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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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Filip Lefebre Xavier Fettweis Hubert Gallée Jean-Pascal Van Ypersele Philippe Marbaix Wouter Greuell Pierluigi Calanca 《Climate Dynamics》2005,25(1):99-116
A simulation of the 1991 summer has been performed over south Greenland with a coupled atmosphere–snow regional climate model
(RCM) forced by the ECMWF re-analysis. The simulation is evaluated with in-situ coastal and ice-sheet atmospheric and glaciological
observations. Modelled air temperature, specific humidity, wind speed and radiative fluxes are in good agreement with the
available observations, although uncertainties in the radiative transfer scheme need further investigation to improve the
model’s performance. In the sub-surface snow-ice model, surface albedo is calculated from the simulated snow grain shape and
size, snow depth, meltwater accumulation, cloudiness and ice albedo. The use of snow metamorphism processes allows a realistic
modelling of the temporal variations in the surface albedo during both melting periods and accumulation events. Concerning
the surface albedo, the main finding is that an accurate albedo simulation during the melting season strongly depends on a
proper initialization of the surface conditions which mainly result from winter accumulation processes. Furthermore, in a
sensitivity experiment with a constant 0.8 albedo over the whole ice sheet, the average amount of melt decreased by more than
60%, which highlights the importance of a correctly simulated surface albedo. The use of this coupled atmosphere–snow RCM
offers new perspectives in the study of the Greenland surface mass balance due to the represented feedback between the surface
climate and the surface albedo, which is the most sensitive parameter in energy-balance-based ablation calculations. 相似文献
3.
Comte Valentin Schneider Léonard Calanca Pierluigi Rebetez Martine 《Theoretical and Applied Climatology》2022,147(1-2):423-436
Theoretical and Applied Climatology - In this study, we investigated the consequences of climate change on bioclimatic indices in vineyards along the edge of Lake Neuchatel in Switzerland. Like in... 相似文献
4.
Boundary layer characteristics and turbulent exchange mechanisms in highly complex terrain 总被引:2,自引:0,他引:2
Mathias W. Rotach Marco Andretta Pierluigi Calanca Andreas P. Weigel Alexandra Weiss 《Acta Geophysica》2008,56(1):194-219
The Mesoscale Alpine Programme’s Riviera project investigated the turbulence structure and related exchange processes in an
Alpine valley by combining a detailed experimental campaign with high-resolution numerical modelling. The present contribution
reviews published material on the Riviera Valley’s boundary layer structure and discusses new material on the near-surface
turbulence structure. The general conclusion of the project is that despite the large spatial variability of turbulence characteristics
and the crucial influence of topography at all scales, the physical processes can accurately be understood and modelled. Nevertheless,
many of the “text book characteristics” like the interaction between the valley and slope wind systems or the erosion of the
nocturnal valley inversion need reconsideration, at least for small non-ideal valleys like the Riviera Valley. The project
has identified new areas of research such as post-processing methods for turbulence variables in complex terrain and new approaches
for the surface energy balance when advection is non-negligible. The exchange of moisture and heat between the valley atmosphere
and the free troposphere is dominated by local “secondary” circulations due to the curvature of the valley axis. Because many
curved valleys exist, and operational models still have rather poor resolution, parameterization of these processes may be
required. 相似文献
5.
Changes of the summer evapotranspiration regime under increased levels of atmospheric greenhouse gases are discussed for three Alpine river basins on the basis of a new set of simulations carried out with a high-resolution hydrological model. The climate change signal was inferred from the output of two simulations with a state-of-the-art global climate model (GCM), a reference run valid for 1961–1990 and a time-slice simulation valid for 2071–2100 under forcing from the A2 IPCC emission scenario. In this particular GCM experiment and with respect to the Alpine region summer temperature was found to increase by 3 to 4 ∘C, whereas precipitation was found to decrease by 10 to 20%. Global radiation and water vapor pressure deficit were found to increase by about 5% and 2 hPa, respectively. On this background, an overall increase of potential evapotranspiration of about 20% relative to the baseline was predicted by the hydrological model, with important variations between but also within individual basins. The results of the hydrological simulations also revealed a reduction in the evapotranspiration efficiency that depends on altitude. Accordingly, actual evapotranspiration was found to increase at high altitudes and to the south of the Alps, but to decrease in low elevation areas of the northern forelands and in the inner-Alpine domain. Such a differentiation does not appear in the GCM scenario, which predicts an overall increase in evapotranspiration over the Alps. This underlines the importance of detailed simulations for the quantitative assessment of the regional impact of climate change on the hydrological cycle. 相似文献
6.
We present the integration of early 21st century climate projections for Europe based on simulations carried out within the EU-FP6 ENSEMBLES project with the LARS-WG stochastic weather generator. The aim was to upgrade ELPIS, a repository of local-scale climate scenarios for use in impact studies and risk assessments that already included global projections from the CMIP3 ensemble and regional scenarios for Japan. To obtain a more reliable simulation of daily rainfall and extremes, changes in wet and dry series derived from daily ENSEMBLES outputs were taken into account. Kernel average smoothers were used to reduce noise arising from sampling artefacts. Examples of risk analyses based on 25-km climate projections from the ENSEMBLES ensemble of regional climate models illustrate the possibilities offered by the updated version of ELPIS. The results stress the importance of tailored information for local-scale impact assessments at the European level. 相似文献
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