Sn Organotin Compounds

Schumann, Herbert; Schumann, Ingeborg; Krüerke, Ulrich

doi:10.1007/978-3-662-06612-6

Cited by 4 publications

(12 citation statements)

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“…In this paper it is shown that the Schumann (1988) model from one side, and the Sykes et al (1993) and Zilitinkevich et al (1998) models from the other side, are valid in certain intervals of h/z 0u . In the former model, the turbulent eddies are assumed to be determined by buoyant convection, even very close to the surface; in the latter models, the shear-driven turbulence is considered to be the only dominant factor close to the surface (this is not valid in the case of very high-roughness elements).…”

Section: Introductionmentioning

confidence: 74%

“…(a) Internal boundary layer: basic features and vertical profiles Following earlier models of Schumann (1988), Sykes et al (1993) and Zilitinkevich et al (1998), we assume that large eddies are characterized by the length-scale, h, and the velocity-scale, W * (see Eq. (1)), and live much longer than the CBL overturning time, h/W * ∼ 10 3 s (although shorter than the time-scale of the evolution of the mean flow).…”

Section: Large-eddy Boundary-layer Modelmentioning

confidence: 99%

“…Schumann (1988) derived the same equations but did not distinguish between z 0u and z 0 . He also obtained empirical estimates of C U 3 and C 3 from the LES of Schmidt and Schumann (1989).…”

Section: Large-eddy Boundary-layer Modelmentioning

confidence: 99%

“…Traditional local theories overlook this mechanism and underestimate the surface fluxes in strong convection. The eddy-shear models developed by Schumann (1988) and Sykes et al (1993) suggested how to combine the effects of the convectively generated turbulence, the shear generated turbulence and roughness effects at the surface. Schumann's model (a one-layer model assuming the dominant role of the buoyancy forces throughout the convergence flows) shows reasonably good correspondence with empirical data and data from large-eddy simulation (LES) of CBLs over moderately rough surfaces (10 4 < h/z 0u < 10 5 ), but becomes inaccurate in the asymptotic regimes of the low roughness (h/z 0u > 10 6 ) and the very high roughness (h/z 0u < 10 3 ).…”

Section: Introductionmentioning

confidence: 99%

“…In this context, L * is the depth over which the role of the shear processes becomes negligible. To validate their model, Zilitinkevich et al (1998) used field data, which gave essentially larger values of U * /W * than LES data used by Schumann (1988) and Sykes et al (1993). Akylas et al (2001Akylas et al ( , 2003 explained that this contradiction is due to the fact that empirical estimates of U * based on field data are practically always affected by the ambient mean wind.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

The influence of large convective eddies on the surface-layer turbulence

Zilitinkevich

Hunt

Esau

et al. 2006

Q. J. R. Meteorol. Soc.

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SUMMARYClose to the surface large coherent eddies consisting of plumes and downdraughts cause convergent winds blowing towards the plume axes, which in turn cause wind shears and generation of turbulence. This mechanism strongly enhances the convective heat/mass transfer at the surface and, in contrast to the classical formulation, implies an important role of the surface roughness. In this context we introduce the stability-dependence of the roughness length. The latter is important over very rough surfaces, when the height of the roughness elements becomes comparable with the large-eddy Monin-Obukhov length. A consistent theoretical model covering convective regimes over all types of natural surfaces, from the smooth still sea to the very rough city of Athens, is developed; it is also comprehensively validated against data from measurements at different sites and also through the convective boundary layer. Good correspondence between model results, field observations and large-eddy simulation is achieved over a wide range of surface roughness lengths and convective boundary-layer heights.

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Section: Introductionmentioning

confidence: 74%

Section: Large-eddy Boundary-layer Modelmentioning

confidence: 99%

Section: Large-eddy Boundary-layer Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

The influence of large convective eddies on the surface-layer turbulence

Zilitinkevich

Hunt

Esau

et al. 2006

Q. J. R. Meteorol. Soc.

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A physically based parametrization for surface flux enhancement by gustiness effects in dry and precipitating convection

Williams

2001

Quart J Royal Meteoro Soc

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SUMMARYEnhancement of bulk surface fluxes by subgrid variability is reviewed, with special attention to conditions ranging from fair-weather free convection to precipitating deep convection over uniform surfaces. Aircraft measurements in the Tropical OceanlGlobal Atmosphere Coupled Ocean-Atmosphere Response Experiment subcloud layer indicate that the predominant mechanism for flux enhancement is wind variability associated with both boundary-layer-scale coherent eddies (dry convective gustiness) and density currents beneath precipitating convection (moist convective gustiness). A new evaluation of the dry convective gustiness parameter, /?, supports recent indications that its effective value is less than previously thought (0.60-0.80, rather than 1 .OO-1.25), due both to a discrepancy in the technique often used for its estimation from field data, and to contamination of datasets by meso-y-scale (-10 km) motions. A strong relationship is found in the aircraft time series between the moist convective gustiness velocity and the theoretical speed of density-current gust fronts driven by the observed meso-y -scale temperature variability. This prompts development of a simple theoretical model for the latter, based upon a known convective rainfall rate and ambient thermodynamic structure for the lower atmosphere. Parameters in the model are estimated using data from simultaneous aircraft and shipboard radar measurements, and model behaviour is compared with a simpler scheme developed by MCtto-France. It is concluded that an explicit representation of the rain evaporation process in the generation of density perturbations is crucial for accurate determination of the strength of moist convective gustiness in the model, and through it the degree of surface flux enhancement.

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Considerations on minimum friction velocity

Akylas

Tsakos

Tombrou

et al. 2003

Quart J Royal Meteoro Soc

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SUMMARYThe concept of the minimum friction velocity is studied using three different methods of scalar averaging for the calculation of the stresses. Particular emphasis is given to the extraction of the in uence of a non-zero ambient wind shear observed in eld measurements. Data from three different experimental sites in Athens with high roughness values are analysed in order to provide information concerning the dependence of the dimensionless minimum friction velocity on the dimensionless roughness length. Data from the BOREX-95 experiment have also been re-analysed according to the methodologies presented in this study. The results are compared to the large-eddy simulations that are considered to be a reference study on shear-free convection.

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Sn Organotin Compounds

Cited by 4 publications

References 0 publications

The influence of large convective eddies on the surface-layer turbulence

The influence of large convective eddies on the surface-layer turbulence

A physically based parametrization for surface flux enhancement by gustiness effects in dry and precipitating convection

Considerations on minimum friction velocity

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