Energetics of Indian winter monsoon

The Indian subcontinent is characterized by complex topography and heterogeneous land use-land cover. The Himalayas and the Tibetan Plateau are spread across the northern part of the continent. Due to its highly variable topography, understanding of the prevailing synoptic weather systems is complex over the region. The present study analyzes the energetics of Indian winter monsoon (IWM) over the Indian subcontinent using outputs of mesoscale model (MM5) forced with National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), US, initial and boundary conditions. MM5 modeling framework, designed to simulate or predict mesoscale atmospheric circulations, is having a limited-area, non-hydrostatic and terrain following 12 sigma levels. The IWM energetics is studied using MM5 model outputs. Prior to this model’s validity and deviation from the corresponding observations (NCEP/NCAR) is assessed. The model’s overestimation/underestimation of wind, temperature and specific humidity at upper troposphere proves that the model has difficulty in picking up corresponding fields at all the model grid points because of terrain complexity over the Himalayas and Tibetan Plateau. Hence, the model fields deviate from the corresponding observations. However, model results match well with the winter global energy budget calculated using reanalysis dataset by Peixoto and Oort (1992). It suggests MM5 model’s fitness in simulating large scale synoptic weather systems. And, thus the model outputs are used for calculation of energetics associated with IWM. It is observed that beyond \(15^{{\circ }}\hbox {N}\) lower as well as upper level convergence of diabatic heating, which represents continental cooling and sinking of heat from atmosphere to land mass (i.e., surface is cooler than surrounding atmosphere) dominates. The diabatic heating divergence (cooling of continents) is found over ocean/sea and whole of the China region, Tibetan and central Himalayas (because of excess condensation than evaporation). The adiabatic generation of kinetic energy depends on the cross isobaric flow (north to south in winter, i.e., the present study shows strong circulation during IWM). It is found that wind divergence of model concludes lower level convergence over study region (i.e., strong winter circulation in the model fields).     

三维稀疏反演多次波预测及曲波域匹配相减技术

传统的自由表面多次波压制(SRME)方法研究是基于二维假设的,这种算法对多次波贡献考虑过于局限,难以应对复杂地质构造的情况。3DSRME算法过于笨拙,对数据要求过于苛刻,很难有效推广和应用。三维稀疏反演多次波预测方法利用柯西概率密度函数,将垂直测线方向上稀疏的多次波能量贡献道集转换到模型空间,有效重构同相轴能量顶点——菲涅尔带,从而有效拾取多次波能量,准确预测多次波。采用曲波域匹配相减技术对多次波进行去除,相较于传统的最小平方匹配相减方法,Curvelet域具有多方向、多尺度的特性,能够更有效地压制多次波。建立三维倾斜层状速度模型,对模拟三维地震数据进行试算,并与常规2D SRME的处理结果进行对比,验证了本文所述方法的有效性。     

新江湾城开发区表层土壤中有机氯农药和多氯联苯的分布特征

利用电子捕获检测器气相色谱法(GC-ECD)测定新江湾城表层土壤中有机氯农药(OCPs)和多氯联苯(PCBs),六六六类(HCHs)和滴滴涕类(DDTs)化合物均被检出,HCHs含量为0.81~2.84 ng/g,平均1.90 ng/g;DDTs含量为9.37~130.8 ng/g,平均43.9 ng/g。HCHs都未超过国家土壤环境质量标准的一级水平,但是有两个站点的DDTs超过国家土壤环境质量标准的一级水平。7种多氯联苯(7PCBs)含量为1.83~8.46 ng/g,平均3.99 ng/g,以四氯代PCB 52和六氯代PCB 138残留最高。PCBs污染主要集中在火力发电厂处,并向周边蔓延,反映了PCBs污染的来源与电力设备有关,其污染来源很有可能来自历史上变压器油泄漏物的残留及来自工业区的新的PCBs输入。     

Continuously unique anisotropic critical state hyperplasticity

This paper presents the theoretical development and methodological motivation of a single surface anisotropic hyperplasticity model. The model extends the isotropic family of models developed by Coombs and Crouch by: (i) introducing anisotropic shearing into the yield surface, (ii) relating two of the material constants to a single physical quantity and (iii) using a more physically realistic pressure sensitive elastic free energy function. This model overcomes the difficulty of determining the constants of the isotropic two‐parameter surface by analytically relating them to a single experimentally measurable physical quantity, namely the normalised hydrostatic position of the Critical State. This provides a model with a Critical State surface that is constant throughout the loading process, invariant of the level of anisotropy inherent in the yield envelope. The model is compared with experimental data from triaxial tests on Lower Cromer Till, contrasted against the SANIclay model and the recent model of Yang et al. (2015) as well as being compared with rarely considered experimental data from hollow cylinder tests on London Clay. Copyright © 2016 John Wiley & Sons, Ltd.     

A new versatile constitutive law for modelling the monotonic response of soft rocks and structured fine-grained soils

This paper deals with a new critical state–based constitutive model for soft rocks and fine-grained soils. The model, formulated in the single-surface plasticity framework, is characterised by the following main features: (i) a generalised three-invariant yield surface capable of reproducing a wide set of well-known criteria, (ii) the dependency of the elastic stiffness on the current stress state by means of a hyperelastic formulation, (iii) the ability of simulating the plastic strain–driven structure degradation processes by a set of appropriate isotropic hardening laws, and (iv) a nonassociate flow rule in the meridian plane. The adopted formulation is hierarchical, such that the various features of the model can be activated or excluded depending on the specific kind of geomaterial to be modelled and on the quality and quantity of the related available experimental results. The constitutive model was implemented in a commercial finite element code by means of an explicit modified Euler scheme with automatic substepping and error control. The procedure does not require any form of stress correction to prevent drift from the yield surface. The performance of the model is first analysed by means of a wide set of parametric analyses, in order to highlight the main features and to evaluate the sensitivity of the formulation with reference to the input parameters. The model is then adopted to simulate the experimental response observed on three different geomaterials, ranging from soft clays to soft rocks.     

An investigation of upper mantle heterogeneity beneath the Archaean and Proterozoic crust of western Canada from Lithoprobe controlled-source seismic experiments

Observations of upper mantle reflectivity at numerous locations around the world have been linked to the presence of a heterogeneous distribution of rock types within a broad layer of the upper mantle. This phenomenon is observed in wide-angle reflection data from Lithoprobe's Alberta Basement Transect [the SAREX and Deep Probe experiments of 1995] and Trans-Hudson Orogen Transect [the THoRE experiment of 1993]. SAREX and Deep Probe image the Archaean lithosphere of the Hearne and Wyoming Provinces, whereas THoRE images the Archaean and Proterozoic lithosphere of the Trans-Hudson Orogen and neighbouring areas.Finite-difference synthetic seismograms are used to constrain the position and physical properties of the reflective layer. SAREX/Deep Probe modelling uses a 2-D visco-elastic finite-difference routine; THoRE modelling uses a pseudospectral algorithm. In both cases, the upper mantle is parameterized in terms of two media. One medium is the background matrix; the other is statistically distributed within the first as a series of elliptical bodies. Such a scheme is suitable for modelling: (1) variations in lithology (e.g., a peridotite matrix with eclogite lenses) or (2) variations in rheology (e.g., lenses of increased strain within a less strained background).The synthetic seismograms show that the properties of heterogeneities in the upper mantle do not change significantly between the two Lithoprobe transects. Beneath the Trans-Hudson Orogen in Saskatchewan, the layer is best modelled to lie at depths between 80 and 150 km. Based on observations from perpendicular profiles, anisotropy of the heterogeneities is inferred. Beneath the Precambrian domains of Alberta, 400 km to the west, upper mantle heterogeneities are modelled to occur between depths of 90 and 140 km. In both cases the heterogeneous bodies within the model have cross-sectional lengths of tens of kilometers, vertical thicknesses less than 1 km, and velocity contrasts from the background of − 0.3 to − 0.4 km/s. Based on consistency with complementary data and other results, the heterogeneous layer is inferred to be part of the continental lithosphere and may have formed through lateral flow or deformation within the upper mantle.     

One-dimensional thermal modelling of Acadian metamorphism in southern Vermont, USA

One‐dimensional thermal (1DT) modelling of an Acadian (Devonian) tectonothermal regime in southern Vermont, USA, used measured metamorphic pressures and temperatures and estimated metamorphic cooling ages based on published thermobarometric and geochronological studies to constrain thermal and tectonic input parameters. The area modelled lies within the Vermont Sequence of the Acadian orogen and includes: (i) a western domain containing garnet‐grade pre‐Silurian metasedimentary and metavolcanic rocks from the eastern flank of an Acadian composite dome structure (Rayponda–Sadawga Dome); and (ii) an eastern domain containing similar, but staurolite‐ or kyanite‐grade, rocks from the western flank of a second dome structure (Athens Dome), approximately 10 km farther east. Using reasonable input parameters based on regional geological, petrological and geochronological constraints, the thermal modelling produced plausible P–T paths, and temperature–time (T –t) and pressure–time (P–t) curves. Information extracted from P–T –t modelling includes values of maximum temperature and pressure on the P–T paths, pressure at maximum temperature, predicted Ar closure ages for hornblende, muscovite and K‐feldspar, and integrated exhumation and cooling rates for segments of the cooling history. The results from thermal modelling are consistent with independently obtained pressure, temperature and Ar cooling age data on regional metamorphism in southern Vermont. Modelling results provide some important bounding limits on the physical conditions during regional metamorphism, and indicate that the pressure contemporaneous with the attainment of peak temperature was probably as much as 2.5 kbar lower than the actual maximum pressure experienced by rocks along various particle paths. In addition, differences in peak metamorphic grade (garnet‐grade versus staurolite‐grade or kyanite‐grade) and peak temperature for rocks initially loaded to similar crustal depths, differences in calculated exhumation rates, and differences in ⁴⁰Ar/³⁹Ar closure ages are likely to have been consequences of variations in the duration of isobaric heating (or ‘crustal residence periods’) and tectonic unroofing rates. Modelling results are consistent with a regional structural model that suggests west to east younging of specific Acadian deformational events, and therefore diachroneity of attainment of peak metamorphic conditions and subsequent ⁴⁰Ar/³⁹Ar closure during cooling. Modelling is consistent with the proposition that regional variations in timing and peak conditions of metamorphism are the result of the variable depths to which rocks were loaded by an eastward‐thickening thrust‐nappe pile rooted to the east (New Hampshire Sequence), as well as by diachronous structural processes within the lower plate rocks of the Vermont Sequence.     

耕作措施对陕西耕作土壤碳储量的影响模拟*

鉴于农业生态系统土壤有机碳(SOC)平衡对中国农业可持续发展的重要性,文章以陕西农业生态系统为对象,整合农业生物地球化学模型(DNDC)与陕西农业地理信息系统数据库,利用陕西地区气象和作物资料,对陕西省2000年作物生长发育和土壤碳循环进行了模型模拟,实例探讨了耕作管理对土壤碳储量的影响,并由此评价生物地球化学模型在气候变化、土壤性质及农业耕作管理措施对土壤碳含量影响方面的预测能力。敏感性分析表明土壤性状,尤其是初始有机碳含量是影响模型区域尺度模拟的最主要敏感因素。区域模拟使用灵敏系数分析法,分别采用敏感因子的最大、最小值驱动模型在每一模拟单元内的运算,以产生一个土壤有机碳变化的范围值,土壤有机碳变化的真实值应以较大机率包含在这一范围内。分析模拟结果可以得出3点结论: 1)2000年陕西耕作土壤总有机碳储量约为103TgC,是一个大气CO₂源,向大气释放碳0.5TgC; 2)提高作物秸秆还田率是提高陕西农田碳库储量的有效可行措施,将作物秸秆还田率从当前的15 ％ 提高到50 ％ 或90 ％ 会使陕西农田土壤从大气CO₂源转变为汇,每年分别增加土壤有机碳库储量0.7TgC或2.1TgC; 3)施用有机农肥(500kg/hm²)也会增加土壤碳输入,从而提高土壤碳储量,使陕西农田系统转变为较弱的碳(C)源,每年可多固定0.2TgC。     

南海南部深水多次波模拟分析与压制处理

南海南部陆缘构造复杂多变,海底崎岖不平,造成该区多道地震资料多次波十分发育且混杂复杂绕射波。为了识别深层有效反射信息、压制多次波,首先通过正演模拟分析深水条件下多次波的传播规律和特征,然后对复杂理论Pluto模型进行详细处理并试验了几种典型多次波压制方法,寻找到一套有效的多次波压制处理思路:通过表面相关多次波衰减(SRME)法降低多次波能量级别,运用τ-p域预测反褶积压制周期规律的近中道多次波,再在此基础上灵活运用高分辨率抛物线Radon变换对共反射点道集(CRP)进行中远道多次波压制。理论模型和礼乐盆地海区的实际资料处理结果表明,该方法能够较大程度上压制深水资料多次波并增强对深部有效信息的识别。     

Hydrodynamic modelling of some metamorphic processes

The P–T paths for metamorphic complexes from the Precambrian shields and fold belts of different ages may result from advection, i.e. one-cycle convective processes in the lithosphere. This conclusion has been exemplified by the metamorphic evolution of several well-known complexes, for which an advective model can be successfully applied. Numerical simulations of the above processes in terms of Newtonian rheology by using a two-dimensional finite element program have been conducted.
Two representative models for intracontinental gravitational ordering initiated presumably by mantle activity are considered: (i) a thermally activated multi-layered rhythmic sequence and (ii) huge rising diapiars causing circulation, in which crustal lithologies underwent high- P metamorphism (above 10–15 kbar) and subsequent ascent toward the Earth's surface.     

Stochastic continuum modeling of flow and transport in a crystalline rock mass: Fanay-Augères,France, revisited

A stochastic discrete-fracture model was used by Cacas et al.^a,b to interpret flow measurements and transport experiments in a fractured crystalline rock mass at Fanay-Augères. They considered continuum models to be incapable of properly interpreting small-scale measurements or tracer tests in fractured systems, which, in their view, require three-dimensional modeling of numerous discrete channels; in their opinion, continuum modeling applies only to average flow on a relatively large scale. Cacas et al. considered their discrete fracture model to have been validated by its demonstrated ability to reproduce selected experimental results. In this paper, flow and transport at Fanay-Augères are modeled by viewing the fractured rock as a stochastic continuum in a manner originally proposed by Neuman^c,d. The stochastic continuum approach obviates the need for detailed information about fracture geometry or assumptions about how individual fractures control flow and transport. All it requires is the delineation of a few dominant features, which can be embedded into the stochastic continuum model as heterogeneous porous slabs. Though a fault zone has been identified at the Fanay-Augères experimental site, it has been modeled neither by Cacas et al. nor in this paper. In fact, in this paper, a larger selection of experimental results than those considered by Cacas et al. are reproduced merely by modeling the rock as a statistically homogeneous continuum in two dimensions. These results demonstrate that a continuum approach may be well suited for the analysis of flow and transport in fractured rock. This does not constitute a validation of the continuum approach, just as the results of Cacas et al. fall short of validating the discrete fracture approach. Instead, the two sets of results illustrate jointly the well-established principle that an open system, especially one as complex as fractured hydrogeologic environments tend to be, cannot be described uniquely on the basis of sparse data and need not be described in great detail to capture its salient behavior by a model.^a Cacas MC, Ledoux E, de Marsily G, Barbreau A, Calmels P, Gaillard B, Margritta R (1990a) Modelling fracture flow with a stochastic discrete fracture network: calibration and validation. 1. The flow model. Water Resour Res 26(3):479–489^b Cacas MC, Ledoux E, de Marsily G, Barbreau A, Calmels P, Gaillard B, Margritta R (1990b) Modelling fracture flow with a stochastic discrete fracture network: calibration and validation. 2. The transport model. Water Resour Res 26(3):491–500^c Neuman SP (1987) Stochastic continuum representation of fractured rock permeability as an alternative to the REV and fracture network concepts, in Rock Mechanics. In: Farmer IW, Daemen JJK, Desai CS, Glass CE, Neuman SP (eds) Proceedings of the 28th U.S. Symposium, Tucson, Arizona. Balkema, Rotterdam, pp 533–561^d Neuman SP (1988) A proposed conceptual framework and methodology for investigating flow and transport in Swedish crystalline rocks. SKB Swedish Nuclear Fuel and Waste Management Co., Stockholm, September, Arbetsrapport 88–37, 39 pp     

The practice of Integrated Water Resources Management in South Africa: challenges of women in water user associations

South Africa’s National Water Act and National Water Resource Strategy set out an ambitious societal vision with a strong focus on the redistribution of water resources towards the marginalised and on empowering historically disadvantaged communities including women. This vision is reflected in the framework for Integrated Water Resources Management (IWRM) that acknowledges women as pivotal in water management practices. Based on this premise, this paper examines the challenges women face in performing their roles in IWRM in rural South Africa. It draws on a study of a water user association that operates in the Limpopo Province of South Africa. The design of the study was qualitative in nature with a semi-structured interview as the main data collection tool. The interview involved 14 respondents from Limpopo. The results showed marked gender difference in terms of roles performed. Based on the study, three kinds of roles were revealed: domestic, productive and decision-making roles. Men were significantly involved in productive roles, giving low priority to domestic roles. The key factors found to affect the role of women in decision-making in IWRM were cultural practices, low self-confidence, low levels of capacity, and high workloads. These factors were identified as key institutional inherent within the specific society. As such, these findings have significant implications for the efforts aimed at promoting gender equality. Particularly, the impact of culture on women in water management raises concerns regarding gender issues in rural and remote areas where people are poorer and more culturally conservative.     

The hyperpycnite problem

Sedimentologic, oceanographic, and hydraulic engineering publications on hyperpycnal flows claim that(1) river flows transform into turbidity currents at plunge points near the shoreline,(2) hyperpycnal flows have the power to erode the seafloor and cause submarine canyons, and,(3) hyperpycnal flows are efficient in transporting sand across the shelf and can deliver sediments into the deep sea for developing submarine fans. Importantly, these claims do have economic implications for the petroleum industry for predicting sandy reservoirs in deep-water petroleum exploration. However, these claims are based strictly on experimental or theoretical basis, without the supporting empirical data from modern depositional systems. Therefore, the primary purpose of this article is to rigorously evaluate the merits of these claims.A global evaluation of density plumes, based on 26 case studies(e.g., Yellow River, Yangtze River, Copper River,Hugli River(Ganges), Guadalquivir River, Rio de la Plata Estuary, Zambezi River, among others); suggests a complex variability in nature. Real-world examples show that density plumes(1) occur in six different environments(i.e., marine,lacustrine, estuarine, lagoon, bay, and reef);(2) are composed of six different compositional materials(e.g., siliciclastic,calciclastic, planktonic, etc.);(3) derive material from 11 different sources(e.g., river flood, tidal estuary, subglacial, etc.);(4) are subjected to 15 different external controls(e.g., tidal shear fronts, ocean currents, cyclones, tsunamis, etc.); and,(5) exhibit 24 configurations(e.g., lobate, coalescing, linear, swirly, U-Turn, anastomosing, etc.).Major problem areas are:(1) There are at least 16 types of hyperpycnal flows(e.g., density flow, underflow, high-density hyperpycnal plume, high-turbid mass flow, tide-modulated hyperpycnal flow, cyclone-induced hyperpycnal turbidity current, multi-layer hyperpycnal flows, etc.), without an underpinning principle of fluid dynamics.(2) The basic tenet that river currents transform into turbidity currents at plunge points near the shoreline is based on an experiment that used fresh tap water as a standing body. In attempting to understand all density plumes, such an experimental result is inapplicable to marine waters(sea or ocean) with a higher density due to salt content.(3) Published velocity measurements from the Yellow River mouth, a classic area, are of tidal currents, not of hyperpycnal flows. Importantly, the presence of tidal shear front at the Yellow River mouth limits seaward transport of sediments.(4) Despite its popularity, the hyperpycnite facies model has not been validated by laboratory experiments or by real-world empirical field data from modern settings.(5) The presence of an erosional surface within a single hyperpycnite depositional unit is antithetical to the basic principles of stratigraphy.(6) The hypothetical model of "extrabasinal turbidites", deposited by river-flood triggered hyperpycnal flows,is untenable. This is because high-density turbidity currents, which serve as the conceptual basis for the model, have never been documented in the world's oceans.(7) Although plant remains are considered a criterion for recognizing hyperpycnites, the "Type 1" shelf-incising canyons having heads with connection to a major river or estuarine system could serve as a conduit for transporting plant remains by other processes, such as tidal currents.(8) Genuine hyperpycnal flows are feeble and muddy by nature, and they are confined to the inner shelf in modern settings.(9) Distinguishing criteria of ancient hyperpycnites from turbidites or contourites are muddled.(10) After 65 years of research since Bates(AAPG Bulletin 37: 2119-2162, 1953), our understanding of hyperpycnal flows and their deposits is still incomplete and without clarity.     

黑河流域生态—水文过程综合遥感观测联合试验总体设计

介绍了"黑河流域生态—水文过程综合遥感观测联合试验"的背景、科学目标、试验组成和试验方案。试验的总体目标是显著提升对流域生态和水文过程的观测能力,建立国际领先的流域观测系统,提高遥感在流域生态—水文集成研究和水资源管理中的应用能力。由基础试验、专题试验、应用试验、产品与方法研究和信息系统组成。其中,①基础试验:搭载微波辐射计、成像光谱仪、热像仪、激光雷达等航空遥感设备,开展一系列关键生态和水文参量的观测;发展遥感正向模型及反演和估算方法。形成覆盖全流域的水文气象综合观测网,为流域生态—水文模型研究提供更有代表性的模型参数、驱动数据及更高精度的验证数据。构建无线传感器网络,度量生态水文模型所需的若干关键的驱动、参数和模型状态的空间异质性。开展航空遥感定标和地基遥感试验。依托传感器网络,并辅之以地面同步和加密观测,开展遥感产品真实性检验。②专题试验:开展"非均匀下垫面多尺度地表蒸散发观测试验",采用密集的涡动相关仪、大孔径闪烁仪与自动气象站的观测矩阵,为揭示地表蒸散发的空间异质性,实现非均匀下垫面地表蒸散发的尺度扩展,发展和验证蒸散发模型提供基础数据。③应用试验:在流域上、中、下游分别开展针对积雪和冻土水文、灌溉水平衡和作物生长、生态耗水的综合观测试验,将观测数据和遥感产品用于上游分布式水文模型、中游地表水—地下水—农作物生长耦合模型、下游生态耗水模型,通过实证研究提升遥感在流域生态—水文集成研究和水资源管理中的应用能力。加强试验将在2012年5月起按中游、上游、下游的顺序展开,全流域持续观测期为2013—2015年。在各类试验的支持下,开展全流域生态—水文关键参量遥感产品生产,发展尺度转换方法,建立多源遥感数据同化系统。     

Tier-based approaches for landslide susceptibility assessment in Europe

In the framework of the European Soil Thematic Strategy and the associated proposal of a Framework Directive on the protection and sustainable use of soil, landslides were recognised as a soil threat requiring specific strategies for priority area identification, spatial hazard assessment and management. This contribution outlines the general specifications for nested, Tier-based geographical landslide zonings at small spatial scales to identify priority areas susceptible to landslides (Tier 1) and to perform quantitative susceptibility evaluations within these (Tier 2). A heuristic, synoptic-scale Tier 1 assessment exploiting a reduced set of geoenvironmental factors derived from common pan-European data sources is proposed for the European Union and adjacent countries. Evaluation of the susceptibility estimate with national-level landslide inventory data suggests that a zonation of Europe according to, e.g. morphology and climate, and performing separate susceptibility assessments per zone could give more reliable results. To improve the Tier 1 assessment, a geomorphological terrain zoning and landslide typology differentiation are then applied for France. A multivariate landslide susceptibility assessment using additional information on landslide conditioning and triggering factors, together with a historical catalogue of landslides, is proposed for Tier 2 analysis. An approach is tested for priority areas in Italy using small administrative mapping units, allowing for relating socioeconomic census data with landslide susceptibility, which is mandatory for decision making regarding the adoption of landslide prevention and mitigation measures. The paper concludes with recommendations on further work to harmonise European landslide susceptibility assessments in the context of the European Soil Thematic Strategy.     

Using stratiform magnetic anomalies to map near-surface architecture: insights from the Amadeus Basin

The Amadeus Basin displays subtle magnetic anomalies that trace strata for considerable distance, highlighting complex folding patterns. Magnetic modelling techniques can be utilised on these stratiform anomalies to extrapolate the near-surface structure of the basin. However, because of the mathematical trade-off between the dip and magnetisation of bodies, the dips of the bodies cannot be known unless the magnetisation is also known. Normally it would be optimal to measure the magnetisation, but this is not always possible or feasible. In this study, we investigate the relationships between dip and magnetisation using an approach that would generally be considered a little backward, i.e. constraining magnetisation direction using geological data. Three study areas were chosen to investigate a number of stratigraphic horizons, the Waterhouse Range, Glen Helen and Ross River areas. Modelling results suggest that some layers primarily retain induced magnetisation, remanence is dominant in others, but both are present in most. Remanence is mainly associated with relatively oxidised units that contain only hematite (e.g. Arumbera Sandstone), and we have demonstrated that these magnetisations predate folding of the Ross River Syncline. In some cases, the anomalies represent redox zonation within units, e.g. the Pertatataka Formation near Glen Helen, where discrete magnetic layers correspond to thin grey (reduced, magnetite-rich) horizons interbedded with more prevalent red (oxidised, hematite-rich) horizons. We also found that where magnetised units are relatively thin and occur near the surface, their magnetic response is sharp, and in aeromagnetic data such adjacent anomalies commonly overlap to form a single anomaly, thus misrepresenting the magnetic field, and mis-mapping the actual magnetic horizons. While the magnetic properties of the causative bodies are variable, we have demonstrated that a better understanding of the magnetic properties of these magnetised horizons can be used to provide insights into the structure and tectonic history of the Amadeus Basin.     

An improved correlation model for sediment delivery ratio assessment

In the present work, a new simplified model approach for sediment delivery ratio (SDR) assessment is proposed. Modelling and assessing SDR is still an open question. Difficulties rise from the lack of sufficient data availability, on one side, and, on the other, from the inherent uncertainties including spatial variability and temporal discontinuity of the land cover, climatic, hydrological and geomorphological variables involved. The proposed SDR_SIM model tries to skip over the limitations observed in other models generally adopted. A comparison with two different selected models amongst the most widespread simplified models, i.e. the area-model and the slope-model, is showed in application to a wide range of catchments extensions across different landscapes of Italy. The SDR_SIM estimates were also evaluated against observed SDR over a validation dataset of 11 basins sparse over different regions of the world. The results showed the effectiveness of the proposed model approach based on easily available catchment parameters.     

大地电磁三维正演聚集多重网格算法

为了加快大地电磁三维正演的求解速度,本文将一种新型的代数多重网格算法——聚集多重网格（aggregation-based algebraic multigrid, AGMG）算法引入大地电磁三维正演模拟中。首先从准静态条件下的麦克斯韦方程出发,利用交错网格有限体积法进行离散,并采用第一类Dirichlet边界条件形成大型稀疏复线性方程组;然后阐述AGMG算法的粗化策略和套迭代技术,并实施3种不同的AGMG求解算法：1）传统的V循环AGMG算法;2）AGMG预处理共轭梯度（AGMG-CG）;3）AGMG预处理广义共轭残差法（AGMG-GCR）。最终实现大地电磁法三维正演模拟。对典型地电模型进行正演模拟,并与已有的大地电磁三维正反演程序（ModEM）进行结果对比,以验证本文算法的准确性。另外,不同剖分网格和极化方式正演模拟结果与准残量最小化（QMR）迭代算法的对比表明,AGMG预处理求解算法（AGMG-CG、AGMG-GCR）不仅能够改善算法的稳定性,而且能够快速有效地求解正演问题;其中AGMG-GCR迭代次数更少,求解速度更快,误差衰减曲线更光滑,在144×152×104网格剖分情况下,相对于现有ModEM程序能够提高十几倍的计算速度,尤其适合大规模大地电磁三维正演问题。