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1.
We compare flux and concentration footprint estimates of athree-dimensional Lagrangian stochastic dispersion modelapplying backward trajectories with the results of ananalytical footprint model by Kormann and Meixner.The comparison is performed for varying stability regimesof the surface layer as well as for different measurementheights. In general, excellent correspondence is found. 相似文献
2.
A Simple Parameterisation for Flux Footprint Predictions 总被引：9，自引：6，他引：9
Flux footprint functions estimate the location and relative importance of passive scalar sources influencing flux measurements
at a given receptor height. These footprint estimates strongly vary in size, depending on receptor height, atmospheric stability,
and surface roughness. Reliable footprint calculations from, e.g., Lagrangian stochastic models or large-eddy simulations
are computationally expensive and cannot readily be computed for long-term observational programs. To facilitate more accessible
footprint estimates, a scaling procedure is introduced for flux footprint functions over a range of stratifications from convective
to stable, and receptor heights ranging from near the surface to the middle of the boundary layer. It is shown that, when
applying this scaling procedure, footprint estimates collapse to an ensemble of similar curves. A simple parameterisation
for the scaled footprint estimates is presented. This parameterisation accounts for the influence of the roughness length
on the footprint and allows for a quick but precise algebraic footprint estimation. 相似文献
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M. W. Rotach 《Boundary-Layer Meteorology》1993,65(1-2):1-28
5.
Refraction effects of optical beams are generally caused by an inhomogeneous propagation medium and are a major source of systematic errors in the precise optical determination of angles and distances in the atmospheric surface layer. In this contribution a method for deriving vertical temperature and refractive index gradients from optical scintillation is presented. Knowledge of these gradients is required for the compensation of atmospherically induced errors for highly precise terrestrial geodetic measurements, like direct transfer and levelling. The advantage of the present optical method is, that temperature and refractive index gradients can be derived as line-averaged values over the propagation path, which is not possible by meteorological point measurements. Field observations have been carried out with a displaced-beam scintillometer over flat terrain and under different atmospheric conditions in order to verify this method. The experiments show, that this method allows to derive accurate correction values for precise terrestrial geodetic measurements. 相似文献
6.
The effect of mountainous topography on moisture exchange between the “surface” and the free atmosphere 总被引：1，自引：0，他引：1
Typical numerical weather and climate prediction models apply parameterizations to describe the subgrid-scale exchange of
moisture, heat and momentum between the surface and the free atmosphere. To a large degree, the underlying assumptions are
based on empirical knowledge obtained from measurements in the atmospheric boundary layer over flat and homogeneous topography.
It is, however, still unclear what happens if the topography is complex and steep. Not only is the applicability of classical
turbulence schemes questionable in principle over such terrain, but mountains additionally induce vertical fluxes on the meso-γ
scale. Examples are thermally or mechanically driven valley winds, which are neither resolved nor parameterized by climate
models but nevertheless contribute to vertical exchange. Attempts to quantify these processes and to evaluate their impact
on climate simulations have so far been scarce. Here, results from a case study in the Riviera Valley in southern Switzerland
are presented. In previous work, measurements from the MAP-Riviera field campaign have been used to evaluate and configure
a high-resolution large-eddy simulation code (ARPS). This model is here applied with a horizontal grid spacing of 350 m to
detect and quantify the relevant exchange processes between the valley atmosphere (i.e. the ground “surface” in a coarse model)
and the free atmosphere aloft. As an example, vertical export of moisture is evaluated for three fair-weather summer days.
The simulations show that moisture exchange with the free atmosphere is indeed no longer governed by turbulent motions alone.
Other mechanisms become important, such as mass export due to topographic narrowing or the interaction of thermally driven
cross-valley circulations. Under certain atmospheric conditions, these topographical-related mechanisms exceed the “classical”
turbulent contributions a coarse model would see by several times. The study shows that conventional subgrid-scale parameterizations
can indeed be far off from reality if applied over complex topography, and that large-eddy simulations could provide a helpful
tool for their improvement. 相似文献
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Eleni Sfyri Mathias W. Rotach Ivana Stiperski Fred C. Bosveld Manuela Lehner Friedrich Obleitner 《Boundary-Layer Meteorology》2018,169(1):11-46
The scaled standard deviations of temperature and humidity are investigated in complex terrain. The study area is a steep Alpine valley, with six measurement sites of different slope, orientation and roughness (i-Box experimental site, Inn Valley, Austria). Examined here are several assumptions forming the basis of Monin–Obukhov similarity theory (MOST), including constant turbulence fluxes with height and the degree of self-correlation between the involved turbulence variables. Since the basic assumptions for the applicability of the MOST approach—horizontally homogeneous and flat conditions—are violated, the analysis is performed based on a local similarity hypothesis. The scaled standard deviations as a function of local stability are compared with previous studies from horizontally homogeneous and flat terrain, horizontally inhomogeneous and flat terrain, weakly inhomogeneous and flat terrain, as well as complex terrain. As a reference, similarity relations for unstable and stable conditions are evaluated using turbulence data from the weakly inhomogeneous and flat terrain of the Cabauw experimental site in the Netherlands, and assessed with the same post-processing method as the i-Box data. Significant differences from the reference curve and also among the i-Box sites are noted, especially for data derived from the i-Box sites with steep slopes. These differences concern the slope and the magnitude of the best-fit curves, illustrating the site dependence of any similarity theory. 相似文献
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M. W. Rotach 《Boundary-Layer Meteorology》1993,66(1-2):75-92
10.
M. W. Rotach S.-E. Gryning E. Batchvarova A. Christen R. Vogt 《Meteorology and Atmospheric Physics》2004,87(1-3):39-56
Summary In this publication first results of an urban tracer experiment are reported. This experiment was realized in the framework of the Basel UrBan Boundary-Layer Experiment (BUBBLE) in an area with abundant information on turbulence and flow conditions available. Release height was close to roof level and so was the height of the concentration samplers. The meteorological conditions during the experiments were mainly convective, but due to the rough character of the underlying surface also the mechanical turbulence was substantial.The concentration distribution is found to be essentially Gaussian in the horizontal plane and some commonly used methods to estimate the plume widths in applied dispersion models are compared to the observations. From measurements at one site downwind of the source it is found that for a near-roof level source, only an insignificant vertical gradient in tracer concentration is present within a street canyon. Using a Lagrangian Particle Dispersion Model the tracer experiments are simulated. It is shown that the exact form of the parameterization for the flow and turbulence structure within the urban roughness sublayer is of great importance for the simulation results. Also the numerical simulation results underline the necessity (and difficulty) to describe the vertical profile of the dissipation rate of turbulent kinetic energy close to an urban surface. 相似文献