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排序方式: 共有165条查询结果,搜索用时 15 毫秒
61.
David Valença Dantas Mario Barletta André Ricardo Araújo Lima Jonas de Assis Almeida Ramos Monica Ferreira da Costa Ulrich Saint-Paul 《Estuaries and Coasts》2012,35(2):587-602
The seasonal and spatial distribution (density and biomass) of five size classes of two catfish species (Cathorops spixii and Cathorops agassizii) were studied along an estuarine ecocline to test the relative importance of the nursery function of each habitat. Seasonal
vs. area interactions were significant for all size classes of both species. During the early rainy season, the middle estuary
is an important nursery habitat for juveniles of both species. When environmental conditions change during the late rainy
season, the C. spixii primary nursery habitat shifts to the lower estuary. During this period, juveniles of C. agassizii remain in the middle estuary. Another important ecological area is the upper estuary, which becomes a breeding, spawning
and hatchery area during the late dry season for both species. The nursery function of habitats shifts according to the seasonal
fluctuation of salinity and dissolved oxygen, and each species responds differently to this change. 相似文献
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A multi‐method field experiment to determine local groundwater flow in a glacier forefield 下载免费PDF全文
Florian Kobierska Tobias Jonas Nena Griessinger Christian Hauck Stephan Huxol Stefano M. Bernasconi 《水文研究》2015,29(6):817-827
We implemented multiple independent field techniques to determine the direction and velocity of groundwater flow at a specific stream reach in a glacier forefield. Time‐lapse experiments were conducted using two electrical resistivity tomography (ERT) lines installed in a cross pattern. A circular array of groundwater tubes was also installed to monitor groundwater flow via discrete salt injections. Both inter‐borehole and ERT results confirmed this stream section as a losing reach and enabled quantification of the flow direction. Both techniques yielded advection velocities varying between 5.7 and 21.8 m/day. Estimates of groundwater flow direction and velocity indicated that groundwater infiltrates from the stream nearby and not from the adjacent lateral moraine. Groundwater age estimated from radon concentration measurements supported this hypothesis. Despite uncertainties inherent to each of the methods deployed, the combination of multiple field techniques allowed drawing consistent conclusions about local groundwater flow. We thus regard our multi‐method approach as a reliable way to characterize the two‐dimensional groundwater flow at sites where more invasive groundwater investigation techniques are difficult to carry out and local heterogeneities can make single measurements unreliable. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
64.
Jonas B. Ruh 《地学学报》2016,28(3):163-170
Seamounts entering active subduction zone trenches initially collide with the frontal sedimentary accretionary wedges resulting in severe deformation of the overriding plate. A typical feature of this deformation is the occurrence of submarine landslides due to gravitational instabilities. Such landslides have been reported from the Middle America and Hikurangi trenches and potentially generate tsunami waves. Yet, the dynamics of accretionary wedges during seamount indentation, and landsliding as a mechanical response in particular, have not been investigated qualitatively. Here, I use 3D high‐resolution numerical experiments to model the collision of conical and flat‐topped seamounts into accreting sedimentary sequences. Results show that the topographical evolution of an accretionary wedge mainly depends on the volume of the entering seamount and not on its height. Submarine landslides occur only if seamounts are not completely buried by the sedimentary sequence, and the volume of the avalanche is roughly correlated with the seamount volume overtopping the incoming sediments. 相似文献
65.
E. Raschke P. Flamant Y. Fouquart P. Hignett H. Isaka P. R. Jonas H. Sundquist P. Wendling 《Surveys in Geophysics》1998,19(2):89-138
The dominant role of clouds in modulating and interacting with radiative energy transports within the atmosphere, in providing precipitation, transporting water and influencing air-chemical processes is still not understood well enough to be accurately represented within atmospheric circulation and climate models over all regions of the globe. Also the extraction of real-world cloud properties from satellite measurements still contains uncertainties. Therefore, various projects have been developed within the Global Energy and Water Cycle Experiment (GEWEX), to achieve more accurate solutions for this problem by direct measurements within cloud fields and other complementary studies. They are based on the hypothesis, that most relevant properties of cloud fields can be parametrized on the basis of the prognostic field variables of atmospheric circulation models, and that the cloud microphysical properties can directly be related – with additional parameters on the particle shapes etc. – to the radiative transfer properties.One of these projects has been the European Cloud and Radiation Experiment (EUCREX) with its predecessor ICE (International Cirrus Experiment).The EUCREX and ICE provided a common platform for research groups from France, Germany, Sweden and the United Kingdom to concentrate their efforts primarily on high, cold cirrus. They showed, with data from satellites, that this cloud species enhances the atmospheric greenhouse-effect. Numerical mesoscale models were used in sensitivity studies on cloud developments. In-situ measurements of cloud properties were made during more than 30 aircraft missions, where also in-flight comparisons of various instruments were made to ensure the quality of data sets measured from different aircraft. The particle sampling probes, used for in-cloud measurements, showed a disagreement in total number density in all ranges between about 20–50%, while all other instruments agreed quite satisfactorily. A few measured holographic data provided information on typical ice-crystal shapes, which were used in numerical simulations of their absorption and scattering properties.Several new instruments for both in-situ and remote measurement, such as a polar nephelometer, a chopped pyrgeometer and an imaging multispectral polarimeter (POLDER) for cloud and radiation measurements were tested and improved. New algorithms were developed for cloud classifications in multispectral satellite images and also for simulations of the scattering of radiation by non-spherical particles.This paper primarily summarizes the EUCREX results obtained between 1989 and 1996, and provides examples of the many results which have been obtained so far. It is not a complete review of the world-wide state in this field, but it tries to place the EUCREX results into the world-wide development. Therefore many references are made to the results of other groups, which in turn influenced the work within EUCREX. 相似文献
66.
Ice crystal clouds have an influence on the radiative budget of the earth; however, the exact size and nature of this influence has yet to be determined. A laboratory cloud chamber experiment has been set up to provide data on the optical scattering behaviour of ice crystals at a visible wavelength in order to gain information which can be used in climate models concerning the radiative characteristics of cirrus clouds. A PMS grey-scale probe is used to monitor simultaneously the cloud microphysical properties in order to correlate these closely with the observed radiative properties. Preliminary results show that ice crystals scatter considerably more at 90° than do water droplets, and that the halo effects are visible in a laboratorygenerated cloud when the ice crystal concentration is sufficiently small to prevent masking from multiple scattering. 相似文献
67.
da Silveira Lucas Cardoso de Oliveira Amauri Pereira Sánchez Maciel Piñero Codato Georgia Ferreira Maurício Jonas Filho Edson Pereira Marques Božnar Marija Zlata Mlakar Primož 《Boundary-Layer Meteorology》2022,185(2):197-197
Boundary-Layer Meteorology - 相似文献
68.
69.
Melt water driven stream and groundwater stage fluctuations on a glacier forefield (Dammagletscher,Switzerland) 下载免费PDF全文
Jan Magnusson Florian Kobierska Stephan Huxol Masaki Hayashi Tobias Jonas James W. Kirchner 《水文研究》2014,28(3):823-836
In many mountain regions, large land areas with heterogeneous soils have become ice‐free with the ongoing glacier retreat. On these recently formed proglacial fields, the melt of the remaining glaciers typically drives pronounced diurnal stream level fluctuations that propagate into the riparian zone. This behaviour was measured on the Damma glacier forefield in central Switzerland with stage recorders in the stream and groundwater monitoring wells along four transects. In spite of the large groundwater stage variations, radon measurements in the near‐stream riparian zone indicate that there is little mixing between stream water and groundwater on daily time scales. At all four transects, including both losing and gaining reaches, the groundwater level fluctuations lagged the stream stage variations and were often damped with distance from the stream. Similar behaviours have been modelled using the diffusion equation in coastal regions influenced by tidal sea level variations. We thus tested the ability of such a model to predict groundwater level fluctuations in proglacial fields. The model reproduced several key features of the observed fluctuations at three of four locations, although discrepancies also arise due to non representative input data and model simplifications. Nevertheless, calibration of the model for the individual transects yielded realistic estimates of hydraulic diffusivities between the stream and groundwater monitoring wells. We conclude that studying diurnal groundwater fluctuations can provide important information about the subsurface hydrology of alpine watersheds dominated by glacier melt. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
70.
Abstract A simple way to model stratification of the ocean or atmosphere is in terms of two superposed homogeneous layers of different density. Effects of cooling of the upper layer, such as that which occurs during bottom-water formation in the ocean, can be simulated by mass transfer from the upper layer to the lower layer. A model is constructed to see What effect such a mass transfer has on the flow when the mass transfer is confined to a limited region. The main effects are (i) doming of the interface, which maintains pressure gradients in balance with the velocity field, (ii) cyclonic rotation in the upper layer due to conservation of angular momentum of particles king drawn toward the sink, yet anticyclonic vorticity for those particles outside the mass transfer region due to shrinking of vortex lines drawn up over the dome. (iii) generally anticyclonic rotation in the lower layer due to particles tending to maintain their angular momentum while being pushed outwards, but some cyclonic rotation near the centre of mass transfer, due to momentum transfer from the upper layer. Similar effects to these are seen in the Greenland Sea where bottom water formation occurs. Results of the same sort are also found in a laboratory model of the process. 相似文献