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71.
Jean-Marc Lardeaux Jean-Michel Caron Pascal Nisio Guy Pquignot Micheline Boudeulle 《Lithos》1986,19(3-4):187-203
Two Alpine eclogite bodies, sampled in metaophiolitic complexes of the Piemonte Zone, have been studied for geothermometry. It is demonstrated that temperature estimates, by both exchange thermometry and sizes of antiphase domains in omphacites, give rise to erratic results when the defect structures of the minerals are not taken into account. Microstructural criteria, by means of both optical and TEM microscopy, for reliable thermometry in low-temperature eclogites are disscussed. The dynamically recrystallized grains are the more suitable sites for the application of exchange thermometry, while only low-strained omphacites can be used for thermometry based on APD's. 相似文献
72.
73.
In the eclogitic micaschists of the Monte Mucrone area (Sesia-Lanzo zone, Italian Western Alps), we have measured in detail the eclogitic lineation at several outcrops. We present observations at the markers scale, this scale allowing the whole range of progressive deformations to be described. Populations of glaucophanes and jadeites show different statistical features which must be, at least for a part, produced by the distinct mechanical behavior for these markers during the alpine history. The glaucophanes show a positive correlation between the intensity of preferred orientation and their aspect ratio, due to a mainly rigid behavior. The observed differences in shape and orientation of jadeites also show different behavior, related to different retromorphic overprints. We briefly discuss the implications of these observations on the significance of metamorphic lineations. 相似文献
74.
Rudolf Brázdil Rüdiger Glaser Christian Pfister Petr Dobrovolný Jean-Marc Antoine Mariano Barriendos Dario Camuffo Mathias Deutsch Silvia Enzi Emanuela Guidoboni Oldřich Kotyza Fernando Sanchez Rodrigo 《Climatic change》1999,43(1):239-285
The severity and frequency of sixteenth-century floods of the Rhine, the Main, the middle and upper Elbe with its tributaries, rivers of northern and central Italy, the Garonne and rivers in Catalonia and Andalusia are analyzed using documentary evidence. The basic topographical and hydrological characteristics of the rivers investigated as well as the synoptic causes of their flooding during the instrumental period are presented. Different examples of modifications of the run-off process due to anthropogenic activity are discussed. Prevalence in flood occurrence during the second half of the sixteenth century in comparison to the first half is typical for central European and Andalusian rivers (mainly in the 1560s and 1590s) and agrees with the evolution of precipitation patterns. On the other hand, Italian and Catalonian rivers, in part, had a higher occurrence of floods during the first half of the century. Changes in the flooding seasons in both halves of the century are not unambiguous. Results of an analysis on a broader European scale show floods to be a random natural phenomena with limited areal extent defined by the spatial influence of forcing meteorological factors (continuous heavy rains, sudden melting of thick snow cover, etc.). Despite some limitations of documentary evidence, series of reconstructed historical floods are valuable sources of proxy data which can be utilized for the study of the flooding fluctuations in the pre-instrumental period. 相似文献
75.
Matthew Luck Niels Maumenee Diane Whited John Lucotch Samantha Chilcote Mark Lorang Daniel Goodman Kyle McDonald John Kimball Jack Stanford 《地球表面变化过程与地形》2010,35(11):1330-1343
Salmon populations are highly variable in both space and time. Accurate forecasting of the productivity of salmon stocks makes effective management and conservation of the resource extremely challenging. Furthermore, widespread and consistent data on the productivity of species‐specific and total salmon stocks in a river are almost nonexistent. Ranking rivers based on physical complexity derived from remote sensing allows rivers to be objectively compared. Our approach considered rivers with great geomorphic complexity (e.g. having expansive, multichanneled floodplains and/or on‐channel lakes) as likely to have greater productivity of salmon than rivers flowing in constrained or canyon‐bound channels. Our objective was to develop a database of landscape metrics that could be used to rank the rivers in relation to potential salmon productivity. We then examined the rankings in relation to existing empirical (monitoring) data describing productivity of salmon stocks. To extract the metrics for each river basin we used a digital elevation model and multispectral satellite imagery. We developed procedures to extract channel networks, floodplains, on‐channel lakes and other catchment features; variables such as catchment area, channel elevation, main channel length, floodplain area, and density of hydrojunctions (nodes) were measured. We processed 1509 catchments in the North Pacific Rim including the Kamchatka Peninsula in Russia and western North America. Overall, catchments were most physically complex in western Kamchatka and western Alaska, and particularly on the Arctic North Slope of Alaska. We could not directly examine coherence between potential and measured productivity except for a few rivers, but the expected relationship generally held. The resulting database and systematic ranking are objective tools that can be used to address questions about landscape structure and biological productivity at regional to continental extents, and provide a way to begin to efficiently prioritize the allocation of funding and resources towards salmon management and conservation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
76.
77.
Turbulent Structures in a Pine Forest with a Deep and Sparse Trunk Space: Stand and Edge Regions 总被引:1,自引:0,他引:1
Sylvain Dupont Mark R. Irvine Jean-Marc Bonnefond Eric Lamaud Yves Brunet 《Boundary-Layer Meteorology》2012,143(2):309-336
Forested landscapes often exhibit large spatial variability in vertical and horizontal foliage distributions. This variability
may affect canopy-atmosphere exchanges through its action on the development of turbulent structures. Here we investigate
in neutral stratification the turbulent structures encountered in a maritime pine forest characterized by a high, dense foliated
layer associated with a deep and sparse trunk space. Both stand and edge regions are considered. In situ measurements and
the results of large-eddy simulations are used and analyzed together. In stand conditions, far from the edge, canopy-top structures
appear strongly damped by the dense crown layer. Turbulent wind fluctuations within the trunk space, where the momentum flux
vanishes, are closely related to these canopy-top structures through pressure diffusion. Consequently, autocorrelation and
spectral analyses are not quite appropriate to characterize the vertical scale of coherent structures in this type of canopy,
as pressure diffusion enhances the actual scale of structures. At frequencies higher than those associated with canopy-top
structures, wind fluctuations related to wake structures developing behind tree stems are observed within the trunk space.
They manifest themselves in wind velocity spectra as secondary peaks in the inertial subrange region, confirming the hypothesis
of spectral short-cuts in vegetation canopies. In the edge region specific turbulent structures develop just below the crown
layer, in addition to canopy-top structures. They are generated by the wind shear induced by the sub-canopy wind jet that
forms at the edge. These structures provide a momentum exchange mechanism similar to that observed at the canopy top but in
the opposite direction and with a lower magnitude. They may develop as in plane mixing-layer flows, with some perturbations
induced by canopy-top structures. Wake structures are also observed within the trunk space in the edge region. 相似文献
78.
Anne Marie Treguier Claire Gourcuff Pascale Lherminier Herle Mercier Bernard Barnier Gurvan Madec Jean-Marc Molines Thierry Penduff Lars Czeschel Claus Böning 《Ocean Dynamics》2006,56(5-6):568-580
Numerical models are used to estimate the meridional overturning and transports along the paths of two hydrographic cruises,
carried out in 1997 and 2002 from Greenland to Portugal. We have examined the influence of the different paths of the two
cruises and found that it could explain 0.4 to 2 Sv of difference in overturning (the precise value is model-dependent). Models
show a decrease in the overturning circulation between 1997 and 2002, with different amplitudes. The CLIPPER ATL6 model reproduces
well the observed weakening of the overturning in density coordinates between the cruises; in the model, the change is due
to the combination of interannual and high-frequency forcing and internal variability associated with eddies and meanders.
Examination of the -coordinate overturning reveals model–data discrepancies: the vertical structure in the models does not change as much as
the observed one. The East Greenland current variability is mainly wind-forced in the ATL6 model, while fluctuations due to
eddies and instabilities explain a large part of the North Atlantic Current variability. The time-residual transport of dense
water and heat due to eddy correlations between currents and properties is small across this section, which is normal to the
direction of the main current. 相似文献
79.
Takuro Kobashi Jeffrey P. Severinghaus Jean-Marc Barnola Kenji Kawamura Tara Carter Tosiyuki Nakaegawa 《Climatic change》2010,100(3-4):733-756
Future Greenland temperature evolution will affect melting of the ice sheet and associated global sea-level change. Therefore, understanding Greenland temperature variability and its relation to global trends is critical. Here, we reconstruct the last 1,000 years of central Greenland surface temperature from isotopes of N2 and Ar in air bubbles in an ice core. This technique provides constraints on decadal to centennial temperature fluctuations. We found that northern hemisphere temperature and Greenland temperature changed synchronously at periods of ~20 years and 40–100 years. This quasi-periodic multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future. 相似文献
80.
This paper introduces an original method for climate change detection, called temporal optimal detection method. The method consists in searching for a smooth temporal pattern in the observations. This pattern can be either the response of the climate system to a specific forcing or to a combination of forcings. Many characteristics of this new method are different from those of the classical “optimal fingerprint” method. It allows to infer the spatial distribution of the detected signal, without providing any spatial guess pattern. The spatial properties of the internal climate variability doesn’t need to be estimated either. The estimation of such quantities being very challenging at regional scale, the proposed method is particularly well-suited for such scale. The efficiency of the method is illustrated by applying it on real homogenized datasets of temperatures and precipitation over France. A multimodel detection is performed in both cases, using an ensemble of atmosphere-ocean general circulation models for estimating the temporal patterns. Regarding temperatures, new results are highlighted, especially by showing that a change is detected even after removing the uniform part of the warming. The sensitivity of the method is discussed in this case, relatively to the computation of the temporal patterns and to the choice of the model. The method also allows to detect a climate change signal in precipitation. This change impacts the spatial distribution of the precipitation more than the mean over the domain. The ability of the method to provide an estimate of the spatial distribution of the change following the prescribed temporal patterns is also illustrated. 相似文献