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A Lagrangian stochastic (LS) model, which is embedded into a parallelised large-eddy simulation (LES) model, is used for dispersion
and footprint evaluations. For the first time an online coupling between LES and LS models is applied. The new model reproduces
concentration patterns, which were obtained in prior studies, provided that subgrid-scale turbulence is included in the LS
model. Comparisons with prior studies show that the model evaluates footprints successfully. Streamwise dispersion leads to
footprint maxima that are situated less far upstream than previously reported. Negative flux footprints are detected in the
convective boundary layer (CBL). The wide range of applicability of the model is shown by applying it under neutral and stable
stratification. It is pointed out that the turning of the wind direction with height leads to a considerable dependency of
source areas on height. First results of an application to a heterogeneously heated CBL are presented, which emphasize that
footprints are severely affected by the inhomogeneity. 相似文献
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Mathias Göckede Tiina Markkanen Charlotte B. Hasager Thomas Foken 《Boundary-Layer Meteorology》2006,118(3):635-655
Horizontal heterogeneity can significantly affect the flux data quality at monitoring sites in complex terrain. In heterogeneous conditions, the adoption of the eddy-covariance technique is contraindicated by the lack of horizontal homogeneity and presence of advective conditions. In addition, uncertainty concerning the sources or sinks influencing a measurement compromises the data interpretation. The consideration of the spatial context of a measurement, defined by a footprint analysis, can therefore provide an important tool for data quality assessment. This study presents an update of an existing footprint-based quality evaluation concept for flux measurement sites in complex terrain. The most significant modifications in the present version are the use of a forward Lagrangian stochastic trajectory model for the determination of the spatial context of the measurements, and the determination of effective roughness lengths with a flux aggregation model in a pre-processing step. Detailed terrain data gathered by remote sensing methods are included. This approach determines spatial structures in the quality of flux data for varying meteorological conditions. The results help to identify terrain influences affecting the quality of flux data, such as dominating obstacles upwind of the site, or slopes biasing the wind field, so that the most suitable footprint regions for the collection of high-quality datasets can be identified. Additionally, the approach can be used to evaluate the performance of a coordinate rotation procedure, and to check to what extent the measured fluxes are representative for a target land-use type. 相似文献
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A method of moving precipitation totals is described and applied for the analysis of precipitation extremes in Estonia. Numbers of extremely wet and extremely dry days and other indices of precipitation extremes were calculated using the daily precipitation data measured at 51 stations over Estonia during 1957–2009. Mean regularities of spatial and seasonal distribution were determined. Long-term changes were detected using Sen's method and Mann–Kendall test. The highest risk of heavy precipitation is in the regions of higher mean precipitation on the uplands and on the belt of higher precipitation in the western part of continental Estonia. Wet spells have their sharp maxima in July and August. The highest risk of droughts is observed in the coastal regions of West Estonia. In the coastal area, droughts appear mostly in the first half of summer, while in the eastern Estonia, they are usually observed during the second half of summer. Extreme precipitation events have become more frequent and intense. Statistically significant increasing trends were, first of all, found in the time series of winter extreme precipitation indices. In summer and autumn, trends existed in some indices, but in spring, there were no trends at all. There were no trends in time series of dryness indices in Estonia in 1957–2009. 相似文献
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Knowledge of oil-induced impacts from the literature and experts were used to develop a Bayesian network to evaluate the biological consequences of an oil accident in the low-saline Gulf of Finland (GOF). Analysis was carried out for selected groups of organisms. Subnetworks were divided into subgroups according to a predicted response to oil exposure. Two scenario analyses are presented: the most probable and the worst-case accident.The impact of the most probable accident in the GOF is rather small. In most of the groups studied oil-induced long-term effects are evaluated to be minor at least from the perspective of the whole GOF. After the worst-case accident negative effects are more likely. The model predicts that the most vulnerable groups are auks and ducks. Amphipods, gulls and to a lesser extend littoral fishes and seals may show delayed recovery after an accident. Also annual plant species may be susceptible to oil-induced disturbances. 相似文献
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Footprints and Fetches for Fluxes over Forest Canopies with Varying Structure and Density 总被引:1,自引:1,他引:1
Tiina Markkanen Üllar Rannik Barbara Marcolla Alessandro Cescatti Timo Vesala 《Boundary-Layer Meteorology》2003,106(3):437-459
A stochastic trajectory model was used to estimate scalar fluxfootprints in neutral stabilityfor canopies of varying leaf area distributions andleaf area indices. An analytical second-order closure model wasused to predict mean wind speed, second moments and the dissipationrate of turbulent kinetic energy within a forest canopy.The influence of source vertical profile on the flux footprint wasexamined. The fetch is longer for surface sourcesthan for sources at higher levels in the canopy. In order tomeasure all the flux components, and thus the total flux, with adesired accuracy, sources were located at the forest floor in thefootprint function estimation. The footprint functions werecalculated for five observation levels above the canopy top. Itwas found that at low observation heights both canopy density andcanopy structure affect the fetch. The higher abovethe canopy top the flux is measured, the more pronounced is the effectof the canopy structure. The forest fetch for flux measurements isstrongly dependent on the required accuracy: The 90% flux fetchis greater by a factor of two or more compared to the 75% fetch. Theupwind distance contributing 75% of flux is as large as 45 timesthe difference between canopy height and the observation heightabove the canopy top, being even larger for low observationlevels. 相似文献
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Peeter Nõges Lea Tuvikene Tiina Nõges Anu Kisand 《Aquatic Sciences - Research Across Boundaries》1999,61(2):168-182
10.
Kelsey M. Lowe James Shulmeister Joshua M. Feinberg Tiina Manne Lynley A. Wallis Kevin Welsh 《Geoarchaeology》2016,31(3):211-228
In regions that lack built structures or stratified open archaeological sites, such as precolonial Australia, rockshelters are a major source of detailed information for understanding the nature and timing of human occupation. A key concern is that the proposed ages for the earliest archaeological sites are based on luminescence dating of sediments, rather than directly of cultural materials, leaving the association between the sediments and evidence of human activity questionable. Here, we present evidence of magnetic enhancement associated with cultural horizons within the deposits of a Pleistocene rockshelter in interior northern Queensland. Soil magnetic studies combined with experimental burning show that magnetically enhanced sediments in Gledswood Shelter 1 are the result of anthropogenic burning of hearth fires, which burn hotter and for a longer time than natural wild fires. These techniques appear to work in this setting because of the nature of the local geology and the geological antiquity of the landscape. Susceptibility and frequency dependence of susceptibility signatures provide a critical tool to resolve that human occupation starts at 2.2 m depth within a stratigraphic section. In conjunction with luminescence dating, soil magnetic studies provide an opportunity for archaeologists to resolve the timing of human settlement in Australia and other intracratonic plate settings. 相似文献