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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
3.
Boundary-Layer Meteorology - When wind blows over the ocean, short wind-waves (of wavelength smaller than 10 m) are generated, rapidly reaching an equilibrium with the overlying turbulence (at... 相似文献
4.
Interpreting CO<Subscript>2</Subscript> Fluxes Over a Suburban Lawn: The Influence of Traffic Emissions 总被引：1，自引：0，他引：1
Turf-grass lawns are ubiquitous in the United States. However direct measurements of land–atmosphere fluxes using the eddy-covariance
method above lawn ecosystems are challenging due to the typically small dimensions of lawns and the heterogeneity of land
use in an urbanised landscape. Given their typically small patch sizes, there is the potential that CO2 fluxes measured above turf-grass lawns may be influenced by nearby CO2 sources such as passing traffic. In this study, we report on two years of eddy-covariance flux measurements above a 1.5 ha
turf-grass lawn in which we assess the contribution of nearby traffic emissions to the measured CO2 flux. We use winter data when the vegetation was dormant to develop an empirical estimate of the traffic effect on the measured
CO2 fluxes, based on a parametrised version of a three-dimensional Lagrangian footprint model and continuous traffic count data.
The CO2 budget of the ecosystem was adjusted by 135gCm−2 in 2007 and by 134gCm−2 in 2008 to determine the natural flux, even though the road crossed the footprint only at its far edge. We show that bottom-up
flux estimates based on CO2 emission factors of the passing vehicles, combined with the crosswind-integrated footprint at the distance of the road, agreed
very well with the empirical estimate of the traffic contribution that we derived from the eddy-covariance measurements. The
approach we developed may be useful for other sites where investigators plan to make eddy-covariance measurements on small
patches within heterogeneous landscapes where there are significant contrasts in flux rates. However, we caution that the
modelling approach is empirical and will need to be adapted individually to each site. 相似文献
5.
Summary
The interaction of a cold front with the Alps is studied by means of real-case numerical simulations for a case occurring
at the end of the Alpine Experiment (ALPEX) on 28 April–2 May, 1982. Simulations are performed with the numerical weather
prediction model chain Europa-Modell (EM) and its one-way nested high-resolution model (HM) of the German and Swiss Weather
Services. The outer EM simulation (56 km horizontal resolution) uses initial and lateral boundary fields taken from the ALPEX-IIIb
reanalysis data set. This reanalysis data set is based on the operational EM analysis scheme, but takes into consideration
a wide range of field phase data taken during the ALPEX field campaign. A comparison of simulations driven by the ALPEX and
ECMWF reanalysis (ERA) data is performed. The simulation driven by the former captures the intensity and vertical depth of
the developing lee cyclone substantially better than the corresponding run driven by the ERA.
The transient development of the impingement of a cold front on the Alps induces a wide range of mesoscale phenomenon such
as flow splitting, mistral, north foehn, cyclogenesis, anticyclonic vortex and bora. These flow evolutions are analyzed using
HM simulations with a horizontal resolution of 14 km and visualized performing comprehensive trajectory calculations.
Received September 9, 2000/Revised November 28, 2000 相似文献
6.
A Three-Dimensional Backward Lagrangian Footprint Model For A Wide Range Of Boundary-Layer Stratifications 总被引：5，自引：3，他引：5
We present a three-dimensional Lagrangian footprint model with the ability to predict the area of influence (footprint) of a measurement within a wide range of boundary-layer stratifications and receptor heights. The model approach uses stochastic backward trajectories of particles and satisfies the well-mixed condition in inhomogeneous turbulence for continuous transitions from stable to convective stratification. We introduce a spin-up procedure of the model and a statistical treatment of particle touchdowns which leads to a significant reduction of CPU time compared to conventional footprint modelling approaches. A comparison with other footprint models (of the analytical and Lagrangian type) suggests that the present backward Lagrangian model provides valid footprint predictions under any stratification and, moreover, for applications that reach across different similarity scaling domains (e.g., surface layer to mixed layer, for use in connection with aircraft measurements or with observations on high towers). 相似文献
7.
T. J. Griffis J. Zhang J. M. Baker N. Kljun K. Billmark 《Boundary-Layer Meteorology》2007,123(2):295-316
In recent years considerable effort has been focused on combining micrometeorological and stable isotope techniques to partition
net fluxes and to study biosphere–atmosphere exchange processes. While much progress has been achieved over the last decade,
some new issues are beginning to emerge as technological advances, such as laser spectroscopy, permit isotopic fluxes to be
measured more easily and continuously in the field. Traditional investigations have quantified the isotopic composition of
biosphere-atmosphere exchange by using the Keeling two-member mixing model (the classic Keeling plot). An alternative method,
based on a new capacity to measure isotopic mixing ratios, is to determine the isotope composition of biosphere–atmosphere
exchange from the ratio of flux measurements. The objective of this study was to critically evaluate these methods for quantifying
the isotopic composition of ecosystem respiration (δR) over a period of three growing seasons (2003–2005) within a heterogeneous landscape consisting of C3 and C4 species. For C4 canopies, the mixing model approach produced δR values that were 4–6‰ lower (isotopically lighter) than the flux-gradient method. The analyses presented here strongly suggest
that differences between flux and concentration footprint functions are the main factor influencing the inequality between
the mixing model and flux-gradient approaches. A mixing model approach, which is based on the concentration footprint, can
have a source area influence more than 20-fold greater than the flux footprint. These results highlight the fact that isotopic
flux partitioning is susceptible to problems arising from combining signals (concentration and fluxes) that represent very
different spatial scales (footprint). This problem is likely to be most pronounced within heterogeneous terrain. However,
even under ideal conditions, the mismatch between concentration and flux footprints could have a detrimental impact on isotopic
flux partitioning where very small differences in isotopic signals must be resolved. 相似文献
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