scintillometer measurements and also for obtaining surface sensible and latent heat fluxes from the two-wavelength scintillometry.

Original languageEnglish (US)
Pages (from-to)45-67
Number of pages23
JournalBoundary-Layer Meteorology
Volume145
Issue number1
DOIs
StatePublished - Sep 1 2012

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Keywords

  • Evaporation
  • Monin-Obukhov similarity
  • Scintillometry
  • Structure parameters
  • Temperature-humidity similarity

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