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1.
A regional atmospheric climate model is used toexamine the effect of changes in the roughnesslengths of momentum (z0m) and heat (z0h)on the structure of the lower atmosphere and on thesurface energy fluxes over Antarctica. Fourexperiments were carried out in which z0mand/or z0h were altered with respect to acontrol experiment. The changes consisted of (1) alowering of z0m from a field aggregated froma vegetation map with an orographic correction basedon the European Centre for Medium-Range WeatherForecasts z0m field, to a constant value of10-3 m; and (2) a lowering of z0h from a valueequal to z0m to a constant value of 10-3 mor a value dependent on the wind speed via a surfacerenewal model. A reduction of z0m results in theexpected increase in near-surface wind speed. It alsoresults in an increase in the depth of the layer in whichsouth-easterly near-surface winds prevail, and in adecrease in the strength of the large-scale flow overthe continent, in particular in summer. In theescarpment region a decrease of z0m is foundto result in too high wind speeds. Surface temperatureson average decrease while atmospheric temperaturesincrease, resulting in an increase of near-surfacestatic stability. Changes in roughness lengths donot significantly change the temperature profiles.The surface fluxes, on average found reduced, aremodelled best by using the z0h based on thesurface renewal method. 相似文献
2.
《Geoforum》2016
This paper integrates insights from political ecology with a politics of scaling to discuss the construction and transformation of scalar topographies as part of the politics and power dynamics of natural resource management. The paper details two case studies from Community Based Natural Resource Management in the forest and wildlife sectors of Tanzania to: (1) analyse the devolution of power from the state to the local level; and (2) investigate the constant renegotiations and scalar transformations by actors across multiple levels in attempts to manipulate the governance system. The paper highlights the sociospatial aspects of the struggles and politics of natural resource management, and emphasises that whilst these processes of scalar negotiation and struggle are distinct between the two examples, they both revolve around the same political struggle over power. This indicates an important structuration element of power and scale as they are shaped by both the structural configuration of power within each sector alongside the agency of different actors across multiple levels. 相似文献
3.
4.
The relaxed eddy accumulation (REA) method allows the measurement of trace gas fluxes when no fast sensors are available for eddy covariance measurements. The flux parameterisation used in REA is based on the assumption of scalar similarity, i.e., similarity of the turbulent exchange of two scalar quantities. In this study changes in scalar similarity between carbon dioxide, sonic temperature and water vapour were assessed using scalar correlation coefficients and spectral analysis. The influence on REA measurements was assessed by simulation. The evaluation is based on observations over grassland, irrigated cotton plantation and spruce forest.Scalar similarity between carbon dioxide, sonic temperature and water vapour showed a distinct diurnal pattern and change within the day. Poor scalar similarity was found to be linked to dissimilarities in the energy contained in the low frequency part of the turbulent spectra ( < 0.01 Hz).The simulations of REA showed significant change in b-factors throughout the diurnal course. The b-factor is part of the REA parameterisation scheme and describes a relation between the concentration difference and the vertical flux of a trace gas. The diurnal course of b-factors for carbon dioxide, sonic temperature and water vapour matched well. Relative flux errors induced in REA by varying scalar similarity were generally below ± 10%. Systematic underestimation of the flux of up to − 40% was found for the use of REA applying a hyperbolic deadband (HREA). This underestimation was related to poor scalar similarity between the scalar of interest and the scalar used as proxy for the deadband definition. 相似文献
5.
A. Bhadra 《Astrophysics and Space Science》2007,310(1-2):169-172
Scalar tensor (ST) theories of gravitation contain an attractor mechanism towards general relativity. The mechanism is supposed
to start back at time of inflation. Consequently the characteristic coupling function of the ST theories could attain a very
large value during the radiation epoch. Here ST cosmology in the radiation dominated universe is studied under such situation.
A general solution of the scale factor in the radiation dominated flat universe is obtained that is characterized by an additional
degree of freedom. An implication of this extra parameter is discussed.
相似文献
6.
《Geoforum》2015
Based on insights from peasant and indigenous communities’ struggles for water in Andean Peru and Ecuador, in this article we argue that the defense of grassroots interests -and with it the advancement of more equitable governance- greatly hinges on the capacity of these groups to engage in grassroots scalar politics. With increasing pressure on water resources in the Andes, the access to water of many rural peasant and indigenous communities is being threatened. The growing realization that their access to water and related interests are embedded in broader regional and national politics, legal frameworks and water policies, has led many communities and peasant water user associations to engage in networks and create alliances with other water users, governmental institutions and non-governmental actors. To better understand these (and other) grassroots struggles and strategies, in this contribution we develop the concept of grassroots scalar politics, which we use as a lens to analyze two case studies. In Ecuador we present how water users of the province of Chimborazo have defended their interests through the consolidation of the Provincial Water Users Associations’ Federation Interjuntas-Chimborazo and its networks. Then we focus on how with the support of Interjuntas-Chimborazo the Water Users Association of the Chambo irrigation system defended their historical water allocation. In Peru we analyze the conformation and achievements of the federative Water Users Association of Ayacucho (JUDRA) and present how the community of Ccharhuancho in the region of Huancavelica, managed to defend its waters and territory against the coastal irrigation sector of Ica. 相似文献
7.
Axially symmetric cosmological models with cosmic string source are obtained in a scalar-tensor theory of gravitation proposed
by Saez and Ballester (Phys. Lett. A113, 467, 1985). The models obtained give us axially symmetric geometric (Nambu) string, p-string and Reddy string (Astrophys. Space Sci. 286, 2003b) in Saez-Ballester theory. Some physical properties of the models are also discussed. 相似文献
8.
Investigating a Hierarchy of Eulerian Closure Models for Scalar Transfer Inside Forested Canopies 总被引：3，自引：3，他引：0
Jehn-Yih Juang Gabriel G. Katul Mario B. Siqueira Paul C. Stoy Heather R. McCarthy 《Boundary-Layer Meteorology》2008,128(1):1-32
Modelling the transfer of heat, water vapour, and CO2 between the biosphere and the atmosphere is made difficult by the complex two-way interaction between leaves and their immediate microclimate. When simulating scalar sources and sinks inside canopies on seasonal, inter-annual, or forest development time scales, the so-called well-mixed assumption (WMA) of mean concentration (i.e. vertically constant inside the canopy but dynamically evolving in time) is often employed. The WMA eliminates the need to model how vegetation alters its immediate microclimate, which necessitates formulations that utilize turbulent transport theories. Here, two inter-related questions pertinent to the WMA for modelling scalar sources, sinks, and fluxes at seasonal to inter-annual time scales are explored: (1) if the WMA is to be replaced so as to resolve this two-way interaction, how detailed must the turbulent transport model be? And (2) what are the added predictive skills gained by resolving the two-way interaction vis-à-vis other uncertainties such as seasonal variations in physiological parameters. These two questions are addressed by simulating multi-year mean scalar concentration and eddy-covariance scalar flux measurements collected in a Loblolly pine (P. taeda L.) plantation near Durham, North Carolina, U.S.A. using turbulent transport models ranging from K-theory (or first-order closure) to third-order closure schemes. The multi-layer model calculations with these closure schemes were contrasted with model calculations employing the WMA. These comparisons suggested that (i) among the three scalars, sensible heat flux predictions are most biased with respect to eddy-covariance measurements when using the WMA, (ii) first-order closure schemes are sufficient to reproduce the seasonal to inter-annual variations in scalar fluxes provided the canonical length scale of turbulence is properly specified, (iii) second-order closure models best agree with measured mean scalar concentration (and temperature) profiles inside the canopy as well as scalar fluxes above the canopy, (iv) there are no clear gains in predictive skills when using third-order closure schemes over their second-order closure counterparts. At inter-annual time scales, biases in modelled scalar fluxes incurred by using the WMA exceed those incurred when correcting for the seasonal amplitude in the maximum carboxylation capacity (V cmax, 25) provided its mean value is unbiased. The role of local thermal stratification inside the canopy and possible computational simplifications in decoupling scalar transfer from the generation of the flow statistics are also discussed.
相似文献
“The tree, tilting its leaves to capture bullets of light; inhaling, exhaling; its many thousand stomata breathing, creating the air”. Ruth Stone, 2002, In the Next Galaxy
9.
We test a surface renewal model that is widely used over snow and ice surfaces to calculate the scalar roughness length (z s ), one of the key parameters in the bulk aerodynamic method. For the first time, the model is tested against observations that cover a wide range of aerodynamic roughness lengths (z 0). During the experiments, performed in the ablation areas of the Greenland ice sheet and the Vatnajökull ice cap in Iceland, the surface varied from smooth snow to very rough hummocky ice. Over relatively smooth snow and ice with z 0 below a threshold value of approximately 10?3 m, the model performs well and in accord with earlier studies. However, with growing hummock size, z 0 increases well above the threshold and the bulk aerodynamic flux becomes significantly smaller than the eddy-correlation flux (e.g. for z 0 = 0.01 m, the bulk aerodynamic flux is about 50% smaller). Apparently, the model severely underpredicts z s over hummocky ice. We argue that the surface renewal model does not account for the deep inhomogeneous roughness sublayer (RSL) that is generated by the hummocks. As a consequence, the homogeneous substrate ice grain cover becomes more efficiently ‘ventilated’. Calculations with an alternative model that includes the RSL and was adapted for use over hummocky ice, qualitatively confirms our observations. We suggest that, whenever exceedance of the threshold occurs (z 0 > 10?3 m, i.e., an ice surface covered with at least 0.3-m high hummocks), the following relation should be used to calculate scalar roughness lengths, ln (z s /z 0) = 1.5 ? 0.2 ln (Re *) ? 0.11(ln (Re *))2. 相似文献
10.
The joint probability density function (PDF) of turbulent velocity and concentration of a passive scalar in an urban street
canyon is computed using a newly developed particle-in-cell Monte Carlo method. Compared to moment closures, the PDF methodology
provides the full one-point one-time PDF of the underlying fields containing all higher moments and correlations. The small-scale
mixing of the scalar released from a concentrated source at the street level is modelled by the interaction by exchange with
the conditional mean (IECM) model, with a micro-mixing time scale designed for geometrically complex settings. The boundary
layer along no-slip walls (building sides and tops) is fully resolved using an elliptic relaxation technique, which captures
the high anisotropy and inhomogeneity of the Reynolds stress tensor in these regions. A less computationally intensive technique
based on wall functions to represent the boundary layers and its effect on the solution are also explored. The calculated
statistics are compared to experimental data and large-eddy simulation. The present work can be considered as the first example
of computation of the full joint PDF of velocity and a transported passive scalar in an urban setting. The methodology proves
successful in providing high level statistical information on the turbulence and pollutant concentration fields in complex
urban scenarios. 相似文献