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71.
We analyze the observations of a quiescent prominence acquired by the Téléscope Heliographique pour l’Étude du Magnetisme et des Instabilités Solaires (THEMIS) in the He?i 5876 Å (He?i D3) multiplet aiming to measure the spectral characteristics of the He?i D3 profiles and to find for them an adequate fitting model. The component characteristics of the He?i D3 Stokes I profiles are measured by the fitting system by approximating them with a double Gaussian. This model yields an He?i D3 component peak intensity ratio of \(5.5\pm0.4\), which differs from the value of 8 expected in the optically thin limit. Most of the measured Doppler velocities lie in the interval ±?5 km?s?1, with a standard deviation of ±?1.7 km?s?1 around the peak value of 0.4 km?s?1. The wide distribution of the full-width at half maximum has two maxima at 0.25 Å and 0.30 Å for the He?i D3 blue component and two maxima at 0.22 Å and 0.31 Å for the red component. The width ratio of the components is \(1.04\pm0.18\). We show that the double-Gaussian model systematically underestimates the blue wing intensities. To solve this problem, we invoke a two-temperature multi-Gaussian model, consisting of two double-Gaussians, which provides a better representation of He?i D3 that is free of the wing intensity deficit. This model suggests temperatures of 11.5 kK and 91 kK, respectively, for the cool and the hot component of the target prominence. The cool and hot components of a typical He?i D3 profile have component peak intensity ratios of 6.6 and 8, implying a prominence geometrical width of 17 Mm and an optical thickness of 0.3 for the cool component, while the optical thickness of the hot component is negligible. These prominence parameters seem to be realistic, suggesting the physical adequacy of the multi-Gaussian model with important implications for interpreting He?i D3 spectropolarimetry by current inversion codes. 相似文献
72.
Mario González-Escobar Francisco Suárez-Vidal José Antonio Hernández-Pérez Arturo Martín-Barajas 《Geo-Marine Letters》2010,30(6):575-584
This study examines the structural characteristics of the northern Gulf of California by processing and interpreting ca. 415 km of two-dimensional multi-channel seismic reflection lines (data property of Petróleos Mexicanos PEMEX) collected in the vicinity of the border between the Wagner and Consag basins. The two basins appear to be a link between the Delfín Superior Basin to the south, and the Cerro Prieto Basin to the north in the Mexicali-Imperial Valley along the Pacific–North America plate boundary. The seismic data are consistent with existing knowledge of four main structures (master faults) in the region, i.e., the Percebo, Santa María, Consag Sur, and Wagner Sur faults. The Wagner and Consag basins are delimited to the east by the Wagner Sur Fault, and to the west by the Consag Sur Fault. The Percebo Fault borders the western margin of the modern Wagner Basin depocenter, and is oriented N10°W, dipping (on average) ~40° to the northeast. The trace of the Santa María Fault located in the Wagner Basin strikes N19°W, dipping ~40° to the west. The Consag Sur Fault is oriented N14°W, and dips ~42° to the east over a distance of 21 km. To the east of the study area, the Wagner Sur Fault almost parallels the Consag Sur Fault over a distance of ~86 km, and is oriented N10°W with an average dip of 59° to the east. Moreover, the data provide new evidence that the Wagner Fault is discontinuous between the two basins, and that its structure is more complex than previously reported. A structural high separates the northern Consag Basin from the southern Wagner Basin, comprising several secondary faults oriented NE oblique to the main faults of N–S direction. These could represent a zone of accommodation, or transfer zone, where extension could be transferred from the Wagner to the Consag Basin, or vice versa. This area shows no acoustic basement and/or intrusive body, which is consistent with existing gravimetric and magnetic data for the region. 相似文献
73.
74.
Land cover change and carbon stores in a tropical montane cloud forest in the Sierra Madre Oriental,Mexico 总被引:1,自引:0,他引:1
Edgar G.LEIJA-LOREDO Numa P.PAVóN Arturo SáNCHEZ-GONZáLEZ Rodrigo RODRIGUEZ-LAGUNA Gregorio áNGELES-PéREZ 《山地科学学报》2018,15(10):2136-2147
Tropical montane cloud forest is one of the ecosystems with the highest biomass worldwide, representing an important carbon store. Globally its deforestation index is –1.1%, but in Mexico it is higher than –3%. Carbon estimates are scarce globally, particularly in Mexico. The objective of this study was to simulate future land-cover scenarios for the Sierra Madre Oriental in Mexico, by analyzing past forest cover changes. Another objective was to estimate stored carbon in the two study areas. These objectives involve the generation of information that could be useful inputs to anti-deforestation public policy such as the REDD+ strategy. Remote sensing was used to measure land cover change and estimate carbon stocks. Satellite images from 2015, 2000 and 1986 were used, and Dinamica EGO freeware generatedmodels of future projections. Between 1986 and 2015, 5171 ha of forest were converted to pasture. The annual deforestation rates were –1.5% for Tlanchinol and –1.3% for the San Bartolo Tutotepec sites. Distance to roads and marginalization were highly correlated with deforestation. By 2030, an estimated 3608 ha of forest in these sites will have been converted to pasture. Stored carbon was estimated at 16.35 Mg C ha-1 for the Tlanchinol site and 12.7 Mg C ha-1 for the San Bartolo site. In the Sierra Madre Oriental deforestation due to land cover change(–1.4%) is higher than levels reported worldwide. Besides having high values of stored carbon(14.5 Mg C ha-1), these forests have high biodiversity. The models' outputs show that the deforestation process will continue if action is not taken to avoid the expansion of livestock pasturing. This can be done by paying incentives for forest conservation to the owners of the land. The results suggest that REDD+ is currently the most viable strategy for reducing deforestation rates in tropical montane cloud forests in Sierra Madre Oriental. 相似文献
75.
Lithologic controls on mineralization at the Lagunas Norte high-sulfidation epithermal gold deposit, northern Peru 总被引:1,自引:0,他引:1
Luis M. Cerpa Thomas Bissig Kurt Kyser Craig McEwan Arturo Macassi Hugo W. Rios 《Mineralium Deposita》2013,48(5):653-673
The 13.1-Moz high-sulfidation epithermal gold deposit of Lagunas Norte, Alto Chicama District, northern Peru, is hosted in weakly metamorphosed quartzites of the Upper Jurassic to Lower Cretaceous Chimú Formation and in overlying Miocene volcanic rocks of dacitic to rhyolitic composition. The Dafne and Josefa diatremes crosscut the quartzites and are interpreted to be sources of the pyroclastic volcanic rocks. Hydrothermal activity was centered on the diatremes and four hydrothermal stages have been defined, three of which introduced Au ± Ag mineralization. The first hydrothermal stage is restricted to the quartzites of the Chimú Formation and is characterized by silice parda, a tan-colored aggregate of quartz-auriferous pyrite–rutile ± digenite infilling fractures and faults, partially replacing silty beds and forming cement of small hydraulic breccia bodies. The δ34S values for pyrite (1.7–2.2?‰) and digenite (2.1?‰) indicate a magmatic source for the sulfur. The second hydrothermal stage resulted in the emplacement of diatremes and the related volcanic rocks. The Dafne diatreme features a relatively impermeable core dominated by milled slate from the Chicama Formation, whereas the Josefa diatreme only contains Chimú Formation quartzite clasts. The third hydrothermal stage introduced the bulk of the mineralization and affected the volcanic rocks, the diatremes, and the Chimú Formation. In the volcanic rocks, classic high-sulfidation epithermal alteration zonation exhibiting vuggy quartz surrounded by a quartz–alunite and a quartz–alunite–kaolinite zone is observed. Company data suggest that gold is present in solid solution or micro inclusions in pyrite. In the quartzite, the alteration is subtle and is manifested by the presence of pyrophyllite or kaolinite in the silty beds, the former resulting from relatively high silica activities in the fluid. In the quartzite, gold mineralization is hosted in a fracture network filled with coarse alunite, auriferous pyrite, and enargite. Alteration and mineralization in the breccias were controlled by permeability, which depends on the type and composition of the matrix, cement, and clast abundance. Coarse alunite from the main mineralization stage in textural equilibrium with pyrite and enargite has δ34S values of 24.8–29.4?‰ and $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ values of 6.8–13.9?‰, consistent with H2S as the dominant sulfur species in the mostly magmatic fluid and constraining the fluid composition to low pH (0–2) and logfO2 of ?28 to ?30. Alunite–pyrite sulfur isotope thermometry records temperatures of 190–260 °C; the highest temperatures corresponding to samples from near the diatremes. Alunite of the third hydrothermal stage has been dated by 40Ar/39Ar at 17.0?±?0.22 Ma. The fourth hydrothermal stage introduced only modest amounts of gold and is characterized by the presence of massive alunite–pyrite in fractures, whereas barite, drusy quartz, and native sulfur were deposited in the volcanic rocks. The $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ values of stage IV alunite vary between 11.5 and 11.7?‰ and indicate that the fluid was magmatic, an interpretation also supported by the isotopic composition of barite (δ34S?=?27.1 to 33.8?‰ and $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ ?=?8.1 to 12.7?‰). The Δ34Spy–alu isotope thermometry records temperatures of 210 to 280 °C with the highest values concentrated around the Josefa diatreme. The Lagunas Norte deposit was oxidized to a depth of about 80 m below the current surface making exploitation by heap leach methods viable. 相似文献
76.
Qinglong You Arturo Sanchez-Lorenzo Martin Wild Doris Folini Klaus Fraedrich Guoyu Ren Shichang Kang 《Climate Dynamics》2013,40(7-8):2073-2086
In this study, the annual and seasonal variations of all-sky and clear-sky surface solar radiation (SSR) in the eastern and central Tibetan Plateau (TP) during the period 1960–2009 are investigated, based on surface observational data, reanalyses and ensemble simulations with the global climate model ECHAM5-HAM. The mean annual all-sky SSR series shows a decreasing trend with a rate of ?1.00 Wm?2 decade?1, which is mainly seen in autumn and secondly in summer and winter. A stronger decrease of ?2.80 Wm?2 decade?1 is found in the mean annual clear-sky SSR series, especially during winter and autumn. Overall, these results confirm a tendency towards a decrease of SSR in the TP during the last five decades. The comparisons with reanalysis show that both NCEP/NCAR and ERA-40 reanalyses do not capture the decadal variations of the all-sky and clear-sky SSR. This is probably due to a missing consideration of aerosols in the reanalysis assimilation model. The SSR simulated with the ECHAM5-HAM global climate model under both all-sky and clear-sky conditions reproduce the decrease seen in the surface observations, especially after 1980. The steadily increasing aerosol optical depth (AOD) at 550 nm over the TP in the ECHAM5-HAM results suggests transient aerosol emissions as a plausible cause. 相似文献
77.
Agustín Gómez-Alvarez Diana Meza-Figueroa Arturo I. Villalba-Atondo Jesús Leobardo Valenzuela-García Jorge Ramírez-Hernández Javier Almendariz-Tapia 《Environmental Geology》2009,57(7):1469-1479
The San Pedro River (SPR) is located in northern Sonora (Mexico) and southeastern Arizona (USA). SPR is a transboundary river
that develops along the Sonora (Mexico) and Arizona (USA) border, and is considered the main source of water for a variety
of users (human settlements, agriculture, livestock, and industry). The SPR originates in the historic Cananea mining area,
which hosts some of the most important copper mineralizations in Mexico. Acid mine drainage derived from mine tailings is
currently reaching a tributary of the SPR near Cananea City, resulting in the contamination of the SPR with heavy metals and
sulfates in water and sediments. This study documents the accumulation and distribution of heavy metals in surface water along
a segment of the SPR from 1993 to 2005. Total concentrations of Cd, Cu, Fe, Mn, Pb, and Zn in surface waters are above maximum
permissible levels in sampling sites near mine tailing deposits. Nevertheless, a significant decrease in the Fe and SO4
2− in surface water (SO4
2−: 7,180–460.39 mg/L; Fe: 1,600–9.51 mg/L) as well as a gradual decrease in the heavy and transition metal content were observed
during the period from 1994 to 2005. Approximately 2.3 km downstream of the mine tailings, the heavy metal content of the
water drops quickly following an increase in pH values due to the discharging of wastewater into the river. The attenuation
of the heavy metal content in surface waters is related to stream sediment precipitation (accompanied by metal coprecipitation
and sorption) and water dilution. Determining the heavy metal concentration led to the conclusion that the Cananea mining
area and the San Pedro River are ecosystems that are impacted by the mining industry and by untreated wastewater discharges
arising from the city of Cananea (Sonora, Mexico). 相似文献
78.
Arturo Sousa Pablo García-Murillo Sükran Sahin Julia Morales Leoncio García-Barrón 《Climatic change》2010,100(3-4):525-557
Recent studies have shown the value of place names as environmental indicators. Until now they have not been applied to the effects of climate change, because verifying such relationship by this approach requires a multidisciplinary analysis and a study area where the anthropic impact has been recent. This study aims to test the possibility in a study area little altered by man until the second half of the twentieth century (Doñana Natural Park, SW Spain), and with a heritage very rich in wetlands. The results show that the desiccation of these wetlands is reflected in the local toponymy, and that in turn this regression is related with the end of the Little Ice Age and with the beginning of warming in southern Europe during the twentieth century. The coincidence of these results with data published for Arctic latitudes reveals—in our opinion—the possibility that certain place names can be used as indicators of recent climate changes, at least in some ecosystems. 相似文献
79.
Leoncio García-Barrón Julia Morales Arturo Sousa 《Theoretical and Applied Climatology》2013,114(3-4):445-457
Variability in precipitation affects annual total records and causes instability in rainfall distribution throughout the year. Our aim in this study was to develop a procedure, based on pluviometric centralisation and dispersion parameters, that is able to characterise rainfall distribution throughout a year of precipitation in a unique, condensed and precise manner. This enabled the evolution of intra-annual precipitation from 1837 to 2010 in the southwest of the Iberian Peninsula to be determined. The obtained results showed irregular oscillations of the parameters during the selected period. Specifically, patterns of precipitation in recent decades revealed the following differentiating features: the displacement of the most intense rainy periods in autumn with a consequent decrease in precipitation in spring, and more erratic distribution throughout the year with an increase of the frequency of intra-annual dispersion peaks. 相似文献
80.
The paper reviews a number of challenges associated with reducing degradation and its related emissions through national approaches
to REDD+ under UNFCCC policy. It proposes that in many countries, it may in the short run be easier to deal with the kinds
of degradation that result from locally driven community over-exploitation of forest for livelihoods, than from selective
logging or fire control. Such degradation is low-level, but chronic, and is experienced over very large forest areas. Community
forest management programmes tend to result not only in reduced degradation, but also in forest enhancement; moreover they
are often popular, and do not require major political shifts. In principle these approaches therefore offer a quick start
option for REDD+. Developing reference emissions levels for low-level locally driven degradation is difficult however given
that stock losses and gains are too small to be identified and measured using remote sensing, and that in most countries there
is little or no forest inventory data available. We therefore propose that forest management initiatives at the local level,
such as those promoted by community forest management programmes, should monitor, and be credited for, only the net increase
in carbon stock over the implementation period, as assessed by ground level surveys at the start and end of the period. This
would also resolve the problem of nesting (ensuring that all credits are accounted for against the national reference emission
level), since communities and others at the local level would be rewarded only for increased sequestration, while the national
reference emission level would deal only with reductions in emissions from deforestation and degradation. 相似文献