International turbulence comparison experiment (ITCE-81)

588

328

This historical survey shows that Obukhov's 1946 fundamental paper on a universal length scale for exchange processes in the surface layer was the basis for the derivation of the similarity theory by Monin and Obukhov in 1954. A brief overview of the experiments and findings used to formulate the universal functions in the presently used form is given. Finally, the current status of the theory is described, covering topics such as the accuracy of the universal functions and the turbulent Prandtl number.

Section: Introductionmentioning

confidence: 99%

50 Years of the Monin–Obukhov Similarity Theory

Foken

2006

588

328

“…The first experiment was carried out in 1968 near Vancouver, Canada, over the ocean (Miyake et al 1971), followed by one over steppe country at Tsimlyansk, Russia in 1970 (Tsvang et al 1973). Additional experiments were carried out in 1976 in Conargo, Australia (Dyer 1981;Dyer et al 1982) and in 1981 again in Tsimlyansk (Tsvang et al 1985). In these early intercomparison experiments mostly prototype instrumentation was tested.…”

Section: Introductionmentioning

confidence: 99%

The energy balance experiment EBEX-2000. Part II: Intercomparison of eddy-covariance sensors and post-field data processing methods

Mauder

Oncley

Vogt

et al. 2006

197

166

The eddy-covariance method is the primary way of measuring turbulent fluxes directly. Many investigators have found that these flux measurements oftenThe National Center for Atmospheric Research is supported by the National Science Foundation. do not satisfy a fundamental criterion-closure of the surface energy balance. This study investigates to what extent the eddy-covariance measurement technology can be made responsible for this deficiency, in particular the effects of instrumentation or of the post-field data processing. Therefore, current eddy-covariance sensors and several post-field data processing methods were compared. The differences in methodology resulted in deviations of 10% for the sensible heat flux and of 15% for the latent heat flux for an averaging time of 30 min. These disparities were mostly due to different sensor separation corrections and a linear detrending of the data. The impact of different instrumentation on the resulting heat flux estimates was significantly higher. Large deviations from the reference system of up to 50% were found for some sensor combinations. However, very good measurement quality was found for a CSAT3 sonic together with a KH20 krypton hygrometer and also for a UW sonic together with a KH20. If these systems are well calibrated and maintained, an accuracy of better than 5% can be achieved for 30-min values of sensible and latent heat flux measurements. The results from the sonic anemometers Gill Solent-HS, ATI-K, Metek USA-1, and R.M. Young 81000 showed more or less larger deviations from the reference system. The LI-COR LI-7500 open-path H 2 O/CO 2 gas analyser in the test was one of the first serial numbers of this sensor type and had technical problems regarding direct solar radiation sensitivity and signal delay. These problems are known by the manufacturer and improvements of the sensor have since been made.

“…As to the magnitude of the exponent in (lo), a number of experimenters have pointed out that dimensional considerations suggest that +,, should become proportional to (-z/L)-"~ as conditions approach free convection (e.g., Carl et al, 1973;Troen and Mahrt, 1986). Measurements by Tsvang et al (1985) were shown to fit a -l/3 power relation over the range -0.70 < zlL < -0.03.…”

Section: Introductionmentioning

confidence: 99%

The turbulent kinetic energy budget in the atmospheric surface layer: A review and an experimental reexamination in the field

Frenzen¹,

Vogel²

1992

The one-dimensional equation for the turbulent kinetic energy budget in steady, horizontally-homogeneous flow near the ground is reviewed, and some of the many experimental evaluations of its stability-dependent terms obtained during the last twenty years are compared. Uncertainties attributable to instrument error and inadequate sites are discussed, and it is demonstrated that improved equipment makes it possible to evaluate contributions to the budget with comparatively simple experiments. A preliminary field study finds a von Karman constant of k = 0.387 + 0.016 and a wind shear function for the unstable surface layer 4,,, = (1 -22.6z/L)-I":the form (1 -15.lzlL))"' fits equally well over the limited range of instability observed. Turbulence dissipation is found to be 15 to 20% too small to balance the production of energy by wind shear in the neutral surface layer, and this deficit appears to remain approximately constant relative to the total rate of energy production as instability increases to z/L = -0.12. Renormalized dissipation rates originally measured by others are shown to exhibit similar behavior beyond this narrow range. Combining these results with those of the present study suggests a dissipation function of the form 4. = +,,, -z/L + c in which c = -0.16 represents a near constant, net negative contribution made by the sum of the divergent transport terms.