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641.
The objective of this study was to examine the streamflow variability of Argentinean Andean basins (22°–52°S). Trends and step changes of seven hydrological variables were analysed. In addition, relationships between the hydrological variables and Pacific Decadal Oscillation (PDO), Niño 3.4, and Southern Annular Mode (SAM) indices were analysed. Most streamflow variables showed upward trends in the northwest and central-western basins, while downward trends were identified in the Patagonia (southwestern) region. Streamflow of the central-western and Patagonian basins was positively correlated with the Niño 3.4 index. Moreover, an inverse relationship with the SAM was found in watersheds south of 37°S. Positive step changes associated with the PDO phases in the north and central-western basins in the mid-1970s were detected, while negative step changes resulted in Patagonia between 1970 and 2000. This research provides new evidence of the influence of major climate modes on streamflow variability in the western rivers of Argentina. 相似文献
642.
Simona Ghizzardi Martino Marelli David Salvetti Fabio Gastaldello Silvano Molendi Andrea De Luca Alberto Moretti Mariachiara Rossetti Andrea Tiengo 《Experimental Astronomy》2017,44(3):273-285
A detailed characterization of the particle induced background is fundamental for many of the scientific objectives of the Athena X-ray telescope, thus an adequate knowledge of the background that will be encountered by Athena is desirable. Current X-ray telescopes have shown that the intensity of the particle induced background can be highly variable. Different regions of the magnetosphere can have very different environmental conditions, which can, in principle, differently affect the particle induced background detected by the instruments. We present results concerning the influence of the magnetospheric environment on the background detected by EPIC instrument onboard XMM-Newton through the estimate of the variation of the in-Field-of-View background excess along the XMM-Newton orbit. An important contribution to the XMM background, which may affect the Athena background as well, comes from soft proton flares. Along with the flaring component a low-intensity component is also present. We find that both show modest variations in the different magnetozones and that the soft proton component shows a strong trend with the distance from Earth. 相似文献
643.
Victor Quintino Franca Sangiorgio Fernando Ricardo Renato Mamede Adília Pires Rosa Freitas Ana Maria Rodrigues Alberto Basset 《Estuarine, Coastal and Shelf Science》2009
An experimental study on Phragmites australis leaf litter decomposition was conducted in the estuarine environment, Ria de Aveiro, Western Portugal, using the leaf-bag technique, with fine- (1 mm) and coarse-mesh (5 mm) bags. The leaf bags were placed in the field sites at day 0, covering a complete salinity gradient, and replicates were collected over time, at days 3 (leaching), 7, 15, 30 and 60. The biomass loss through the leaching phase, about 20% of the initial leaf mass, was independent of both the salinity and the bag mesh size. The biomass decay pattern along the salinity gradient varied through time and presented strong similarities between the two mesh sizes, with the remaining biomass always lower in the 5 mm mesh-size bags. At days 7 and 15, the lowest remaining biomass was observed at the head of the estuary, the preferential distribution area of P. australis. At day 30, the remaining biomass was higher in the marine area and diminished under a direct relationship with salinity, reaching the lowest value in the freshwater environment, with values ranging from 66% to 44% of the initial weight in 5 mm bags, and from 79% to 51% in 1 mm bags. The largest heterogeneity in the remaining biomass among the study areas positioned along the salinity gradient was found close to days 30 (5 mm) and 40 (1 mm). The overall results indicate that the relationship between leaf decay rate and salinity depends on the decay time considered (k15, k30 or k60) and, for the later stages (k60), also on the leaf-bag mesh size. This implies that the use of leaf litter decay rates as a functional indicator in transitional waters will need to take into consideration the factor location in the salinity gradient and leaf litter stage at which the decay rate is determined. The differences between the decay rates with the mesh size acted mainly at the level of the absolute k value and not at the level of the pattern along the salinity gradient. Even so, the data obtained at the mouth of the estuary, in the area closest to a fully marine environment, indicated that after the initial biomass loss through leaching, P. australis decayed either very slowly, in the 5 mm, or not at all, in the 1 mm mesh bags. 相似文献
644.
Carlos Alberto Galaz-Samaniego M. Cristina Peñalba Francisco Abraham Paz-Moreno Iván Rosario Espinoza-Encinas Kinardo Flores-Castro Rogelio Monreal Carlos Lizárraga-Celaya 《第四纪科学杂志》2023,38(1):76-91
During the last glacial termination, the climate system experienced intense global variations whose causes and impacts are not fully defined, particularly for low latitudes. The northwestern Mexico Sky Islands present a climate-sensitive ideal setting to record palaeoecological and palaeoclimatic changes due to their physiographic complexity and location in the ecotone between temperate and tropical ecosystems. High-resolution pollen analysis and a detailed sedimentological study were conducted at the Ciénega Tonibabi tropical thorn scrub site. The 15 540–0 cal a bp nearly continuous record shows that the North Atlantic Ocean did have a cold and humid climatic influence during the glacial stages of the end of the Pleistocene, including a sharp pulse during the Younger Dryas. However, a shift to the Pacific Ocean influence occurred during the Holocene, which led to the development of the El Niño conditions prevailing today. Colder and warmer phases follow one another with higher or lower winter precipitation, including a sharp Bølling–Allerød and development and intensification of the North American monsoon. They are reflected in hydrological changes as well as in the advances, retreats and intermingling of coniferous forests and tropical thorn scrub. 相似文献