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

• Published in: Boundary - layer meteorology Vol. 145; no. 1; pp. 45 - 67
• Main Authors: Li, Dan, Bou-Zeid, Elie, De Bruin, Henk A. R.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Dordrecht Springer Netherlands 01-10-2012; Springer; Springer Nature B.V
• Subjects: Analysis; Atmospheric boundary layer; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Careers; Convection, turbulence, diffusion. Boundary layer structure and dynamics; Correlation; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Eddies; Exact sciences and technology; External geophysics; Fluxes; Humidity; Latent heat; Marine; Mathematical models; Meteorology; Sensible heat; Similarity; Temperature; Transport; Vapour; Water vapor; Monin–Obukhov similarity; Scintillometry; Structure parameters; Evaporation; Temperature–humidity similarity; advection; sensible heat; Friction velocity; models; Entrainment (atmosphere, ocean); Temperature-humidity similarity; Turbulent transport; Homogeneous surface; surface water; water vapor; Monin-Obukhov similarity; Atmospheric boundary layer; Scintillation counter; Vortex; evaporation; heat transfer; latent heat
• ISSN: 0006-8314; 1573-1472
• DOI: 10.1007/s10546-011-9660-y

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.