Structure Function Analysis of Two-Scale Scalar Ramps. Part II: Ramp Characteristics and Surface Renewal Flux Estimation

• Published in: Boundary - layer meteorology Vol. 145; no. 1; pp. 27 - 44
• Main Authors: Shapland, T. M., McElrone, A. J., Snyder, R. L., Paw U, K. T.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Dordrecht Springer Netherlands 01.10.2012; Springer; Springer Nature B.V
• Subjects: Atmospheric boundary layer; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Canopies; Careers; Coherence; Convection, turbulence, diffusion. Boundary layer structure and dynamics; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Fluid dynamics; Function analysis; Grounds; Mass transport; Meteorology; Ramps; Scalars; Spectral analysis; Temperature; Transport processes; Turbulence; Wind shear; Structure functions; Flux-variance; Coherent structures; Turbulence; Temperature ramps; Surface renewal; Structure function; Energy transport; Surface layer; energy transfer; spectral analysis; turbulence; Variance; Intermittency; Transport process; Atmospheric boundary layer; Scalar field; calibration; Wind shear; Surface energy; Canopy(vegetation)
• ISSN: 0006-8314; 1573-1472
• DOI: 10.1007/s10546-012-9740-7

Ramp features in the turbulent scalar field are associated with turbulent coherent structures, which dominate energy and mass fluxes in the atmospheric surface layer. Although finer scale ramp-like shapes embedded within larger scale ramp-like shapes can readily be perceived in turbulent scalar traces, their presence has largely been overlooked in the literature. We demonstrate the signature of more than one ramp scale in structure functions of the turbulent scalar field measured from above bare ground and two types of short plant canopies, using structure-function time lags ranging in scale from isotropic to larger than the characteristic coherent structures. Spectral analysis of structure functions was used to characterize different scales of turbulent structures. By expanding structure function analysis to include two ramp scales, we characterized the intermittency, duration, and surface renewal flux contribution of the smallest (i.e., Scale One) and the dominant (i.e., Scale Two) coherent structure scales. The frequencies of the coherent structure scales increase with mean wind shear, implying that both Scale One and Scale Two are shear-driven. The embedded Scale One turbulent structure scale is ineffectual in the surface-layer energy and mass transport process. The new method reported here for obtaining surface renewal-based scalar exchange works well over bare ground and short canopies under unstable conditions, effectively eliminating the α calibration for these conditions and forming the foundation for analysis over taller and more complex surfaces.