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21.
Nathan E. Miller Rob Stoll Walter F. Mahaffee Eric R. Pardyjak 《Boundary-Layer Meteorology》2017,165(1):113-143
Flow physics is investigated in a two-dimensional trellised agricultural canopy to examine that architecture’s unique signature on turbulent transport. Analysis of meteorological data from an Oregon vineyard demonstrates that the canopy strongly influences the flow by channelling the mean flow into the vine-row direction regardless of the above-canopy wind direction. Additionally, other flow statistics in the canopy sub-layer show a dependance on the difference between the above-canopy wind direction and the vine-row direction. This includes an increase in the canopy displacement height and a decrease in the canopy-top shear length scale as the above-canopy flow rotates from row-parallel towards row-orthogonal. Distinct wind-direction-based variations are also observed in the components of the stress tensor, turbulent kinetic energy budget, and the energy spectra. Although spectral results suggest that sonic anemometry is insufficient for resolving all of the important scales of motion within the canopy, the energy spectra peaks still exhibit dependencies on the canopy and the wind direction. These variations demonstrate that the trellised-canopy’s effect on the flow during periods when the flow is row-aligned is similar to that seen by sparse canopies, and during periods when the flow is row-orthogonal, the effect is similar to that seen by dense canopies. 相似文献
22.
The eighth part of the catalogue of Shakhbazian groups contains the positions and references of all the galaxies of the following 48 groups (north of δ > + 2°30'): Shkh 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 207, 208, 209, 210, 211, 212, 213, 214, 215. For the estimation of the coordinates the Digitized Sky Survey was used. 相似文献
23.
The nineth part of the catalogue of Shakhbazian groups contains the positions and references of all the galaxies of the following 48 groups (north of δ < +2°30'): Shkh 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 253, 254, 255, 256, 257, 258, 259, 260, 328, 338, 339, 340, 340a. For the estimation of the coordinates the Digitized Sky Survey was used. 相似文献
24.
Fernando Gázquez José María Calaforra Paolo Forti Heather Stoll Bassam Ghaleb Antonio Delgado‐Huertas 《地球表面变化过程与地形》2014,39(10):1345-1353
Speleothems are usually composed of thin layers of calcite (or aragonite). However, cemented detrital materials interlayered between laminae of speleothemic carbonate have been also observed in many caves. Flowstones comprising discontinuous carbonate layers form due to flowing water films, while flood events introduce fluviokarstic sediments in caves that, on occasion, are recorded as clayey layers inside flowstones and stalagmites. This record provides a potential means of understanding the frequency of palaeofloods using cave records. In this work, we investigate the origin of this type of detrital deposit in El Soplao Cave (Northern Spain). The age of the lowest aragonite layer of a flowstone reveals that the earliest flood period occurred before 500 ka, though most of the flowstone formed between 422 +69/‐43 ka and 400 +66/‐42 ka. This suggests that the cave was periodically affected by palaeoflood events that introduced detrital sediments from the surface as a result of occasional extreme rainfall events, especially at around 400 ka. The mineralogical data enable an evolutionary model for this flowstone to be generated based on the alternation of flood events with laminar flows and carbonate layers precipitation that can be extrapolated to other caves in which detrital sediments inside speleothems have been found. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
25.
26.
Geometric characteristics and evolution of a tidal channel network in experimental setting 总被引:3,自引:0,他引:3
This paper reports on a laboratory study that aims to reproduce a tidal channel network, in order to enhance the understanding of the morphodynamic evolution of the channel characteristics as the network expands and finally reaches equilibrium. A high‐resolution laser system scanned the bed topography at different time steps creating multiple digital elevation models of the channel network. Two hundred and seventy individual channel segments are analyzed and cross‐correlated in terms of their width, depth and length. The laboratory results show positive linear correlations between depth and width as well as between length and width of channel segments of the network configuration at final equilibrium. In a downstream direction, channels appear to widen more than they deepen, indirectly a sign that discharge has a stronger control on channel width than on depth. In contrast to fluvial drainage networks that commonly display fractal and scale‐invariant behavior, the geometric properties of the experimental tidal creek network shows scale dependence. Channel attributes exhibit consistent patterns of exponentially decreasing abundance, with increasing creek length, depth and width. The nature of the observed exponential distributions within creek attributes (width, depth, length) allows for statistical predictability of relative creek attribute dimensions downstream and through time. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
27.
Bernhard Krautzer Wilhelm Graiss Giovanni Peratoner Christian Partl Sonia Venerus Brigitte Klug 《Natural Hazards》2011,56(2):547-557
Control of erosion, and all of its after effects, from increased surface drainage and erosion to the formation of karst, is
one of the essential problems when undertaking recultivation following necessary interventions in the sub-alpine and alpine
vegetation stage (high zones). Average slope inclinations of 30–45% in the vicinity of ski runs, and far above in areas of
natural erosion and avalanche zones, make restoration processes with sufficient erosion protection the prerequisite for success.
Only a sufficient vegetation development of more than 70% ground cover stabilises the topsoil in the long term and reduces
soil erosion to an acceptable degree. From 1999 to 2002, an international EU project with the participation of research groups
and private firms from Austria, Italy and Germany was carried out under the direction of the Agricultural Research and Education
Centre Raumberg-Gumpenstein (AREC) on five different Alpine sites at altitudes from 1,245 to 2,350 m above sea level. The
aim of the work was the formulation of practice-relevant requirements for recultivation following intervention in high zones,
especially following constructional measures in the vicinity of ski runs and lifts, torrent- and avalanche barriers. In a
statistical comparison, the relationship between restoration techniques, seed mixtures of differing ecological value and vegetation
cover was observed. The influence of application technique on erosion processes after restoration was obvious for the first
two vegetation periods. Only with the additional use of mulch covers could increase surface drainage and noticeable soil loss
be avoided. At high altitudes, the choice of seed mixture, irrespective of whether rapid or slow growing and independent of
the extent of accompanying fertilisation, had no significance in the first two vegetation periods following sowing. In the
following growing seasons, however, higher cover values were obtained with site-specific seed mixtures at three of the five
experimental sites. While few species of the commercial seed mixture showed satisfactory persistency, most of the grasses
and in particular the alpine leguminosae of site-specific seed mixtures increased their share during the observation period.
In the long-term, sufficient protection against erosion is only guaranteed by the use of stable, enduring and ecologically
adapted species. 相似文献
28.
The coupled δ13C-radiocarbon systematics of three European stalagmites deposited during the Late Glacial and early Holocene were investigated to understand better how the carbon isotope systematics of speleothems respond to climate transitions. The emphasis is on understanding how speleothems may record climate-driven changes in the proportions of biogenic (soil carbon) and limestone bedrock derived carbon. At two of the three sites, the combined δ13C and 14C data argue against greater inputs of limestone carbon as the sole cause of the observed shift to higher δ13C during the cold Younger Dryas. In these stalagmites (GAR-01 from La Garma cave, N. Spain and So-1 from Sofular cave, Turkey), the combined changes in δ13C and initial 14C activities suggest enhanced decomposition of old stored, more recalcitrant, soil carbon at the onset of the warmer early Holocene. Alternative explanations involving gradual temporal changes between open- and closed-system behaviour during the Late Glacial are difficult to reconcile with observed changes in speleothem δ13C and the growth rates. In contrast, a stalagmite from Pindal cave (N. Spain) indicates an abrupt change in carbon inputs linked to local hydrological and disequilibrium isotope fractionation effects, rather than climate change. For the first time, it is shown that while the initial 14C activities of all three stalagmites broadly follow the contemporaneous atmospheric 14C trends (the Younger Dryas atmospheric 14C anomaly can be clearly discerned), subtle changes in speleothem initial 14C activities are linked to climate-driven changes in soil carbon turnover at a climate transition. 相似文献
29.
30.
Marc-Philippe Stoll 《Surveys in Geophysics》2000,21(2-3):133-146
In the first part of this tutorial paper, we survey the physical basis of radiometry – the measurement of electromagnetic energy, and the physical quantities needed to quantify it and to describe reflected and emitted radiation The second part considers what a radiometer is, how it works and on what the signal depends. The third part addresses radiometry inthe context of Earth Observations, with an emphasis on the solar reflected region (visible near infrared) and thermal infrared region. The role of the atmosphere, the ambient radiation, and how to extract information from the signal at the satellite are also discussed briefly. 相似文献