Spatial patterns and temporal trends of precipitation in Iran   总被引：3，自引：0，他引：3  

Tayeb Raziei  Jamal Daryabari  Isabella Bordi  Luis S. Pereira 《Theoretical and Applied Climatology》2014,115(3-4):531-540

Spatial patterns of monthly, seasonal and annual precipitation over Iran and the corresponding long-term trends for the period 1951–2009 are investigated using the Global Precipitation Climatology Centre gridded dataset. Results suggest that the spatial patterns of annual, winter and spring precipitation and the associated coefficients of variation reflect the role of orography and latitudinal extent between central-southern arid and semi-arid regions and northern and western mountainous areas. It is also shown that precipitation occurrence is almost regularly distributed within the year in northern areas while it is more concentrated in a few months in southern Iran. The spatial distribution of Mann–Kendal trend test (Z statistics) for annual precipitation showed downward trend in north-western and south-eastern Iran, whereas western, central and north-eastern exhibited upward trend, though not statistically significant in most regions. Results for winter and autumn revealed upward trend in most parts of the country, with the exception of north-western and south-eastern where a downward trend is observed; in spring and summer, a downward trend seems to prevail in most of Iran. However, for all seasons the areas where the detected trend is statistically significant are limited to a few spot regions. The overall results suggest that the precipitation is decreasing in spring and summer and increasing in autumn and winter in most of Iran, i.e. less precipitation during the warm season with a consequent intensification of seasonality and dryness of the country. However, since the detected trends are often not statistically significant, any stringent conclusion cannot be done on the future tendencies.  相似文献   

Recharge of aquifers by flood events in an arid region     

Isabella Shentsis  Eliyahu Rosenthal 《水文研究》2003,17(4):695-712

The process of aquifer recharge by flood events in an arid region was investigated as applied to the Hazeva Formation (the Karkom graben, the Wadi Paran watershed, Israel). The hydrological model was established as a complex system, with due regard for groundwater and transmission losses of surface runoff. It was based on a previously outlined hydrogeological model of the Karkom graben and a model of transmission losses in arid watercourses under conditions of data deficiency. Proceeding from calculation of groundwater balances, the contribution of surface runoff as a decisive balance component was confirmed. The main characteristics of aquifer regimes, such as changes in storage volume and groundwater level, as well as lateral flow, were all found to be dependent upon the net extraction rate, i.e. pumpage discounting replenishment by flood events. Analysis and physical interpretation of model parameters enabled assessment of the influence of groundwater extraction on aquifer recharge. This became apparent as increasing absorption capacity and recharge availability of the aquifer as a result of the groundwater abstraction. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Multiple precursors of secondary mineralogical assemblages in CM chondrites          下载免费PDF全文

Isabella Pignatelli  Yves Marrocchi  Lionel. G. Vacher  Rémi Delon  Matthieu Gounelle 《Meteoritics & planetary science》2016,51(4):785-805

We report a petrographic and mineralogical survey of tochilinite/cronstedtite intergrowths (TCIs) in Paris, a new CM chondrite considered to be the least altered CM identified to date. Our results indicate that type‐I TCIs consist of compact tochilinite/cronstedtite rims surrounding Fe‐Ni metal beads, thus confirming kamacite as the precursor of type‐I TCIs. In contrast, type‐II TCIs are characterized by complex compositional zoning composed of three different Fe‐bearing secondary minerals: from the outside inwards, tochilinite, cronstedtite, and amakinite. Type‐II TCIs present well‐developed faces that allow a detailed morphological analysis to be performed in order to identify the precursors. The results demonstrate that type‐II TCIs formed by pseudomorphism of the anhydrous silicates, olivine, and pyroxene. Hence, there is no apparent genetic relationship between type‐I and type‐II TCIs. In addition, the complex chemical zoning observed within type‐II TCIs suggests that the alteration conditions evolved dramatically over time. At least three stages of alteration can be proposed, characterized by alteration fluids with varying compositions (1) Fe‐ and S‐rich fluids; (2) S‐poor and Fe‐ and Si‐rich fluids; and (3) S‐ and Si‐poor, Fe‐rich fluids. The presence of unaltered silicates in close association with euhedral type‐II TCIs suggests the existence of microenvironments during the first alteration stages of CM chondrites. In addition, the absence of Mg‐bearing secondary minerals in Paris TCIs suggests that the Mg content increases during the course of alteration.  相似文献   

Crystal recycling in the steady-state system of the active Stromboli volcano: a 2.5-ka story inferred from in situ Sr-isotope and trace element data     

Lorella Francalanci  Riccardo Avanzinelli  Isabella Nardini  Massimo Tiepolo  Jon P. Davidson  Riccardo Vannucci 《Contributions to Mineralogy and Petrology》2012,163(1):109-131

In situ Sr-isotope data by microdrilling, coupled with major and trace element analyses, have been performed on plagioclase and clinopyroxene from seven samples collected during the 2002–2003 eruptive crisis at Stromboli volcano (Aeolian Islands, Italy). On 28 December 2002, the persistent moderate explosive activity was broken by an effusive event lasting about 7 months. A more violent explosion (paroxysm) occurred on 5 April 2003. Two magma types were erupted, namely a volatile-poor and highly porphyritic magma (HP-magma) poured out as scoria or lava and a volatile-rich, phenocryst-poor magma (LP-magma) found as pumice. LP-magma differs from the HP-magma also for its slightly less-evolved chemistry, the groundmass composition and the lower Sr-isotope ratios. Micro-Sr-isotope data show the presence of zoned minerals in strong isotope disequilibrium, as previously found in products erupted in 1984, 1985 and 1996 AD, with ⁸⁷Sr/⁸⁶Sr values generally decreasing from cores to rims of minerals. Only some outer rims testify for equilibrium with the host groundmass. The internal mineral zones with high Sr-isotope ratios (0.70665–0.70618) are interpreted as ‘antecrysts’, crystallised during the previous activity and recycled in the present-day system since the opening shoshonitic activity of the Recent Period, which occurred at about 2.5 ka ago. This result has implications for the dynamics of the present-day plumbing system of Stromboli at intermediate pressure (about 2–3 km depth) and allows us to propose a model whereby an HP-magma reservoir is directly interconnected at the bottom with a cumulate crystal much reservoir. Efficient mixing between residing HP- and input LP-magmas can occur in this reservoir, due to more similar rheological characteristics of the two magmas than in the conduit, where crystallisation is enhanced by degassing. Antecrysts (and possibly melts) re-enter in the HP-magma reservoir both from the bottom, recycled by ascending LP-magmas crossing the crystal mush, and from the top, recycled by descending degassed and dense HP-magma, residual of the periodic Strombolian explosions at the surface. The isotope variation measured in the groundmasses allows calculating the proportion of the LP-magma entering the shallow HP-magma reservoir at ~20%. From this proportion, we estimate that the total volume of LP-magma input during 2002–2003 closely matches the magma volume erupted in the effusive event, suggesting a steady-state system at broadly constant volume. The comparison with estimates of the LP-magma volume ejected by the paroxysm indicates that the LP-magma amount directly reaching the surface during the 5 April paroxysm is minimal with respect to that entering the system.  相似文献   

Transient response to well-mixed greenhouse gas changes     

Isabella Bordi  Klaus Fraedrich  Alfonso Sutera  Xiuhua Zhu 《Theoretical and Applied Climatology》2012,109(1-2):245-252

A change in CO₂ concentration induces a direct radiative forcing that modifies the planetary thermodynamic state, and hence the surface temperature. The infrared cooling, by assuming a constant temperature lapse-rate during the process, will be related to the surface temperature through the Stefan–Boltzmann law in a ratio proportional to the new infrared opacity. Other indirect effects, such as the water vapor and ice-albedo feedbacks, may amplify the system response. In the present paper, we address the question of how a global climate model with a mixed layer ocean responds to different rates of change of a well-mixed greenhouse gas such as CO₂. We provide evidence that different rates of CO₂ variation may lead to similar transient climates characterized by the same global mean surface temperature but different values of CO₂ concentration. Moreover, it is shown that, far from the bifurcation points, the model’s climate depends on the history of the radiative forcing displaying a hysteresis cycle that is neither static nor dynamical, but is related to the memory response of the model. Results are supported by the solutions of a zero-dimensional energy balance model.  相似文献   

On the feedback between water turbidity and microphytobenthos growth in shallow tidal environments     

Mattia Pivato  Luca Carniello  Isabella Moro  Paolo D'Odorico 《地球表面变化过程与地形》2019,44(5):1192-1206

Shallow tidal environments (e.g. bays, estuaries, lagoons) represent one of the most productive ecosystems in the world, and they are threatened by current climate change and increasing human pressure. Monitoring the bio-morphodynamic evolution of these environments is therefore a crucial task that requires a detailed and holistic scrutiny. The present study aims to investigate the temperature of the water–sediment continuum, its effect on the related microphytobenthos (MPB) growth and the related bio-stabilization of the bed sediment surface under different water depth and water turbidity conditions. We investigated the vertical energy transfer and the temperature dynamics by applying a 1-D model to a shallow coastal lagoon. Our results show that the water temperature does not substantially change under different turbidity conditions, whereas the sediment temperature exhibits important changes. Two major factors driving the MPB photosynthetic growth are the sediment surface temperature and the light availability at the sediment bed, which can both be computed using the vertical energy transfer model. We observed that, in general, clear water conditions better promote MPB growth over the entire year. The limiting factor for the photosynthetic process is usually the light availability at the bottom, which increases under clear water conditions. As MPB provides a bio-stabilizing effect on the bed sediments by producing a biofilm on the sediment surface that reduces sediment resuspension, our results suggest a positive feedback between MPB growth and water column turbidity. Furthermore, MPB growth and the related sediment bio-stabilization are clearly affected by the seasonal variation of surface sediment temperature and light availability. This seasonal variation of MPB growth rate and surface sediment bio-stabilization must be considered when studying the long-term morphodynamic evolution of tidal environments. © 2018 John Wiley & Sons Ltd.  相似文献   

Hydraulic zonation of the lagoons of Marano and Grado,Italy. A modelling approach     

Christian Ferrarin  Georg Umgiesser  Marco Bajo  Debora Bellafiore  Francesca De Pascalis  Michol Ghezzo  Giorgio Mattassi  Isabella Scroccaro 《Estuarine, Coastal and Shelf Science》2010

The hydraulic regime-based zonation scheme of the Lagoons of Marano and Grado (Italy) has been derived by means of numerical models. A finite element modelling system has been used to describe the water circulation taking in account different forces such as tide, wind and rivers. The model has been validated by comparing the simulation results against measured water levels, salinity and water temperature data collected in several stations inside the lagoons. The analysis of water circulation, salinity and spatial distribution of passive tracers released at the inlets, led to a physically-based division of the lagoons system into six subbasins. The derived classification scheme is of crucial value for understanding the renewal capacity and pollutants distribution patterns in the lagoon.  相似文献   

Migration of geothermal fluids in extensional terrains: the ore deposits of the Boccheggiano-Montieri area (southern Tuscany, Italy)     

Domenico Liotta  Giovanni Ruggieri  Andrea Brogi  Paolo Fulignati  Andrea Dini  Isabella Nardini 《International Journal of Earth Sciences》2010,99(3):623-644

An integrated study based on fluid inclusion, δ¹⁸O composition and structural analyses was carried out on a Pliocene fossil hydrothermal system, located to the South of the present active Larderello geothermal field, in the Boccheggiano-Montieri area. The study area is typified by mineralized cataclastic levels related to Late Oligocene–Early Miocene thrust surfaces, and to the following two generations of normal faults of Miocene and Pliocene ages, respectively. Within the damage zone of the Pliocene Boccheggiano fault, the mineralization is mainly made up of quartz and pyrite. Quartz + Pb–Zn sulfides, or quartz + Pb–Zn sulfides + fluorite + carbonates assemblages occur instead in the older cataclastic levels. Two generations of liquid-rich fluid inclusions were recognized in quartz and fluorite: the first one, with homogenization temperatures ranging between 172 and 331°C and salinity between 0.0 and 8.8 wt.% NaCl_equiv., records the early stage of hydrothermal activity. The second generation of fluid inclusions documents a later stage, with homogenization temperature from 124 to 288°C and salinity from 0.2 to 1.9 wt.% NaCl_equiv.. Fluid inclusions analyses also indicate that mixing of fluid with distinct salinities and/or temperatures was a widespread process during the early stage, and that fluid temperatures decreased moving from the Boccheggiano fault toward the more distal and older cataclastic levels. The δ¹⁸O values of water in equilibrium with hydrothermal quartz, which range from −5.7 to −0.1‰, are related to the circulation of meteoric water mixed with saline water that leached the evaporite level and enriched in δ¹⁸O through water–rock interaction, and/or with magmatically derived fluids. Results indicate that the damage zone of the Pliocene Boccheggiano fault represented the main channel for the flow of meteoric water, which was heated at depth, then mixed with high salinity fluids, and finally ascend to infiltrate along the older cataclastic levels. Our results, based on fluid inclusions, oxygen isotopic compositions and structural analyses indicate that a single fluid flow path run through the damage zone of the Boccheggiano fault and the older cataclasites, which were thus hydraulically connected.  相似文献   

On the effect of decreasing CO2 concentration in the atmosphere     

Isabella Bordi  Klaus Fraedrich  Alfonso Sutera  Xiuhua Zhu 《Climate Dynamics》2013,40(3-4):651-662

In the present paper the effect of an abrupt change of the atmospheric radiative forcing is investigated by means of a global climate model that includes a mixed layer ocean. In assessing if, under such a change, the model response has a bifurcation point, the steady solution is studied for a sudden decrease of CO₂ concentration from its actual value. It is found that there is a critical threshold for CO₂ content below which the model ends up to a snowball Earth. It occurs for a few percentage changes of CO₂ concentration around the threshold because the model strongly depends on the relationship among atmospheric temperature, water vapor content and the sudden ice-albedo feedback activation, even in the subtropical regions. Moreover, results suggest that the transition to ice-covered Earth is clearly favoured when Q-flux corrections (i.e. the parameterization of ocean heat transports) are removed.  相似文献   

Habitat characteristics,temporal variability,and macroinvertebrate communities associated with a mat-forming nuisance diatom (Didymosphenia geminata) in Catskill mountain streams,New York     

David C. Richardson  Isabella A. Oleksy  Timothy J. Hoellein  David B. Arscott  Catherine A. Gibson  Samantha M. Root 《Aquatic Sciences - Research Across Boundaries》2014,76(4):553-564

Didymosphenia geminata has recently and rapidly greatly expanded its range and abundance, sometimes as an exotic invasive and other times as a nuisance (‘native invader’) within its hypothesized native range, including the northeastern United States. D. geminata mats are visually conspicuous and can grow >10 cm thick. Mats first appeared in the eastern Catskill mountains (New York) in 2009. Our objectives were to (1) document D. geminata growth in three impounded or regulated rivers in the eastern Catskill mountains from 2010 to 2012 and (2) measure the effects of D. geminata mats on macroinvertebrates. The highest D. geminata cell densities were downstream of reservoir outflows in two of three streams. D. geminata mat development peaked in the summer each year, but maximum coverage and cell density was variable among years. D. geminata cover was negatively correlated with 10 days maximum antecedent shear stress, and the year with lowest mean D. geminata cover had multiple tropical storms and floods, suggesting that low variation in flow allows for D. geminata mat proliferation. Across sites, D. geminata density was negatively correlated with nitrate concentrations. D. geminata density was negatively related to macroinvertebrate richness suggesting that D. geminata mats may negatively affect aquatic food webs. D. geminata appears to be a nuisance species with similar habitat characteristics and growth where it is both a native invader and an invasive species.  相似文献