On the Anomalous Behaviour of Scalar Flux–Variance Similarity Functions Within the Canopy Sub-layer of a Dense Alpine Forest

Abstract

Within the canopy sub-layer (CSL), variability in scalar sources and sinks are known to affect flux-variance (FV) similarity relationships for water vapour (q) and carbon dioxide (C) concentrations, yet large-scale processes may continue to play a significant role. High frequency time series data for temperature (T ), q and C, collected within the CSL of an uneven-aged mixed coniferous forest in Lavarone, Italy, are used to investigate these processes within the context of FV similarity. This dataset suggests that MOST scaling describes the FV similarity function of T even though the observations are collected in the CSL, consistent with other studies. However, the measured FV similarity functions for q and C appear to have higher values than their temperature counterpart. Two hypotheses are proposed to explain the measured anomalous behaviour in the FV similarity functions for q and C when referenced to T . Respired CO 2 from the forest floor leads to large positive excursions in the C time series at the canopy top thereby contributing significantly to both C variance increase and C vertical flux decrease-both leading to an anomalous increase in the FV similarity function. For q, transport of dry air from the outer-layer significantly increases both the variance and the water vapour flux. However, the expected flux increase is much smaller than the variance increase so that the net effect remains an increase in the measured FV similarity function for water vapour above its T counterpart. The hypothesis here is that identifying these events in the temporal and/or in the frequency domain and filtering them from the C and q time series partially recovers a scalar flow field that appears to follow FV similarity theory scaling. Methods for identifying both types of events in the time and frequency domains and their subsequent effects on the FV similarity functions and corollary flow variables, such as the relative transport efficiencies, are also explored.

Scalar turbulent behavior in the roughness sublayer of an Amazonian forest

“…We obtained high correlations (in fact, higher than those reported by Cava et al, 2008). As these authors comment, these fluxes are calculated without knowledge of u * , and the success of the method under these more unstable conditions gives independent confirmation that spurious correlation is not contaminating our analyses.…”

“…This tendency of φ a data in the roughness sublayer to lie above the corresponding MOST functions is generally observed in field experiments (Cava et al, 2008;Dias et al, 2009), but a definitive explanation for it is still lacking.…”

Scaling Properties of Biologically Active Scalar Concentration Fluctuations in the Atmospheric Surface Layer over a Managed Peatland

“…Rather, it is revealed by the fact that the majority of points are well grouped around the model (better for temperature than for water vapour), with less scatter than expected if all variables were independent. This problem was recently explored by Cava et al (2008) using Table 1). Vertical grey lines indicate skewness or kurtosis values for a Gaussian distribution a randomization technique, and who concluded that, in both the near-neutral and convective regimes, the correlations were not mere statistical artefacts.…”

Scaling laws of turbulence intermittency in the atmospheric boundary layer: the role of stability

“…Dissimilarity of turbulent transport of momentum and scalars and the relations with the topology and the role of turbulent coherent structures as sweep and ejections is also investigated ( [11], [10], [12]) for different stability conditions. The sequence of intermittent bursting events is mainly described by two statistical indicators: the Inter-Event Times (IETs) distribution and the correlation among evens and IETs.…”