Snow cover monitoring in the Northern Patagonia Icefield using MODIS satellite images (2000–2006)     

Paulina Lopez  Pascal Sirguey  Yves Arnaud  Bernard Pouyaud  Pierre Chevallier 《Global and Planetary Change》2008,61(3-4):103-116

The snow cover of the Northern Patagonia Icefield (NPI) was monitored after applying the Normalized Difference Snow Index (NDSI) and the Red/NIR band ratio to 134 Moderate Resolution Imaging Spectroradiometer (MODIS) images captured between 2000 and 2006. The final results show that the snow cover extent of the NPI fluctuates a lot in winter, in addition to its seasonal behaviour. The minimum snow cover extent of the period (3600 km²) was observed in March 2000 and the maximum (11,623 km²) in August 2001. We found that temperature accounts for approximately 76% of the variation of the snow cover extent over the entire icefield. We also show two different regimes of winter snow cover fluctuations corresponding to the eastern and the western sides of the icefield. The seasonality of the snow cover on the western side was determined by temperature rather than precipitation, while on the east side the seasonality of the snow cover was influenced by the seasonal behaviour of both temperature and precipitation. This difference can be explained by the two distinct climates: coastal and continental. The fluctuations in the winter snow cover extent were more pronounced and less controlled by temperature on the western side than on the eastern side of the icefield. Snow cover extent was correlated with temperature R² = 0.75 and R² = 0.74 for the western and eastern sides, respectively. Since limited meteorological data are available in this region, our investigation confirmed that the change in snow cover is an interesting climatic indicator over the NPI providing important insights in mass balance comprehension. Since snow and ice were distinguished snow cover fluctuations can be associated to fluctuations in the snow accumulation area of the NPI. In addition, days with minimum snow covers of summer season can be associated to the period in which Equilibrium Line Altitude (ELA) is the highest.  相似文献   

Thermal analysis of fractures at Cerberus Fossae, Mars: Detection of air convection in the porous debris apron     

R. Antoine  T. Lopez  M. Rabinowicz 《Icarus》2011,214(2):433-446

This study investigates the cause of high nighttime temperatures within Cerberus Fossae, a system of fractures affecting the Central Elysium Planitia. The inner parts (walls and floor) of the fractures are up to 40 K warmer than the surrounding plains. However, several temperature profiles exhibit a local temperature minima occurring in the central part of the fractures. We examined first the influence of cooling efficiency at night in the case of a strong reduction of the sky proportion induced by the fracture’s geometry. However, the lack of correlation between temperature and sky proportion, calculated from extracted Mars Orbiter Laser Altimeter (MOLA) profiles argues against this hypothesis. Albedo variations were considered but appear to be limited within the fractures, and are generally not correlated with the temperatures. Variations of the thermal properties of bedrocks exposures, debris aprons and sand dunes inferred from high-resolution images do not either correlate with temperature variations within the fractures. As none of these factors taken alone, or combined, can satisfactorily explain the temperature variations within and near the fracture, we suggest that geothermal heat transported by air convection within the porous debris aprons may contribute to explain high temperatures at night and the local minima on the fracture floor. The conditions for the occurrence of the suggested phenomenon and the consequences on the surface temperature are numerically explored. A conservative geothermal gradient of 20 mW/m² was used in the simulations, this value being consistent with either inferred lithosphere elastic thicknesses below the shield volcanoes of the Tharsis dome or values predicted from numerical simulations of the thermal evolution of Mars. The model results indicate that temperature differences of 10-20 K between the central and upper parts of the fracture are explained in the case of high Darcy velocities which require high permeability values (5 × 10⁻⁶ m²). The presence of coarse material composing the debris aprons may explain why this key criteria was met in the context of Cerberus Fossae.  相似文献   

Simulating the 1999 Capbreton canyon turbidity current with a Cellular Automata model     

T. Salles  T. Mulder  M. Gaudin  M.C. Cacas  S. Lopez  P. Cirac 《Geomorphology》2008,97(3-4):516-537

A numerical model has been developed for the simulation of turbidity currents driven by nonuniform, non cohesive sediment and flowing over a complex three dimensional submarine topography. The model is based on an alternative approach known as Cellular Automata paradigm. The model is validated by comparing a simulation with a reported field-scale event. The chosen case is a turbidity current which occurred in Capbreton Canyon and was initiated by a storm in December 1999. Using data from recent oceanographic cruises, the deposit of the event has been precisely described, which constrain values of model parameters. The model simulates the 1999 turbidity current over the actual canyon topography and related turbidite using three different types of particle. The model successfully simulates areas of erosion and deposition in the canyon. It predicts the vertical and longitudinal grain size evolution, and shows that the fining-up sequence can be deposited by several phases of deposition and erosion related to the current energetic variation during its evolution. This result could explain the presence of intrabed contacts or the frequent lack of facies in Bouma sequences.  相似文献   

Mapping of erosion rates in marly badlands based on a coupling of anatomical changes in exposed roots with slope maps derived from LiDAR data     

Jérôme Lopez Saez  Christophe Corona  Markus Stoffel  Georges Rovéra  Laurent Astrade  Frédéric Berger 《地球表面变化过程与地形》2011,36(9):1162-1171

Black marls form very extensive outcrops in the Alps and constitute some of the most eroded terrains, thus causing major problems of sedimentation in artificial storage systems (e.g. reservoirs) and river systems. In the experimental catchments near Draix (France), soil erosion rates have been measured in the past at the plot scale through a detailed monitoring of surface elevation changes and at the catchment scale through continuous monitoring of sediment yield in traps at basin outlets. More recently, erosion rates have been determined by means of dendrogeomorphic techniques in three monitored catchments of the Draix basin. A total of 48 exposed roots of Scots pine have been sampled and anatomical variations in annual growth rings resulting from denudation analysed. At the plot scale, average medium‐term soil erosion rates derived from exposed roots vary between 1·8 and 13·8 mm yr^?1 (average: 5·9 mm yr^?1) and values are significantly correlated with slope angle. The dendrogeomorphic record of point‐scale soil erosion rates matches very well with soil erosion rates measured in the Draix basins. Based on the point‐scale measurements and dendrogeomorphic results obtained at the point scale, a linear regression model involving slope angle was derived and coupled to high‐resolution slope maps obtained from a LiDAR‐generated digital elevation model so as to generate high‐resolution soil erosion maps. The resulting regression model is statistically significant and average soil erosion rates obtained from the areal erosion map (5·8, 5·2 and 6·2 mm yr^?1 for the Roubine, Moulin and Laval catchments, respectively) prove to be well in concert with average annual erosion rates measured in traps at the outlet of these catchments since 1985 (6·3, 4·1 and 6·4 mm yr^?1). This contribution demonstrates that dendrogeomorphic analyses of roots clearly have significant potential and that they are a powerful tool for the quantification and mapping of soil erosion rates in areas where measurements of past erosion is lacking. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Tectonic evolution of the Málaga Basin (Betic Cordillera). Regional implications     

Carlos Sanz De Galdeano  Angel Carlos Lopez Garrido 《Geodinamica Acta》2013,26(3):173-186

Abstract

During the Neogene (uppermost Aquitanian-Lower Burdigalian, Tortonian and Pliocene), three successive marine episodes took place in the present-day Malaga Basin. The first of these affected a wide area of the Belic Internal Zones and was brought to an abrupt conclusion by the westward displacement of these Zones, together with important horizontal movements associated with N70-100 direction strike-slip faults and the superposition of materials from the Campo de Gibraltar. The two other marine episodes were clearly controlled by vertical movements of NW-SE and NK-SW faults, caused by a clear E-W distension which, according to regional data, was associated with some compression in an approximately N-S direction. The area has also been affected, although to a lesser extent, by the uplift of the Betic Cordillera from the Upper Miocene to the present day.  相似文献   

Geochronology and geochemistry of Grenvillian igneous suites in the northern Oaxacan Complex, southern Mexico: tectonic implications   总被引：1，自引：0，他引：1  

J. Duncan Keppie  J. Dostal  K. L. Cameron  L. A. Solari  F. Ortega-Gutirrez  R. Lopez 《Precambrian Research》2003,120(3-4):365-389

Chemical and U–Pb isotopic analyses of metaigneous rocks in the northern Oaxacan Complex in southern Mexico indicate that they form part of two granitic–gabbroic suites intruded at 1157–1130 and 1012 Ma, which were metamorphosed under granulite facies conditions between 1004 and 980 Ma. Although the older suite has both within-plate and arc geochemical signatures, the arc characteristics (enrichment of La and Ce relative to Nb, Ta, and Th) are inferred to result from crustal contamination, a conclusion consistent with their negative _Nd signatures. The younger suite is spatially associated with anorthosites (from which we were unable to acquire a protolith age), suggesting that collectively it forms part of anorthosite–mangerite–charnockite–granite (AMCG) suites. The tholeiitic nature of the mafic rocks along with the within-plate character of the felsic rocks suggests that they were intruded during extension related to either farfield backarc rifting, rifting above a slab window, or anorogenic intercontinental rifting. Potentially correlative AMCG suites are widespread in Mexico, the Grenville Province of eastern Canada and northeastern USA, and the Andean massifs of Colombia, however, Pb isotopic data most closely resemble those in South America. These data are consistent with published hypotheses that suggest Oaxaquia represents an exotic terrane derived from Amazonia.  相似文献   

Sensitivity of the Northern Hemisphere circulation to North Atlantic SSTs in the ARPÈGE Climate AGCM     

P. Lopez  T. Schmith  E. Kaas 《Climate Dynamics》2000,16(7):535-547

In order to determine the response of the atmosphere to winter sea surface temperature (SST) anomalies in the North Atlantic area, we carried out ensemble runs of 20 years, forced with constant, perturbed, SST patterns using the climate version of the ARPèGE AGCM, at T42 resolution. A Monte Carlo technique was applied, in such a way that the control experiment, forced with observed climatological temperatures, and the four scenario experiments, forced with perturbed SSTs are equivalent to a length of 20 independent winters. Four anomalous winter North Atlantic sea surface temperature (SST) fields have been constructed by considering the observed SST variability in the main basins, namely the Labrador Sea and the Greenland Sea. Two patterns are of the `seesaw' type, while the two others have same the polarity in both basins. The patterns have been reinforced by a factor of 5–6 compared to presently observed multi-annual anomalies, in order to get SST anomalies which may have occurred during periods of the Little Ice Age. The differences between each of the four winter simulations with perturbed SSTs and the control run are analyzed in terms of tropospheric thickness, mean-sea-level pressure and storm activity. The `seesaw' type patterns give a weaker response in the tropospheric thickness fields than the two others. This is expected from simple considerations. In the mean circulation and synoptic activity, it appears that the Labrador Sea SST is important in determining the atmospheric response. This is probably due to enhanced temperature gradients east of New Foundland which enhances the storm activity. Received: 23 September 1998 / Accepted: 17 November 1999  相似文献   

Spatial coherency analysis of seismic ground motions from a rock site dense array implemented during the Kefalonia 2014 aftershock sequence          下载免费PDF全文

A. Svay  V. Perron  A. Imtiaz  I. Zentner  R. Cottereau  D. Clouteau  P.‐Y. Bard  F. Hollender  F. Lopez‐Caballero 《地震工程与结构动力学》2017,46(12):1895-1917

The objective of studies presented in this paper is to analyse the spatial incoherency of seismic ground motions using signals from a velocimeter dense array located on a rock site, recording the aftershock sequence of the two M6 Kefalonia earthquakes that occurred in January/February 2014 (Kefalonia island, Greece). The analyses are carried out with both horizontal and vertical components of velocigrams for small separation distances of stations (<100 m). The coherencies of seismic ground motions identified from strong motion windows are compared with those identified from coda parts of signals. It is realized that there is no significant difference between the coherencies estimated from those two parts of signals. The influence of earthquake event number on the result of coherencies and the dispersions of coherencies estimated from different earthquake events are presented. Finally, coherencies estimated from the dense array are compared with several coherency models proposed and widely used in the literature. The possibility of modifying some parameters of those existing coherency models to fit with in situ coherencies are discussed and presented. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Establishing habitat-specific indicator species in Tierra del Fuego with freshwater macroinvertebrates     

Christopher B. Anderson  Montana Johnson  María Eugenia Lopez 《新西兰海洋与淡水研究杂志》2018,52(1):145-154

As a tool to understand Tierra del Fuego’s basic ecology and detect changes due to human pressures, this study develops habitat bioindicators. We compared the freshwater benthic macroinvertebrates at 61 study sites in six habitat types: grassland streams, urbanised streams, forested streams, beaver ponds, lakes and peat bog ponds. Forty-nine taxa were identified; insects were the most diverse group. Beaver pond, lake and grassland stream assemblages were similar, as were those from lakes, grassland streams and peat bog ponds. Fourteen taxa were habitat-specific. In forests, these included mayfly scrapers (Andesiops, Meridialaris) and blackfly filterers (Gigantodax). In lakes, two copepod filterers were indicators, and in urban streams, one shredder (Aphroteniella) and three collector-gatherers (springtail, earthworm, aquatic worm). Predators (Corixa, Aeshna) were characteristic of peat bog ponds. Beaver ponds had no indicator species. Establishing links between species and ecosystems constitutes the beginning of a broader effort to understand anthropogenic impacts to Fuegian watersheds.  相似文献   

Two-Component Structure of the Radio Source 0014+813 from VLBI Observations within the CONT14 Program     

O. A. Titov  Yu. R. Lopez 《Astronomy Letters》2018,44(3):139-148

We consider a method of reconstructing the structure delay of extended radio sources without constructing their radio images. The residuals derived after the adjustment of geodetic VLBI observations are used for this purpose. We show that the simplest model of a radio source consisting of two point components can be represented by four parameters (the angular separation of the components, the mutual orientation relative to the poleward direction, the flux-density ratio, and the spectral index difference) that are determined for each baseline of a multi-baseline VLBI network. The efficiency of this approach is demonstrated by estimating the coordinates of the radio source 0014+813 observed during the two-week CONT14 program organized by the International VLBI Service (IVS) in May 2014. Large systematic deviations have been detected in the residuals of the observations for the radio source 0014+813. The averaged characteristics of the radio structure of 0014+813 at a frequency of 8.4 GHz can be calculated from these deviations. Our modeling using four parameters has confirmed that the source consists of two components at an angular separation of ~0.5 mas in the north–south direction. Using the structure delay when adjusting the CONT14 observations leads to a correction of the average declination estimate for the radio source 0014+813 by 0.070 mas.  相似文献