Monin–Obukhov Similarity Functions of the Structure Parameter of Temperature and Turbulent Kinetic Energy Dissipation Rate in the Stable Boundary Layer

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.

“…with independent flux measurements. More recent studies by Andreas and Hicks (2002) and Hartogensis and de Bruin (2005) deal with other MOST relationships.…”

Section: Discussionmentioning

confidence: 99%

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

Cava

Katul

Sempreviva

et al. 2008

“…The Hill (1981) correction (his Eq. 5) is derived for weak scattering and includes inner scale effects that, independent of saturation, are expected to occur when D/l o < 20 (Hill and Ochs 1978;Moene et al 2005;Hartogensis 2006). Considering that "strong weak" scattering occurs in our experiment, and that D = 0.15 m, inner scale effects are expected for l o even less than 7.5 mm.…”

Section: Saturation Theory and Correctionsmentioning

confidence: 66%

Test of Scintillometer Saturation Correction Methods Using Field Experimental Data

Kleissl

Hartogensis

Gómez-Díaz

2010

Self Cite

Saturation of large aperture scintillometer (LAS) signals can result in sensible heat flux measurements that are biased low. A field study with LASs of different aperture sizes and path lengths was performed to investigate the onset of, and corrections for, signal saturation. Saturation already occurs at C 2 n ≈ 0.074D 5/3 λ 1/3 L −8/3 , where C 2 n is the structure parameter of the refractive index, D is the aperture size, λ is the wavelength, L is the transect length, which is smaller than theoretically derived saturation limits. At a transect length of 1 km, a height of 2.5 m, and aperture ≈0.15 m the correction factor exceeds 5% already at C 2 n = 2 × 10 −12 m −2/3 , which will affect many practical applications of scintillometry. The Clifford correction method, which only depends on C 2 n and the transect geometry, provides good saturation corrections over the range of conditions observed in our study. The saturation correction proposed by Ochs and Hill results in correction factors that are too small in large saturation regimes. An inner length scale dependence of the saturation correction factor was not observed. Thus for practical applications the Clifford correction method should be applied.

“…The majority of other studies report higher values for this parameter. However, Hartogensis and De Bruin (2005) found even lower values of b 1 based on the CASES-99 experiment. They pointed out several possible reasons for lower values of φ ε in stable and very stable conditions, including: inaccuracies in the von Kármán and Kolmogorov constants, a short averaging period (they used 5-min time intervals to exclude non-turbulent contributions), and a limited number of data for very stable conditions in previous studies.…”

Section: The Spectra Of Velocity Componentsmentioning

confidence: 76%

“…Even if its relation with φ ε is not as straightforward as in the case of φ m , the non-linearity of φ ε for large ζ could be forced by self-correlation. However, Hartogensis and De Bruin (2005) proved that spurious correlation does not determine the shape of the φ ε function, but only affects the scatter of the data. The same was shown for φ m by Baas et al (2006).…”

Section: The Spectra Of Velocity Componentsmentioning

confidence: 99%

Selected Spectral Characteristics of Turbulence over an Urbanized Area in the Centre of Łódź, Poland

Fortuniak

Pawlak

2014

We present the turbulence spectra and cospectra derived from more than five years of eddy-covariance measurements at two urban sites in Łódź, central Poland. The fast response wind velocity components were obtained using sonic anemometers placed on narrow masts at 37 and 42 m above ground level. The analysis follows Kaimal et al. (Q J R Meteorol Soc 98:563-589, 1972) who established the spectral and cospectral properties of turbulent flow in atmospheric surface layer on the basis of the Kansas experiment. Our results illustrate many features similar to those of Kaimal et al., but some differences are also observed. The velocity (co)spectra from Łódź show a clear inertial subrange with −2/3 slope for spectra and −4/3 slope for cospectra. We found that an appropriate stability function for the non-dimensional dissipation of turbulent kinetic energy calculated from spectra in the inertial subrange differs from that of Kaimal et al., and it can be satisfactorily estimated with the assumption of local equilibrium using standard functions for the non-dimensional shear production. A similar function for the cospectrum corresponds well to Kaimal et al. for unstable and weakly stable conditions. The (co)spectra normalized by their spectral values in the inertial subrange are in general similar to those of Kaimal et al., but they peak at lower frequencies in strongly stable conditions. Moreover, our results do not confirm the existence of a clear "excluded region" at low frequencies for the transition from stable to unstable conditions, for longitudinal and lateral wind components. The empirical models of Kaimal et al. with adjusted parameters fit well to the vertical velocity spectrum and the vertical momentum flux cospectrum. The same type of function should be used for longitudinal and lateral wind spectra because of their sharper peak than occurs for the Kansas data. Finally, it should be stressed that the above relationships are well-defined for averaged values. The results for individual 1-h periods are very scattered and can be significantly different from the generalized functions.