Structure Inclination Angles and Amplitude Modulation Behavior in the Atmospheric Surface Layer
| Buoyancy effects on coherent structures in the atmospheric surface layer are investigated using field data, with a focus on the mean inclination angle and amplitude modulation (AM) by large-scale motions as functions of the Monin-Obukhov stability parameter (𝑧/𝐿). Observational data from the rough-terrain CASES99 experiment show that mean inclination angles increase with thermal intensity, following the expected physical interplay between shear and buoyancy forces. An AM model is developed based on the angles of large- and small-scale structures, interpreting AM as the cosine of the phase between them. Preliminary analysis of laboratory data from a thermally neutral boundary layer flow examines how the model performs across an extended height range—particularly when the characteristic streamwise eddy wavelength is assumed to increase linearly with height, and the extent to which this is consistent with the attached eddy hypothesis. We further examine the model’s capability to capture the increasing AM trend with thermal intensity in near-surface heights. Finally, we investigate thermal effects on the inner-outer interaction model by Marusic (2010), as both AM and coherent structure features are embedded in the model parameters. |
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