Idealized Large-Eddy Simulations of Sea and Lake Breezes: Sensitivity to Lake Diameter, Heat Flux and Stability     

Erik T. Crosman  John D. Horel 《Boundary-Layer Meteorology》2012,144(3):309-328

Idealized large-eddy simulations of lake and sea breezes are conducted to determine the sensitivity of these thermally-driven circulations to variations in the land-surface sensible heat flux and initial atmospheric stability. The lake-breeze and sea-breeze metrics of horizontal wind speed, horizontal extent, and depth are assessed. Modelled asymmetries about the coastline in the horizontal extent of the low-level onshore flow are found to vary as a function of the heat flux and stability. Small lake breezes develop similarly to sea breezes in the morning, but have a significantly weaker horizontal wind-speed component and a smaller horizontal extent than sea breezes in the afternoon.  相似文献   

Quality of geological CO2 storage to avoid jeopardizing climate targets     

Asbj?rn Torvanger  Alv-Arne Grimstad  Erik Lindeberg  Nathan Rive  Kristin Rypdal  Ragnhild Bieltvedt Skeie  Jan Fuglestvedt  Petter Tollefsen 《Climatic change》2012,114(2):245-260

We explore allowable leakage for carbon capture and geological storage to be consistent with maximum global warming targets of 2.5 and 3 °C by 2100. Given plausible fossil fuel use and carbon capture and storage scenarios, and based on modeling of time-dependent leakage of CO₂, we employ a climate model to calculate the long-term temperature response of CO₂ emissions. We assume that half of the stored CO₂ is permanently trapped by fast mechanisms. If 40?% of global CO₂ emissions are stored in the second half of this century, the temperature effect of escaped CO₂ is too small to compromise a 2.5 °C target. If 80?% of CO₂ is captured, escaped CO₂ must peak 300?years or later for consistency with this climate target. Due to much more CO₂ stored for the 3 than the 2.5 °C target, quality of storage becomes more important. Thus for the 3 °C target escaped CO₂ must peak 400?years or later in the 40?% scenario, and 3000?years or later in the 80?% scenario. Consequently CO₂ escaped from geological storage can compromise the less stringent 3 °C target in the long-run if most of global CO₂ emissions have been stored. If less CO₂ is stored only a very high escape scenario can compromise the more stringent 2.5 °C target. For the two remaining combinations of storage scenarios and climate targets, leakage must be high to compromise these climate targets.  相似文献   

Replacement of magnetite by pyrite under hydrothermal conditions     

Gujie Qian  Allan Pring  Joël Brugger  William M. Skinner  Guorong Chen 《Journal of Geochemical Exploration》2009

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Geochemical distribution of arsenic,cadmium, lead and zinc in river sediments affected by tailings in Zimapán,a historical polymetalic mining zone of México     

Erik Espinosa  María Aurora Armienta  Olivia Cruz  Alejandra Aguayo  Nora Ceniceros 《Environmental Geology》2009,58(7):1467-1477

High arsenic (As) groundwater is widely distributed in northwestern Hetao Plain, an arid region with sluggish groundwater flow. Observed As concentration in groundwater from wells ranges from 76 to 1,093 μg/l. Most water samples have high total dissolved solids, with Cl and HCO₃ as the dominant anions and Na as the dominant cation. The major hydrochemical types of most saline groundwaters are Na–Mg–Cl–HCO₃ and Na–Mg–Cl. By contrast, fresh groundwaters generally belong to the Na–Mg–HCO₃ type. High concentrations of arsenic in shallow aquifers are associated with strongly reducing conditions, as evidenced by high concentrations of dissolved organic carbon, ammonium, as well as dissolved sulfide and Fe, dominance of arsenite, relatively low concentrations of nitrate and sulfate, and occasionally high content of dissolved methane (CH₄). High As groundwaters from different places at Hetao Plain experienced different redox processes. Fluoride is also present in high As groundwater, ranging between 0.40 and 3.36 mg/l. Although fluorosis poses an additional health problem in the region, it does not correlate well with As in spatial distribution. Geochemical analysis indicates that evapotranspiration is an important process controlling the enrichment of Na and Cl, as well as trace elements such as As, B, and Br in groundwater. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Groundwater exploration and evaluation by using geophysical interpretation (case study: Al Qantara East, North Western Sinai, Egypt)     

Sultan Awad Sultan  Hatem M. Mekhemer  Fernando M. Santos 《Arabian Journal of Geosciences》2009,2(3):199-211

Different geophysical tools such as geoelectric, gravity, and magnetic have been applied to detect groundwater potentiality and structural elements, which controlled a geometry of the groundwater aquifers in the study area. Nineteen vertical electrical soundings measured using ABEM SAS 4000 equipment through Schlumberger configuration of AB/2 ranged from 1.5 to 1,000 m; the quantitative interpretation was carried out using manual and analytical techniques. The results of quantitative interpretation used to construct six geoelectrical cross-sections indicate that the subsurface sequence of the study area consists of seven geoelectrical units. These units are Quaternary sand sheet and sand dunes, Quaternary aquifer, marly limestone, clay, sandy clay, clay with sandstone intercalation, and deep Nubian sandstone aquifer. The isopach map of the Quaternary aquifer exhibits thickness of the Quaternary aquifer that increased at the northern and southern part (50 m) and decreased at the eastern and western part (5 m), and the depth of the aquifer increased at the northern part (40 m) and decreased at the central part to 6 m. The isoresistivity map of the aquifer shows a high resistivity at the northern part but the southern part reveals low resistivity according to the lithology. The water salinity increases in the direction of groundwater flow from 500 to 10,500 mg/l. The low water salinity is due to direct recharge from El-Sheikh Zayed Canal, which supplied fresh water to this area. Sixty-five gravity stations were measured using Auto-Grav gravity meter; different gravity corrections were applied on raw data. The corrected gravity values were plotted to represent a Bouguer anomaly map; the residual gravity anomaly map was used for delineation of the fault elements. The area was dissected by different fault elements of trends NW–SE, NE–SW, and E–W. In addition, 65 ground magnetic stations were measured at the same sites of gravity stations. The results of magnetic interpretation indicate that the depth of the basement is shallow at the western and southern parts of the area (4,500 m), but the central part exhibits greater depth of 7,900 m.

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الملخص العربي   طرق جيوفيزيقية مختلفة مثل الكهربية الأرضية, التناقلية الأرضية والمغناطيسية الأرضية تم تطبيقها لتحديد إمكانية تواجد المياه الجوفية والتراكيب الجيولوجية التي تتحكم في إبعاد وهندسة الخزان الجوفي في منطقة الدراسة. تسعة عشر جسة كهربية عمودية تم قياسها باستخدام جهاز من شركة (ِ ABEM) ساس 4000 من خلال تشكيل شلمبرجير بمسافة بين القطبين أب /2 تبدأ من 1.5 متر حتى 1000 متر, التفسير الكمي تم علي البيانات باستخدام التفسير اليدوي والتحليلي. نتائج التفسير الكمي تم استخدامها لتشييد ست قطاعات جيوكهربية والتي أوضحت أن التتابع التحت سطحي لمنطقة الدراسة يتكون من سبعة وحدات جيوكهربية. هذه الوحدات هي صفائح من الرمال والكثبان الرملية للعصر الرباعي, الخزان الجوفي الرباعي, حجر جيري مارلي, طفلة, طفله رمليه, طفله متداخلة مع الرمل والخزان الجوفي النوبي. خريطة السمك للخزان الجوفي الرباعي تظهر أن سمك الخزان الجوفي الرباعي يزيد عند شمال وجنوب منطقة الدراسة (50 متر) ويقل عند الجزء الشرقي والغربي (5 متر). وعمق هذا الخزان الجوفي الرباعي يزيد عند الجزء الشمالي (40 متر) وينقص عمق الخزان الرباعي عمد وسط المنطقة (6 متر). خريطة المقاومة الحقيقية للخزان الجوفي الرباعي تبين أن المقاومة تزيد عند الجزء الشمالي وتقل المقاومة عند الجزء الجنوبي من منطقة الدراسة بناءا علي التكوين الصخري للطبقات. ملوحة المياه الجوفية تزيد في اتجاه سريان المياه من 500 مليجرام/لتر إلي 10500 مليجرام/لتر. نقص الملوحة المياه ناتج عن التسرب المباشر من قناة الشيخ زايد والتي تعتبر مصدر المياه العزبة في منطقة الدراسة. خمس وستون محطة تثاقيلية أرضية تم قياسها باستخدام اوتو-جرافميتر, العديد من تصحيحات الجاذبية الأرضية نم تطبيقها علي البيانات الأصلية. قراءات الجاذبية الأرضية المصححة تم رسمها علي خريطة لتمثل شاذات البوجير وتم استخدام خريطة الشاذات المحلية لتجديد التراكيب الجيولوجية (الفوالق). حيت أوضحت الدراسة أن المنطقة تأثرت بعده فوالق باتجاهات مختلفة مثل شمال غرب- جنوب شرق, شمال شرق-جنوب غرب وشرق-غرب. نتيجة تفسير بيانات المغناطيسية الأرضية أظهرت أن عمق ضجور القاعدة تكون ضحلة عند الجزء الغربي والجنوبي (4500 متر) وتكون ضجور القاعدة عميقة (7900 متر) عند الجزء الأوسط من منطقة الدراسة.

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Using Föhn conditions to characterize urban and regional sources of particles     

D. Mira-Salama  R. Van Dingenen  C. Gruening  J.-P. Putaud  F. Cavalli  P. Cavalli  N. Erdmann  A. Dell'Acqua  S. Dos Santos  J. Hjorth  F. Raes  N.R. Jensen   《Atmospheric Research》2008,90(2-4):159-ICNAA07

Characterizations of urban and regional sources of particulate matter (PM) were performed in the Milan area (North of Italy) during Föhn and stagnant (non-Föhn) conditions. The measurements were performed at two different places: in an urban area North of Milan (Bresso) and in a regional area at the EMEP-GAW station in Ispra (about 65 km NW from Milan) during the winter periods of the years 2002–2007. Particle size distributions and chemical bulk analysis of aerosols are combined with single particle mass spectrometry to obtain information about the chemical content of the particles and their mixing state. Föhn conditions are characterized by extremely clean background air from which background aerosol is scavenged, and consequently local sources (here defined as sources between the sampling sites and the mountain range top about 100–150 km away depending on the wind direction) determine the aerosol properties.It was observed that during Föhn events the accumulation mode in the size range 50 nm < d < 300 nm practically disappears and that the size fraction below 50 nm dominates the total number distribution. The significant change in the number size distribution and the large decrease in PM10 mass during Föhn events are accompanied by a significant change in the chemical composition of the particles. Results from bulk chemical analysis showed high amounts of carbonaceous compounds and very low concentrations of ammonium nitrate (as indicator for secondary chemistry) during Föhn episodes, in contrast to stagnant conditions, when secondary components are dominating the aerosol composition. Single particle measurements confirm the high contribution of carbonaceous compounds in locally emitted particles.It was concluded that particles that originated in the urban area come mainly from combustion processes, especially direct traffic emissions, domestic heating and industrial activities, whereas the regionally emitted particles are different with much less traffic contribution.We estimate that under prevailing (non-Föhn) winter conditions, about 50–65% of the aerosol mass load in the city of Milan are caused by local emissions, and about 35–50% come from regional background. This finding suggests that in order to improve air quality in a big city like Milan, it is important to combine local traffic restriction interventions with other long-term regional scale air-quality-measures.  相似文献   

Similar-sized collisions and the diversity of planets     

Erik Asphaug 《Chemie der Erde / Geochemistry》2010,70(3):199-219

It is assumed in models of terrestrial planet formation that colliding bodies simply merge. From this the dynamical and chemical properties (and habitability) of finished planets have been computed, and our own and other planetary systems compared to the results of these calculations. But efficient mergers may be exceptions to the rule, for the similar-sized collisions (SSCs) that dominate terrestrial planet formation, simply because moderately off-axis SSCs are grazing; their centers of mass overshoot. In a “hit and run” collision the smaller body narrowly avoids accretion and is profoundly deformed and altered by gravitational and mechanical torques, shears, tides, and impact shocks. Consequences to the larger body are minor in inverse proportion to its relative mass. Over the possible impact angles, hit-and-run is the most common outcome for impact velocities v_imp between $～1.2$ and 2.7 times the mutual escape velocity v_esc between similar-sized planets. Slower collisions are usually accretionary, and faster SSCs are erosive or disruptive, and thus the prevalence of hit-and-run is sensitive to the velocity regime during epochs of accretion. Consequences of hit-and-run are diverse. If barely grazing, the target strips much of the exterior from the impactor—any atmosphere and ocean, much of the crust—and unloads its deep interior from hydrostatic pressure for about an hour. If closer to head-on $(～30\text{–}45°)$ a hit-and-run can cause the impactor core to plow through the target mantle, graze the target core, and emerge as a chain of diverse new planetoids on escaping trajectories. A hypothesis is developed for the diversity of next-largest bodies (NLBs) in an accreting planetary system—the bodies from which asteroids and meteorites derive. Because nearly all the NLBs eventually get accreted by the largest (Venus and Earth in our terrestrial system) or by the Sun, or otherwise lost, those we see today have survived the attrition of merger, evolving with each close call towards denser and volatile-poor bulk composition. This hypothesis would explain the observed density diversity of differentiated asteroids, and of dwarf planets beyond Neptune, in terms of episodic global-scale losses of rock or ice mantles, respectively. In an event similar to the Moon-forming giant impact, Mercury might have lost its original crust and upper mantle when it emerged from a modest velocity hit and run collision with a larger embryo or planet. In systems with super-Earths, profound diversity and diminished habitability is predicted among the unaccreted Earth-mass planets, as many of these will have be stripped of their atmospheres, oceans and crusts.  相似文献   

Subducted seamounts in an eclogite-facies ophiolite sequence: the Andean Raspas Complex, SW Ecuador   总被引：1，自引：0，他引：1  

Timm John  Erik E. Scherer  Volker Schenk  Petra Herms  Ralf Halama  Dieter Garbe-Schönberg 《Contributions to Mineralogy and Petrology》2010,159(2):265-284

The metamorphic Raspas Complex of southwest Ecuador consists of high-pressure mafic, ultramafic, and sedimentary rocks. The Lu–Hf ages of a blueschist, a metapelite, and an eclogite overlap at around 130 Ma and date high-pressure garnet growth. Peak metamorphic conditions in the eclogites reached 1.8 GPa at 600°C, corresponding to a maximum burial depth of ~60 km. The geochemical signatures of the eclogites suggest that their protoliths were typical mid-ocean ridge basalts (MORB), whereas the blueschists exhibit seamount-like characteristics, and the eclogite-facies peridotites seem to represent depleted, MORB-source mantle. That these rocks were subjected to similar peak PT conditions contemporaneously suggests that they were subducted together as an essentially complete section within the slab. We suggest that this section became dismembered from the slab during burial at great depth—perhaps as a consequence of scraping off the seamounts. The spatially close association of MORB-type eclogite, seamount-type blueschist, serpentinized peridotite, and metasediments points to an exhumed high-pressure ophiolite sequence.  相似文献   

Timing of eclogite facies metamorphism in the southernmost Scandinavian Caledonides by Lu–Hf and Sm–Nd geochronology     

Matthijs A. Smit  Erik E. Scherer  Michael Bröcker  Herman L. M. van Roermund 《Contributions to Mineralogy and Petrology》2010,159(4):521-539

The Scandinavian Caledonides contain several non-cogenetic eclogite-bearing terranes that were metamorphosed before the main orogenic stage in Scandian time (430–395 Ma). Although petrological and geochronological data from these terranes have provided essential information on the geodynamic history of the Caledonian orogenic cycle, the general picture is still patchy. To refine existing geodynamic models, we have dated the eclogite occurrence in the Jæren nappe, SW Norway, by Lu–Hf and Sm–Nd geochronology. Five out of the six studied samples provide a weighted mean Lu–Hf age of 469.9 ± 1.2 Ma (±2σ). One sample provided a significantly younger age of 457.9 ± 2.4 Ma. Garnet from the younger sample grew exclusively at eclogite facies conditions. In contrast, garnet from the other samples comprises prograde cores and peak metamorphic rims. Age estimates that take Lu-contributions of each zone into account provide an age of 471.0 ± 0.9 Ma for the cores and suggest a ca. 455 Ma age for the rims, which is identical to the bulk-garnet age of the younger sample. The same pattern is indicated by Sm–Nd ages, although these are relatively imprecise and reflect isotopic disturbance during thermal overprinting upon exhumation. The data define a new high-pressure age population for the Scandinavian Caledonides, which allows more detailed insight into the subduction history that affected the Baltoscandian margin before Scandian continental collision. Furthermore, this study highlights the potential complexities involved in garnet geochronology and shows the strength of Lu–Hf dating for unraveling the geochronological record of HP rocks.  相似文献   

Sulfur isotope fractionation during the May 2003 eruption of Anatahan volcano, Mariana Islands: Implications for sulfur sources and plume processes     

J. Maarten de Moor  Tobias P. Fischer  Erik H. Hauri  Viorel Atudorei 《Geochimica et cosmochimica acta》2010,74(18):5382-5397

Sulfur isotope compositions of pumice and adsorbed volatiles on ash from the first historical eruption of Anatahan volcano (Mariana arc) are presented in order to constrain the sources of sulfur erupted during the period 10-21 May, 2003. The isotopic composition of S extracted from erupted pumice has a narrow range, from δ³⁴S_V-CDT +2.6‰ to +3.2‰, while the composition of sulfur adsorbed onto ash has a larger range (+2.8‰ to +5.3‰). Fractionation modeling for closed and open system scenarios suggests that degassing of SO₂ raised the δ³⁴S_V-CDT value of S dissolved in the melt from an initial composition of between +1.6‰ and +2.6‰ for closed-system degassing, or between −0.5‰ and +1.5‰ for open-system degassing, however closed-system degassing is the preferred model. The calculated values for the initial composition of the magma represent a MORB-like (δ³⁴S_V-CDT ∼ 0‰) mantle source with limited contamination by subducted seawater sulfate (δ³⁴S_V-CDT +21‰). Modeling also suggests that the δ³⁴S_V-CDT value of SO₂ gas in closed-system equilibrium with the degassed magma was between +0.9‰ and +2.5‰. The δ³⁴S_V-CDT value of sulfate adsorbed onto ash in the eruption plume (+2.8‰ to +5.1‰) is consistent with sulfate formation by oxidation of magmatic SO₂ in the eruption column. The sulfur isotope composition of sulfate adsorbed to ash changes from lower δ³⁴S values for ash erupted early in the eruption to higher δ³⁴S values for ash erupted later in the eruption. We interpret the temporal/stratigraphic change in sulfate isotopic composition to primarily reflect a change in the isotopic composition of magmatic SO₂ released from the progressively degassing magma and is attributed to the expulsion of an accumulated gas phase at the beginning of the eruption. More efficient oxidation of magmatic SO₂ gas to sulfate in the early water-rich eruption plume probably contributed to the change in S isotope compositions observed in the ash leachates.  相似文献