Large Wind Farms and the Scalar Flux over an Heterogeneously Rough Land Surface   总被引：2，自引：2，他引：0  

Marc Calaf  Chad Higgins  Marc B. Parlange 《Boundary-Layer Meteorology》2014,153(3):471-495

The influence of surface heterogeneities extends vertically within the atmospheric surface layer to the so-called blending height, causing changes in the fluxes of momentum and scalars. Inside this region the turbulence structure cannot be treated as horizontally homogeneous; it is highly dependent on the local surface roughness, the buoyancy and the horizontal scale of heterogeneity. The present study analyzes the change in scalar flux induced by the presence of a large wind farm installed across a heterogeneously rough surface. The change in the internal atmospheric boundary-layer structure due to the large wind farm is decomposed and the change in the overall surface scalar flux is assessed. The equilibrium length scale characteristic of surface roughness transitions is found to be determined by the relative position of the smooth-to-rough transition and the wind turbines. It is shown that the change induced by large wind farms on the scalar flux is of the same order of magnitude as the adjustment they naturally undergo due to surface patchiness.  相似文献   

Flow over Hills: A Large-Eddy Simulation of the Bolund Case   总被引：6，自引：6，他引：0  

Marc Diebold  Chad Higgins  Jiannong Fang  Andreas Bechmann  Marc B. Parlange 《Boundary-Layer Meteorology》2013,148(1):177-194

Simulation of local atmospheric flows around complex topography is important for several applications in wind energy (short-term wind forecasting and turbine siting and control), local weather prediction in mountainous regions and avalanche risk assessment. However, atmospheric simulation around steep mountain topography remains challenging, and a number of different approaches are used to represent such topography in numerical models. The immersed boundary method (IBM) is particularly well-suited for efficient and numerically stable simulation of flow around steep terrain. It uses a homogenous grid and permits a fast meshing of the topography. Here, we use the IBM in conjunction with a large-eddy simulation (LES) and test it against two unique datasets. In the first comparison, the LES is used to reproduce experimental results from a wind-tunnel study of a smooth three-dimensional hill. In the second comparison, we simulate the wind field around the Bolund Hill, Denmark, and make direct comparisons with field measurements. Both cases show good agreement between the simulation results and the experimental data, with the largest disagreement observed near the surface. The source of error is investigated by performing additional simulations with a variety of spatial resolutions and surface roughness properties.  相似文献   

Towards a Method for Quantitative LA‐ICP‐MS Imaging of Multi‐Phase Assemblages: Mineral Identification and Analysis Correction Procedures     

Bence Paul  Jon D. Woodhead  Chad Paton  Janet M. Hergt  John Hellstrom  C. Ashley Norris 《Geostandards and Geoanalytical Research》2014,38(3):253-263

Here, we present an approach to laser ablation ICP‐MS mapping of multi‐phase assemblages that permits the use of different internal standard elements, concentration values and reference materials for each mineral. In this way, we obtain not only broad pictures of elemental distributions within samples but can also extract high accuracy concentration data for any user‐selected region. This is accomplished by assigning regions of an image to corresponding mineral phases on a pixel‐by‐pixel basis. In this way, accurate trace element concentrations can be determined for each mineral phase, despite potential variations in their ablation characteristics. We present an example where elemental maps are constructed from ablation of a gabbroic sample that includes the phases apatite, amphibole and plagioclase. This work represents an important first step towards development of a method to produce highly accurate LA‐ICP‐MS elemental maps of multi‐phase samples.  相似文献   

Characterizing snowmelt anomalies in hydrochemographs of a karst spring,Cumberland Valley,Pennsylvania (USA): evidence for multiple recharge pathways   总被引：1，自引：1，他引：0  

Chad E. Reisch  Laura Toran 《Environmental Earth Sciences》2014,72(1):47-58

Conductivity, water level, air temperature, and depth of snowpack were monitored during a 26-day melt period of 88-cm-deep snowpack at a karst spring to characterize internal runoff and diffuse infiltration. Chloride from road salt provided a tracer and the snowpack a recharge source during the melt period. The melt period was divided into phases based on air temperature and chemograph pattern. For the first and third phases, mean air temperatures were below freezing, but above freezing during the second and fourth phases. During the first phase when the temperature peaked above freezing, conductivity typically spiked 10–50 μS/cm, suggesting input of road salt from conduits. When the snowpack continuously melted, conductivity and water-level trends were upward with smaller daily spikes in conductivity indicating infiltration from the dilute snowpack. This pattern suggests that road salt input continued when snowmelt recharged through the epikarst, but at lower concentrations than the conduit input. Refreezing of the snowpack and shallow subsurface for a brief period interrupted the recharge, and there was no longer a sawtooth pattern of conductivity. It is apparent that frozen conditions did not cease recharge because a dual recharge process was evident. While dual recharge from internal runoff and diffuse infiltration occurred, the portions varied because of changing melting rates. Observed patterns indicated internal runoff dominated during frozen periods because recharge water moved as overland flow across a frozen surface to focused pathways. Diffuse infiltration became available during warmer periods because subsurface thawing allowed the snowmelt to penetrate the epikarst. Results of snowmelt monitoring in spring discharge indicated the transient nature of karst recharge.  相似文献   

Comparison of bulk and compound-specific δC analyses and determination of carbon sources to salt marsh sediments using n-alkane distributions (Maine,USA)     

Benjamin R. Tanner  Maria E. Uhle  Claudia I. Mora  Joseph T. Kelley  Patrick J. Schuneman  Chad S. Lane  Evan S. Allen 《Estuarine, Coastal and Shelf Science》2010

Sources of sedimentary organic matter to a Morse River, Maine (USA) salt marsh over the last 3390 ± 60 RCYBP (Radiocarbon Years Before Present) are determined using distribution patterns of n-alkanes, bulk carbon isotopic analysis, and compound-specific carbon isotopic analysis. Marsh foraminiferal counts suggest a ubiquitous presence of high marsh and higher-high marsh deposits (dominated by Trochammina macrescens forma macrescens, Trochammina comprimata, and Trochammina inflata), implying deposition from ∼0.2 m to 0.5 m above mean high water. Distributions of n-alkanes show a primary contribution from higher plants, confirmed by an average chain length value of 27.5 for the core sediments, and carbon preference index values all >3. Many sample depths are dominated by the C₂₅ alkane. Salicornia depressa and Ruppia maritima have similar n-alkane distributions to many of the salt marsh sediments, and we suggest that one or both of these plants is either an important source to the biomass of the marsh through time, or that another unidentified higher plant source is contributing heavily to the sediment pool. Bacterial degradation or algal inputs to the marsh sediments appear to be minor. Compound-specific carbon isotopic analyses of the C₂₇ alkane are on average 7.2‰ depleted relative to bulk values, but the two records are strongly correlated (R² = 0.89), suggesting that marsh plants dominate the bulk carbon isotopic signal. Our study underscores the importance of using caution when applying mixing models of plant species to salt marsh sediments, especially when relatively few plants are included in the model.  相似文献