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271.
Erik Gómez-Baggethun Victoria Reyes-García Per Olsson Carlos Montes 《Global Environmental Change》2012,22(3):640-650
Research in the last decade has emphasised the potential contribution of traditional ecological knowledge to cope with challenges from global environmental change. This research examines the role of traditional ecological knowledge and shared systems of beliefs in building long-term social–ecological resilience to environmental extremes. Data were collected from 13 villages of the Doñana region, southwestern Spain, through interviews, focus groups, and systematic reviews of historical archives. First, we assess adaptive practices to cope with environmental change. Then, we use historical records of religious ceremonies (1577–1956) to reconstruct collective responses to environmental extremes. Our results (1) show how environmental extremes could induce social and economic crises through declines in ecosystem services and (2) identify practices to cope with recurrent disturbance and institutional devices developed in response to environmental extremes. We conclude that traditional ecological knowledge and shared systems of beliefs can facilitate collective responses to crises and contribute to the maintenance of long-term resilience of social–ecological systems. 相似文献
272.
Aquifer Vulnerability Assessment Based on Sequence Stratigraphic and 39Ar Transport Modeling
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Torben O. Sonnenborg Peter B. Scharling Klaus Hinsby Erik S. Rasmussen Peter Engesgaard 《Ground water》2016,54(2):214-230
A large‐scale groundwater flow and transport model is developed for a deep‐seated (100 to 300 m below ground surface) sedimentary aquifer system. The model is based on a three‐dimensional (3D) hydrostratigraphic model, building on a sequence stratigraphic approach. The flow model is calibrated against observations of hydraulic head and stream discharge while the credibility of the transport model is evaluated against measurements of 39Ar from deep wells using alternative parameterizations of dispersivity and effective porosity. The directly simulated 3D mean age distributions and vertical fluxes are used to visualize the two‐dimensional (2D)/3D age and flux distribution along transects and at the top plane of individual aquifers. The simulation results are used to assess the vulnerability of the aquifer system that generally has been assumed to be protected by thick overlaying clayey units and therefore proposed as future reservoirs for drinking water supply. The results indicate that on a regional scale these deep‐seated aquifers are not as protected from modern surface water contamination as expected because significant leakage to the deeper aquifers occurs. The complex distribution of local and intermediate groundwater flow systems controlled by the distribution of the river network as well as the topographical variation (Tóth 1963) provides the possibility for modern water to be found in even the deepest aquifers. 相似文献
273.
274.
Erik ASPHAUG 《Meteoritics & planetary science》2008,43(6):1075-1084
Abstract— If impact stress reverberation is the primary gradational process on an asteroid at global scales, then the largest undegraded crater records an asteroid's seismological response. The critical crater diameter Dcrit is defined as the smallest crater whose formation disrupts all previous craters globally up to its size; it is solved for by combining relationships for crater growth and for stress attenuation. The computation for Dcrit gives a simple explanation for the curious observation that small asteroids have only modest undegraded craters, in comparison to their size, whereas large asteroids have giant undegraded craters. Dcrit can even exceed the asteroid diameter, in which case all craters are “local” and the asteroid becomes crowded with giant craters. Dcrit is the most recent crater to have formed on a blank slate; when it is equated to the measured diameter of the largest undegraded crater on known asteroids, peak particle velocities are found to attenuate with the 1.2–1.3 power of distance—less attenuative than strong shocks, and more characteristic of powerful seismic disturbances. This is to be expected, since global degradation can result from seismic (cm s?1) particle velocities on small asteroids. Attenuation, as modeled, appears to be higher on asteroids known to be porous, although these are also bodies for which different crater scaling rules might apply. 相似文献
275.
276.
Göran Broström Kai H. Christensen Magnus Drivdal Jan Erik H. Weber 《Ocean Dynamics》2014,64(7):1039-1045
In this study, we consider the origin of the Coriolis-Stokes (CS) force in the wave-averaged momentum and energy equations and make a short analysis of possible energy input to the ocean circulation (i.e., Eulerian mean velocity) from the CS force. Essentially, we find that the CS force appears naturally when considering vertically integrated quantities and that the CS force will not provide any energy input into the system for this case. However, by including the “Hasselmann force”, we show some inconsistencies regarding the vertical structure of the CS force in the Eulerian framework and find that there is a distinct vertical structure of the energy input and that the net input strongly depends on whether the wave zone is included in the analysis or not. We therefore question the introduction of the “Hasselmann force” into the system of equations, as the CS force appears naturally in the vertically integrated equations or when Lagrangian vertical coordinates are used. 相似文献
277.
Erik R. Urbach 《Planetary and Space Science》2009,57(7):880-74
Impact craters are among the most studied geomorphic planetary features because they yield information about the past geological processes and provide a tool for measuring relative ages of observed geologic formations. Surveying impact craters is an important task which traditionally has been achieved by means of visual inspection of images. The shear number of smaller craters present in high resolution images makes visual counting of such craters impractical. In this paper we present a method that brings together a novel, efficient crater identification algorithm with a data processing pipeline; together they enable a fully automatic detection of sub-km craters in large panchromatic images. The technical details of the method are described and its performance is evaluated using a large, 12.5 m/pixel image centered on the Nanedi Valles on Mars. The detection percentage of the method is ∼70%. The system detects over 35,000 craters in this image; average crater density is , but localized spots of much higher crater density are present. The method is designed to produce “million craters” global catalogs of sub-km craters on Mars and other planets wherever high resolution images are available. Such catalogs could be utilized for deriving high spatial resolution and high temporal precision stratigraphy on regional or even planetary scale. 相似文献
278.
Using field measurements we evaluate a previously deduced semi-empirical model for the dampening of temperature fluctuations
in a circular tube. The measurements show that the model is a reasonably good approximation, and the previous recommendation
of using a tube length of the order of 1,000 times the inner diameter of the tube to remove most of the temperature fluctuations
seems to hold. Part of the difference between the empirical results and the model is possibly due to deviations from the idealized
conditions assumed in the model such as no inclusion of the influence from the ambient atmospheric stability. Limitations
of the measurements are also likely to affect the evaluation. 相似文献
279.
Results from large-eddy simulations and field measurements have previously shown that the velocity field is influenced by
the boundary layer height, z
i
, during close to neutral, slightly unstable, atmospheric stratification. During such conditions the non-dimensional wind
profile, φ
m
, has been found to be a function of both z/L and z
i
/L. At constant z/L, φ
m
decreases with decreasing boundary layer height. Since φ
m
is directly related to the parameterizations of the air–sea surface fluxes, these results will have an influence when calculating
the surface fluxes in weather and climate models. The global impact of this was estimated using re-analysis data from 1979
to 2001 and bulk parameterizations. The results show that the sum of the global latent and sensible mean heat fluxes increase
by 0.77 W m−2 or about 1% and the mean surface stress increase by 1.4 mN m−2 or 1.8% when including the effects of the boundary layer height in the parameterizations. However, some regions show a larger
response. The greatest impact is found over the tropical oceans between 30°S and 30°N. In this region the boundary layer height
influences the non-dimensional wind profile during extended periods of time. In the mid Indian Ocean this results in an increase
of the mean annual heat fluxes by 2.0 W m−2 and an increase of the mean annual surface stress by 2.6 mN m−2. 相似文献
280.
Spectra of CO<Subscript>2</Subscript> and Water Vapour in the Marine Atmospheric Surface Layer 总被引:1,自引:1,他引:0
Erik Sahlée Ann-Sofi Smedman Anna Rutgersson Ulf Högström 《Boundary-Layer Meteorology》2008,126(2):279-295
Spectra of CO2 and water vapour fluctuations from measurements made in the marine atmospheric surface layer have been analyzed. A normalization
of spectra based on Monin–Obukhov similarity theory, originally developed for wind speed and temperature, has been successfully
extended also to CO2 and humidity spectra. The normalized CO2 spectra were observed to have somewhat larger contributions from low frequencies compared to humidity spectra during unstable
stratification. However, overall, the CO2 and humidity spectra showed good agreement as did the cospectra of vertical velocity with water vapour and CO2 respectively. During stable stratification the spectra and cospectra displayed a well-defined spectral gap separating the
mesoscale and small-scale turbulent fluctuations. Two-dimensional turbulence was suggested as a possible source for the mesoscale
fluctuations, which in combination with wave activity in the vertical wind is likely to explain the increase in the cospectral
energy for the corresponding frequency range. Prior to the analysis the turbulence time series of the density measurements
were converted to time series of mixing ratios relative to dry air. Some differences were observed when the spectra based
on the original density measurements were compared to the spectra based on the mixing ratio time series. It is thus recommended
to always convert the density time series to mixing ratio before performing spectral analysis. 相似文献