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991.
利用气象观测资料、NCEP/NCAR 1°×1°再分析资料以及GDAS资料,对2021年10月2-7日山西持续性强降水天气过程进行分析。结果表明:稳定的乌拉尔山低槽后部冷空气扩散,中纬度短波槽东移,与副热带高压外围西南暖湿气流持续交汇,同时高低空急流耦合形成强烈上升运动,低层切变线和地面辐合线稳定维持,及低层水汽不断输送并形成辐合,为持续性强降水的发生发展提供有利动力和水汽条件。此次强降水过程分为对流性降水和稳定性降水2个阶段,2阶段水汽输送通道的源地、路径、高度均有明显差异,但水汽输送贡献率均以对流层中低层山西南侧的水汽输送占主导地位。降水开始前,对流层中上层存在对称不稳定,大气可降水量明显跃增;对流性降水阶段,干空气不断入侵,对流不稳定快速建立与释放,对流层中低层水汽辐合区与强上升气流配合,导致山西出现强对流天气。地形的阻挡、抬升及地形收缩作用,对局地极端强降水具有增幅作用。 相似文献
992.
Konrad Miotliński 《Aquatic Geochemistry》2008,14(2):117-131
The reactive transport modeling of a complicated suite of reactions apparent in the aquifer during the application of N-containing
fertilizers is reported. The unconfined sandy aquifer can be subdivided into an oxic zone which contains groundwater with
oxygen and nitrate and an anoxic zone characterized by elevated iron and sulfate concentrations in groundwater. Oxygen and
nitrate are being reduced by pyrite and organic matter that commonly apparent in the aquifer. The oxidation of pyrite is modeled
using the local equilibrium approach, whereas decomposition of organic matter, with the adoption of kinetic approach. The
system is buffered by dissolution of aluminum and iron oxides. The modeling process is a two-step procedure. First, the processes
are modeled in the one-dimensional (1D) column using PHREEQC code. Subsequently, the calibrated and verified data were copied
and used in two-dimensional (2D) PHAST model. Prior to the performance of reactive transport modeling operations with PHAST,
a reliable flow model was executed. Finally, predictions are made for the distribution of water chemistry for the year 2008.
Model predicts that sulfate derived from the ongoing pyrite oxidation is reduced by the dissolved organic carbon at the higher
depth and forms pyrite by the reaction with iron. The results of this study highlight the importance of understanding the
interplay between the transport and chemical reactions that occur during the input of nitrate to the aquifer. Reactive transport
modeling incorporating the use of a newly developed code PHAST have proved to be a powerful tool for analyzing and quantifying
such interactions. 相似文献
993.
Influences of the unsaturated,saturated, and riparian zones on the transport of nitrate near the Merced River,California, USA 总被引:1,自引:0,他引:1
Joseph L. Domagalski Steven P. Phillips E. Randall Bayless Celia Zamora Carol Kendall Richard A. WildmanJr Janet G. Hering 《Hydrogeology Journal》2008,16(4):675-690
Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N2 in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area. 相似文献
994.
ANDREW J. WHEELER MAXIM KOZACHENKO DOUG G. MASSON VEERLE A. I. HUVENNE 《Sedimentology》2008,55(6):1875-1887
The Darwin Mounds are small (up to 70 m in diameter), discrete cold‐water coral banks found at c. 950 m water depth in the northern Rockall Trough, north‐east Atlantic. Formerly described in terms of their genesis, the Darwin Mounds are re‐evaluated here in terms of mound growth processes based on 100 and 410 kHz side‐scan sonar data. The side‐scan sonar coverage is divided into a series of acoustic facies representing increasing current speed and sediment transport/erosion from south to north: pockmark facies, ‘mounds within depressions’ facies, Darwin Mound facies, stippled seabed facies and sand wave facies. Mound morphometric changes are quantified and show a south‐to‐north divergence from an inherited morphology, reflecting the outline of coral‐colonized fluid escape structures, to developed, downstream elongated, elevated mound forms. It is postulated that increasing current speeds and bedload sand transport favour mound growth and development by a process of enhanced sand sedimentation within mounds due to current deceleration by frictional drag around coral colonies. Comparisons are made with similar growth processes attributed to comparably sized cold‐water coral mounds in the Porcupine Seabight, offshore Ireland. 相似文献
995.
贵州阿哈湖物质循环过程中的铁同位素地球化学及其指示意义 总被引:1,自引:0,他引:1
使用AGMP-1氯化物型阴离子交换树脂(100--200目)对夏季贵州阿哈湖流域水体悬浮颗粒物等样品进行了化学分离,并在多接收电感耦合等离子体质谱仪(MC-ICP-MS)上进行了铁同位素分析.分析结果表明,夏季阿哈湖湖水分层期间湖水悬浮颗粒物及各端员环境样品的铁同位素组成变化较大:湖水悬浮颗粒物的δ56Fe为负值,分布范围为-1.36‰~-0.10‰之间;各支流河水悬浮颗粒物的铁同位素组成在-0.88‰~-0.16‰之间;大气颗粒物的平均铁同位素组成为 0.06‰±0.02‰;而未经化学清洗的浮游藻类的铁同位素组成为 0.08‰.对比研究表明,湖水悬浮颗粒物的铁同位素组成不仅受各输入端员的影响,湖泊内部复杂的生物地球化学过程也对颗粒物的铁同位素组成产生了重要影响.陆源输入的颗粒有机结合态铁使得湖泊表层悬浮颗粒物的铁同位素组成偏低,而大气沉降颗粒物和湖泊表层的浮游藻类整体上对铁同位素组成的影响并不显著."ferrous wheel"铁循环对于氧化还原界面附近水层中铁同位素的重分配起到了主要的控制和影响作用.δ56Fe值与Fe/A1呈现良好的负相关关系,也显示出活性铁的循环迁移是造成氧化还原界面附近水层中悬浮颗粒物的铁同位素组成变化的重要原因,表明铁同位素与Fe/A1可能可以作为表征水体生物地球化学环境的良好指标. 相似文献
996.
The effects of air transportation on the movement of labor 总被引:1,自引:0,他引:1
The effects of the deregulation of airlines markets and the new technologies that have been introduced into air transportation
have been heavily studied. Much of this analysis has been on the impacts on the industry and the immediate welfare implications
for passengers and, to a lesser extent, cargo consignors. This study looks at the longer-term effects of the modern air transportation
system on labor markets and labor migration. The growth of the service sector, the emergence of more flexible manufacturing
techniques, the reduction in trade-barriers, and the creation of more sophisticated financial markets have led to greater
mobility in production and in capital movement. This has been explored to some extent. Labor is, however, also more mobile
- for example, since the admission of Poland to the European Union some 465,000 Polish workers have joined the UK labor market.
Air transportation facilitates easier migration, makes short-term, long-distance migration viable, and allows migrants to
maintain contact with their home country. Within larger countries, such as the US, there has also been a growth in long distance
“week-day” migration as spouses work in different parts of the country to be reunited at weekends. The study makes use of
aggregate data to look at trends in international labor movements particularly concerning the European situation, and, to
a lesser extent, at recent developments within the US. It is concerned both with what is going on in terms of the use being
made of air transportation by migrants and the light that this may shed on migration theory.
相似文献
Kenneth John ButtonEmail: |
997.
Stefan Gödeke Helmut Geistlinger Anko Fischer Hans-Hermann Richnow Mario Schirmer 《Environmental Geology》2008,55(6):1255-1261
Reactive tracer tests are performed to derive flow, transport and in situ biodegradation parameters. This paper describes
the 3D simulation of a reactive tracer test using the transition probability geostatistical approach. Fifty different equally
probable aquifer realizations were generated based on the geological information of 107 boreholes in an area of 62,500 m2. One realization was chosen for the reactive transport simulation based on the results of groundwater flow modeling and on
particle tracking calculations for the site. Field velocities at the site vary between 0.4 and 3 m/d. The transport of the
reactive tracers deuterium ring labeled toluene-d5 and fully deuterated toluene-d8 was simulated and first-order biodegradation rates of 0.017 d−1 for toluene-d5 and 0.012 d−1 for toluene-d8 were determined. 相似文献
998.
Estimates of regolith degradation in the McMurdo Dry Valleys of Antarctica are currently based on indirect evidence and ancient ashes at or near the soil surface that suggest excellent preservation of surfaces. On the other hand, the existing cosmogenic-nuclide surface exposure ages from many parts of the Dry Valleys are younger than the age of surface deposits inferred from stratigraphic relations. This suggests some combination of surface erosion or past ice cover, both of which would reduce the apparent exposure age. This paper quantifies the regolith degradation and/or past ice cover by measuring 10Be and 26Al from a landslide deposit that contains 11.3 Ma volcanic ash. The surface sample yields an apparent exposure age of only 0.4 Ma. However, measurements of the subsurface nuclide concentrations show that the deposit has not been shielded by ice, and that the age of the ash does not conflict with the apparent exposure age when slow degradation of the deposit (2 m Ma−1) is taken into account. Soil creep, which is a common degradational process in a wide variety of environments, is non-existent at this field site, which likely reflects the persistent lack of bio- and cryoturbation. 相似文献
999.
2017年春季,全国平均降水量139.1 mm,接近常年同期。从空间分布看,我国降水总体呈“西多东少”的分布型。全国平均气温11.1℃,较常年同期偏高0.7℃,全国大部地区气温接近常年同期或偏高。太平洋年代际涛动处在正位相,春季赤道中东太平洋海温正常略偏暖是造成中国春季气温偏暖的重要气候背景。同时,500 hPa高度和距平场上,亚洲北部(30°N以北)整体呈纬向型环流,东亚大槽位置偏东,全国大部主要受高度场正距平控制,从而有利于春季气温整体以偏暖为主。另外,1月赤道中东太平洋为弱的冷海温,其两侧的副热带地区和西太平洋均为暖水控制的异常分布,有利于出现春季华南和东北降水偏少,西南降水偏多的第二模态分布型。东北大部、华南和江南等地受北风距平控制,水汽以距平辐散为主,降水偏少;西南地区为来自孟加拉湾的暖湿气流与高原外围偏北气流交汇区,水汽异常辐合造成该地区降水偏多。 相似文献
1000.
K.-Y. Wang J. A. Pyle D. E. Shallcross S. M. Hall 《Journal of Atmospheric Chemistry》2001,40(2):123-170
In part 3 of this series of papers on a new 3-D global troposphericchemical transport model, using an Integrated Modelling System (IMS), anevaluation of the model performance in simulating global distributions andseasonal variations for volatile organic compounds (VOCs) in the atmosphere,is presented. Comparisons of model OH concentrations with previous modelstudies show consistent modelled OH levels from the subtropics tomidlatitudes, while more discrepancies occur over the tropical lowlatitudes, with IMS predicting the highest levels of OH. The close agreementbetween modelled OH concentrations over midlatitudes, where high surfaceNOxand VOC concentrations are also found, is indicative of the strongphotochemical coupling between NOx, VOCs and O3 overthese latitudes. IMSOH concentrations in the Northern Hemisphere (NH) midlatitudes during summerare generally lower than available measurements, implying that models ingeneral are underestimating OH levels at this location and time of year.Substantial differences between model OH concentrations over low latitudesclearly highlight areas of uncertainty between models. IMS OH concentrationsare the highest in general of the models compared, one possible reason isthat biogenic emissions of species such as isoprene and monoterpenes arehighest in IMS, leading to higher O3 levels and hence higher OH.Generally, the IMS VOC concentrations show a similar seasonality to themeasurements at most locations. In general though, IMS tends to underestimatethe NH wintertime VOC maximum and overestimate the NH summertime VOCminimum. Such an overestimate in summer could be due to IMSunderestimating OH levels, or an overestimation of VOC emissions or possiblya problem with model transport, all of these possibilities are explored.Except for n-pentane, the model underprediction of a VOC maximum during theNH winter month strongly suggests a missing emission mechanism in the modelor an underestimate of an existing one. It is very likely that there is alack of time varying emission sources in the model to account for theseasonal change in emission behaviour such as increasing energy usage (e.g.,electricity and gas), road transportation, engine performance, and otheranthropogenic factors which show strong seasonal characteristics. Theanomalous overprediction of wintertime n-pentane compared with its closesummertime prediction with the measurements suggest that emissions in thiscase may be too high. 相似文献