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R. S. Quiroz 《Pure and Applied Geophysics》1980,118(1):416-427
Zonal mean data and amplitudes and phases of planetary zonal waves were derived from daily hemispheric maps for tropospheric and stratospheric levels, for the four winters 1975–76 to 1978–79. Important year-to-year fluctuation in zonal means and wave activity are described, most notable of which are the changes from 1975–76 to 1976–77. Comparison of the relative strengths of the stratospheric and tropospheric jet streams shows a strong negative correlation (–0.8) between monthly mean zonal stratospheric winds (at 10 mb, 65°N) and zonal tropospheric winds (at 200 mb, 32.5°N, in the jet core) and a positive correlation (+0.7) between the stratospheric 10 mb winds and the tropospheric 200 mb winds at 65°N. Parameters correlated were the departures from the climatological mean zonal winds. The structure of correlation between wave amplitudes in the same wave number (1, 2) at different altitudes and between wave numbers 1 and 2 is investigated. We find a high correlation (+0.93) between wave 1 in the stratosphere (10 mb height) and wave 2 (height) in the troposphere at 65°N; but only a weak correlation (+0.2) between wave 1 amplitudes in the stratosphere and troposphere. These results suggest the possible importance of wave-wave interactions in processes linking the stratosphere and troposphere. The wave correlations presented here are based on comparisons of monthly means of daily amplitudes; the correlation structure in individual wave developments may differ, in view of the likelihood of altitudinal lags in wave amplification. 相似文献
994.
Krista L. Jones Geoffrey C. Poole William W. Woessner Matt V. Vitale Brian R. Boer Scott J. O'Daniel Steven A. Thomas Brook A. Geffen 《水文研究》2008,22(13):2105-2113
Across 1·7 km2 of the Umatilla River floodplain (Oregon, USA), we investigated the influences of an ephemeral tributary and perennial ‘spring channel’ (fed only by upwelling groundwater) on hyporheic hydrology. We derived maps of winter and summer water‐table elevations from data collected at 46 monitoring wells and 19 stage gauges and used resulting maps to infer groundwater flow direction. Groundwater flow direction varied seasonally across the floodplain and was influenced by main channel stage, flooding, the tributary creek, and the location and direction of hyporheic exchange in the spring channel. Hyporheic exchange in the spring channel was evaluated with a geochemical mixing model, which confirmed patterns of floodplain groundwater movement inferred from water‐table maps and showed that the spring channel was fed predominantly by hyporheic water from the floodplain aquifer (87% during winter, 80% during summer), with its remaining flow supplied by upslope groundwater from the adjacent catchment aquifer. Summertime growth of aquatic macrophytes in the spring channel also influenced patterns of hyporheic exchange and groundwater flow direction in the alluvial aquifer by increasing flow resistance in the spring channel, locally raising surface water stage and adjacent water‐table elevation, and thereby altering the slope of the water‐table in the hyporheic zone. The Umatilla River floodplain is larger than most sites where hyporheic hydrology has been investigated in detail. Yet, our results corroborate other research that has identified off‐channel geomorphic features as important drivers of hyporheic hydrology, including previously published modeling efforts from a similar river and field observations from smaller streams. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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M. A. Fardal P. Guhathakurta A. Babul A. W. McConnachie 《Monthly notices of the Royal Astronomical Society》2007,380(1):15-32
Published maps of red giant stars in the halo region of M31 exhibit a giant stellar stream to the south of this galaxy, as well as a giant 'shelf' to the northeast of M31's centre. Using these maps, we find that there is a fainter shelf of comparable size on the western side as well. By choosing appropriate structural and orbital parameters for an accreting dwarf satellite within the accurate M31 potential model of Geehan et al., we produce a very similar structure in an N -body simulation. In this scenario, the tidal stream produced at pericentre of the satellite's orbit matches the observed southern stream, while the forward continuation of this tidal stream makes up two orbital loops, broadened into fan-like structures by successive pericentric passages; these loops correspond to the north-eastern and western shelves. The tidal debris from the satellite also reproduces a previously observed 'stream' of counterrotating planetary nebulae and a related stream seen in red giant stars. The debris pattern in our simulation resembles the shell systems detected around many elliptical galaxies, though this is the first identification of a shell system in a spiral galaxy and the first in any galaxy close enough to allow measurements of stellar velocities and relative distances. We discuss the physics of these partial shells, highlighting the role played by spatial and velocity caustics in the observations. We show that kinematic surveys of the tidal debris will provide a sensitive measurement of M31's halo potential, while quantifying the surface density of debris in the shelves will let us reconstruct the original mass and time of disruption of the progenitor satellite. 相似文献
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Understanding the interaction of tides and waves is essential in many studies, including marine renewable energy, sediment transport, long-term seabed morphodynamics, storm surges and the impacts of climate change. In the present research, a COAWST model of the NW European shelf seas has been developed and applied to a number of physical processes. Although many aspects of wave–current interaction can be investigated by this model, our focus is on the interaction of barotropic tides and waves at shelf scale. While the COWAST model was about five times more computationally expensive than running decoupled ROMS (ocean model) and SWAN (wave model), it provided an integrated modelling system which could incorporate many wave–tide interaction processes, and produce the tide and wave parameters in a unified file system with a convenient post-processing capacity. Some applications of the model such as the effect of tides on quantifying the wave energy resource, which exceeded 10% in parts of the region, and the effect of waves on the calculation of the bottom stress, which was dominant in parts of the North Sea and Scotland, during an energetic wave period are presented, and some challenges are discussed. It was also shown that the model performance in the prediction of the wave parameters can improve by 25% in some places where the wave-tide interaction is significant. 相似文献
1000.
Vegetation succession in deglaciated landscapes: implications for sediment and landscape stability 下载免费PDF全文
Megan J. Klaar Chris Kidd Edward Malone Rebecca Bartlett Gilles Pinay F. Stuart Chapin Alexander Milner 《地球表面变化过程与地形》2015,40(8):1088-1100
Landscapes exposed by glacial retreat provide an ideal natural laboratory to study the processes involved in transforming a highly disturbed, glacially influenced landscape to a stable, diverse ecosystem which supports numerous species and communities. Large‐scale vegetation development and changes in sediment availability, used as a proxy for paraglacial adjustment following rapid deglaciation, were assessed using information from remote sensing. Delineation of broad successional vegetation cover types was undertaken using Landsat satellite imagery (covering a 22 year period) to document the rate and trajectory of terrestrial vegetation development. Use of a space‐for‐time substitution in Glacier Bay National Park, Alaska, allowed ‘back‐calculation’ of the age and stage of development of six catchments over 206 years. The high accuracy (89.2%) of the remotely sensed information used in monitoring successional change allowed detection of a high rate of change in vegetation classes in early successional stages (bare sediment and alder). In contrast, later successional stages (spruce and spruce–hemlock dominated forest) had high vegetation class retention, and low turnover. Modelled rates of vegetation change generally confirmed the estimated rates of successional turnover previously reported. These data, when combined with the known influence of terrestrial succession on soil development and sediment availability, suggest how physical and biological processes interact over time to influence paraglacial adjustment following deglaciation. This study highlights the application of remote sensing of successional chronosequence landscapes to assess the temporal dynamics of paraglacial adjustment following rapid deglaciation and shows the importance of incorporating bio‐physical interactions within landscape evolution models. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献