Intermittency analysis and spatial dependence of magnetic field disturbances in the fast solar wind

Based on Helios measurements, seven quantities of normalized PDF (Probability Distribution Function) associated with magnetic field and its disturbances are utilized to characterize the intermittency in the fast solar wind using Castaing distributions and the idea of “Flatness”. The magnetic field fluctuations are found to be more intermittent at farther distances from the sun. The “Flatness” decreases with increasing time scales, with the corresponding PDF eventually approaching Gaussian distributions. Such a transition occurs at a relatively small time scale for the perpendicular component of perturbed field. The increase in “Flatness” with decreasing time scale is more apparent farther from the sun. By examining how the relative energy density of magnetic disturbances at various time scales changes with the mean field, our study supports the idea that the perturbed fields in the fast solar wind in the frequency range considered are consistent with cross-scale redistribution of wave energy favoring larger scales.     

Optimal Estimation of Two-Dimensional Contaminant Transport

The state-space estimation technique presented herein provides a method for obtaining optimal estimates of concentrations for two-dimensional plumes in ground water. The concentration of a plume was defined as the state variable. The technique uses the Kalman filter and involves combining two independent estimates of plume concentrations. One estimate is called the process modeling data and the other is called the “measurement” data. The process modeling data is obtained from a numerical model. The “measurement” data is obtained from field measurements; however, for illustration in this paper it was generated by a different numerical model than the one used to obtain the process modeling data. The state-space technique produces a distribution of contaminant concentrations that is more accurate than either of the distributions generated by the process modeling or the “measurement” data. An example is presented to show that the technique produces significant improvements in the prediction of plume concentration distributions.     

Applying Higher Order DIRK Time Steps to the "Modified Picard" Method

The “modified Picard” iteration method, which offers global mass conservation, can also be described as a form of Newton's iteration with lagged nonlinear coefficients. It converges to a time step with first-order discretization error. This paper applies second- and third-order diagonally implicit Runge Kutta (DIRK) time steps to the modified Picard method in one example. It demonstrates improvements over the first-order time step in rms error and error-times-effort model quality by factors ranging from two to over two orders of magnitude, showing that the “modified Picard” and DIRK methods are compatible.     

A study on the discrete image method for calculation of transient electromagnetic fields in geological media

We conducted a study on the numerical calculation and response analysis of a transient electromagnetic field generated by a ground source in geological media. One solution method, the traditional discrete image method, involves complex operation, and its digital filtering algorithm requires a large number of calculations. To solve these problems, we proposed an improved discrete image method, where the following are realized: the real number of the electromagnetic field solution based on the Gaver–Stehfest algorithm for approximate inversion, the exponential approximation of the objective kernel function using the Prony method, the transient electromagnetic field according to discrete image theory, and closed-form solution of the approximate coefficients. To verify the method, we tentatively calculated the transient electromagnetic field in a homogeneous model and compared it with the results obtained from the Hankel transform digital filtering method. The results show that the method has considerable accuracy and good applicability. We then used this method to calculate the transient electromagnetic field generated by a ground magnetic dipole source in a typical geoelectric model and analyzed the horizontal component response of the induced magnetic field obtained from the “ground excitation–stratum measurement” method. We reached the conclusion that the horizontal component response of a transient field is related to the geoelectric structure, observation time, spatial location, and others. The horizontal component response of the induced magnetic field reflects the eddy current field distribution and its vertical gradient variation. During the detection of abnormal objects, positions with a zero or comparatively large offset were selected for the drillhole measurements or a comparatively long observation delay was adopted to reduce the influence of the ambient field on the survey results. The discrete image method and forward calculation results in this paper can be used as references for relevant research.     

The influence of channel morphology on bedload path lengths: Insights from a survival process model

Tracer studies are a commonly used tool to develop and test Einstein-type stochastic bedload transport models. The movements of these tracers are controlled by many factors including grain characteristics, hydrologic forcing, and channel morphology. Although the influence of these sediment storage zones related to morphological features (e.g., bars, pools, riffles) have long been observed to “trap” bedload particles in transport, this influence has not been adequately quantified. In this paper we explore the influence of channel morphology on particle travel distances through the development of a Bayesian survival process model. This model simulates particle path length distributions using a location-specific “trapping probability” parameter (p_i ), which is estimated using the starting and ending locations of bedload tracers. We test this model using a field tracer study from Halfmoon Creek, Colorado. We find that (1) the model is able to adequately recreate the observed multi-modal path length distributions, (2) particles tend to accumulate in trapping zones, especially during large floods, and (3) particles entrained near a trapping zone will travel a shorter distance than one that is further away. Particle starting positions can affect path lengths by as much as a factor of two, which we confirm by modelling “starting-location-specific” path length probability distributions. This study highlights the importance of considering both tracer locations and channel topography in examinations of field tracer studies. © 2020 John Wiley & Sons, Ltd.     

电离层层析重构的一种新算法

自适应联合迭代重构算法是电离层层析成像中一种收敛速度较快的反演算法.然而,在电离层电子密度重构过程中,该方法对迭代初值的精度要求较高.针对上述问题,本文提出了一种约束自适应联合迭代重构算法,该方法通过附加合理的平滑约束,减弱了没有观测信息的格网对迭代初值精度的依赖性,有效地提高了反演结果精度.数值模拟实验和实测数据的反演结果证实了该算法的可行性和在重构精度上的优越性.     

Cone-shaped source characteristics and inductance effect of transient electromagnetic method

Small multi-turn coil devices are used with the transient electromagnetic method (TEM) in areas with limited space, particularly in underground environments such as coal mines roadways and engineering tunnels, and for detecting shallow geological targets in environmental and engineering fields. However, the equipment involved has strong mutual inductance coupling, which causes a lengthy turn-offtime and a deep “blind zone”. This study proposes a new transmitter device with a conical-shape source and derives the radius formula of each coil and the mutual inductance coefficient of the cone. According to primary field characteristics, results of the two fields created, calculation of the conical-shaped source in a uniform medium using theoretical analysis, and a comparison of the inductance of the new device with that of the multi-turn coil, show that inductance of the multi-turn coil is nine times greater than that of the conical source with the same equivalent magnetic moment of 926.1 A·m². This indicates that the new source leads to a much shallower “blind zone.” Furthermore, increasing the bottom radius and turn of the cone creates a larger mutual inductance but increasing the cone height results in a lower mutual inductance. Using the superposition principle, the primary and secondary magnetic fields for a conical source in a homogeneous medium are calculated; results indicate that the magnetic behavior of the cone is the same as that of the multi-turn coils, but the transient responses of the secondary field and the total field are more stronger than those of the multi-turn coils. To study the transient response characteristics using a cone-shaped source in a layered earth, a numerical filtering algorithm is then developed using the fast Hankel transform and the improved cosine transform, again using the superposition principle. During development, an average apparent resistivity inverted from the induced electromotive force using each coil is defined to represent the comprehensive resistivity of the conical source. To verify the forward calculation method, the transient responses of H type models and KH type models are calculated, and data are inverted using a “smoke ring” inversion. The results of inversion have good agreement with original models and show that the forward calculation method is effective. The results of this study provide an option for solving the problem of a deep “blind zone” and also provide a theoretical indicator for further research.     

Assessing Water Quality of Mamasın Dam,Turkey: Using Water Quality Index Method,Ecological and Health Risk Assessments

The water quality of Mamas?n Dam, the drinking water source for Aksaray in Turkey, is investigated for assessment of ecological and health risks according to data between December 2015 and November 2016. Water quality index, ecological risk, and health risk assessments are determined to depend on the intensity of occurrence of parameters and seasonal and spatial distributions at different depth ranges. As a result, some ions such as Al, As, B, Ba, Co, F, Mn, Ni, Pb, Se, and Zn were found to be exceeding the limit values of the national regulatory standards. Besides, Pb is listed in Priority Substances and Certain Other Pollutants according to Annex II. Because the WQI values of the water quality are low (below 60), the source is suitable for industrial and agricultural usage; however, it cannot be used for drinking water supply without treatment. The trace element levels, especially Ag, Ba, Cu, Cr, and Zn, are potential pollutants for organisms. The non‐carcinogenic health risks of As threaten both adults and children at “medium” and “high” levels through oral ingestion. The B, F, and Pb elements have Hazard Index values above 0.1 and may cause a “low” level risk chronic disease for children by oral ingestion.     

Analysis of the geomagnetic induction tensor

The geomagnetic induction tensor is a means of summarizing the response of the earth at a given observing site to a geomagnetic variation source field. In this paper the characteristics of the tensor elements are examined, both generally and for the special cases of one-dimensional and two-dimensional geologic structure. The first-order model is taken of uniform source fields originating external to a semi-infinite half-space. Graphical ways of presenting the information contained in an induction tensor are explored, including ellipses of rotation, polar diagrams, and diagrams analogous to the Mohr circles of elasticity theory. Criteria to distinguish “two-dimensional” data from “three-dimensional” data are established. The advantages of simultaneously recording “normal” and “anomalous” variations are demonstrated in terms of the extra tensor elements which may then be estimated. The most practical way of presenting information from many stations on a map may be by drawing, for each site, arrows which summarize the response in the vertical field and quadrics which summarize the response in the horizontal field.     

Abrasion in pyroclastic density currents: Insights from tumbling experiments

During granular mass movements of any kind, particles may interact with one another. The degree of interaction is a function of several variables including; grain-size distribution, particle concentration, density stratification and degree of fluidisation. The impact of particle interaction is additionally influenced by the relative speed, impact angle and clast temperature. Thus, both source conditions and transport-related processes are expected to influence the flow dynamics of pyroclastic density currents and their subsequent deposition. Here, we use tumbling experiments to shed light on the susceptibility of porous clasts to abrasion.We investigated the abrasion of unaltered volcanic rocks (5.7–80 vol.% porosity) from Unzen (Japan), Bezymianny (Russia) and Santorini (Greece) volcanoes as well as one synthetic analogue material, an insulating material with the trade name Foamglas® (95 vol.% porosity). Each experiment started with angular fragments generated in a jaw crusher from larger clasts. Two experimental series were performed; on samples with narrow and broader grain-size distributions, respectively. The dry samples were subject to rotational movement at constant speed and ambient temperature in a gum rotational tumbler for durations of 15, 30, 45, 60 and 120 min. The amount of volcanic ash (particles <2 mm) generated was evaluated as a function of experimental duration and sample porosity. We term “abrasion” as the ash fraction generated during the experiments.The observed increase of “abrasion” with increasing sample porosity and experimental duration is initially non-linear but becomes linear for experiments of 30 min duration or longer. For any given sample, abrasion appears to be more effective for coarser samples and larger initial mass. The observed range of ash generated in our experiments is between 1 and 35 wt.%. We find that this amount generally increases with increasing initial clast size or increasing breadth of the initial grain-size distribution.Despite the limits in the complexity that is experimentally attainable in this simulation of ash generation, our results clearly testify the rapid and efficient generation of ash by abrasion, strongly influenced by the material properties (e.g., crystallinity, pore textures).     

迭代法与FFT法位场向下延拓效果的比较

将水平观测面上的实测位场值,垂直投影至下部的延拓水平面上,作为该水平面上的位场初始值. 根据该水平面上的初始值,用快速傅里叶变换(FFT)的方法向上延拓计算观测面上的位场值. 用观测面上的实测值与计算值的差值,对延拓面上的位场值进行校正. 如此反复迭代,直至观测面上的实测值与计算值的差值小到可以忽略. 这种空间域的迭代法原理简单,不用解线性代数方程组,有较高的计算速度和良好的延拓效果. 本文用迭代法对模型数据和实际数据进行向下延拓,对比了迭代法与常规的FFT法在位场向下延拓中的效果,迭代法显著优于FFT法.     

松辽盆地北部布格重力异常场源分布

基于不同场源频谱成分的不同,研究松辽盆地北部布格重力异常的场源分布特征。利用匹配滤波方法计算松辽盆地北部布格重力异常的不同场源平均深度,将其分为浅源场、中源场和深源场,并推测松辽盆地北部的地壳有3层结构。浅源场产生的重力异常大,对重力勘探贡献最大;中源场和深源场的重力异常都比较小,但两者有极好的继承性。有了场源的平均深度,利用Parker迭代反演法计算上地壳与中地壳之间的界面起伏,在该界面上可看到松辽盆地北部的“隆起区-沉积盆地-隆起区”的构造特征。     

Handbuch der Physik-Geophysik III/6: G.M. Von Nikol'skij,K. Rawer,P. Stubbe,L. Thomas and T. Yonezawa. Springer-Verlag, 1982, 124 Figs., VI + 385 pp., US $126.60, ISBN 3-540-07080-X

A model mechanism has been derived for the evolution of the cation distribution in titanomaghemites, which have formed by the progressive removal of iron from the spinel lattice. According to the model, the cation distribution of a titanomaghemite is not a unique function of composition but depends on the path by which maghemitization has taken place. Cation distributions (and consequent magnetic properties) have been calculated and compared for titanomaghemite produced by the “removal of iron” and “addition of oxygen” mechanisms. For a given composition, the Curie point temperature is almost invariant, being, according to molecular field theory, more sensitive to composition than cation distribution. Therefore, the model cannot explain the variations observed in synthetic titanomaghemite of different provenances. According to the model, the spontaneous magnetization is significantly lower for the removal of iron mechanism, which may be helpful in explaining a decrease in the remanence of submarine basalts with age.Structurally metastable titanomaghemites invert to an intergrowth of phases on heating above approximately 350°C and it is expected that the inversion product would be independent of the mechanism by which maghemitization had previously taken place. Available X-ray, and other data, have been used to produce a simple model of the inversion process, and values of the Curie point of the inversion product and the ratio of the magnetization before and after the inversion derived. These model values compare favourably with experimental values for a synthetic titanomaghemite in which inversion was induced by progressive slow heating to approximately 600°C. The inversion process therefore has potential in determining the compositions of naturally occurring titanomaghemites.     

An approximate least squares reflectivity inversion in the presence of density

Traditional least-squares reverse time migration (LSRTM) often aims to improve the quality of seismic imaging, such as removing the acquisition footprint, suppressing migration artifacts and enhancing resolution. In this paper, we find that the conventional reflectivity defined in the LSRTM is related to the normal-incident reflection coefficient and the background velocity. Compared with the defined reflectivity, our inverted result is relatively “true”. With reflected data, LSRTM is mainly sensitive to impedance perturbations. According to an approximate relationship between them, we reformulate the perturbation related system into a reflection-coefficient related one. Then, we seek the inverted image through linearized iteration. Moreover, with the assumption that the density varies more gradually than the migration velocity, only the knowledge of the latter is required, although the reflected waves are produced at impedance discontinuities. We test our method using the 2D Marmousi synthetic dataset.     

BOUNDARY ELEMENT METHOD FOR THE ARBITRARY INHOMOGENEITIES PROBLEM IN ELECTRICAL PROSPECTING*

The generalized integral equation for the electric potential governed by a quasi-harmonic equation can be derived via a variational formulation. For surface current distributions it is not always a Fredholm integral equation of the second kind. Numerical solutions of the general heterogeneous problem can be obtained with the “reciprocal averaging technique”, where the solution is obtained a second time after exchange of source and field points.     

Assessment of heavy metal pollution in Xuzhou urban topsoils by magnetic susceptibility measurements

The concentrations of four selected heavy metals (Pb, Zn, Ni and Cr) were measured on 167 topsoil samples collected from the city of Xuzhou, China via inductively coupled plasma mass spectroscopy (ICP-MS). It was found that Pb and Zn were principally derived from anthropogenic inputs whereas Cr and Ni distributions were mainly controlled by parent materials. The spatial distribution patterns of Pb, and Zn were similar to that from low field magnetic susceptibility (χlf), suggesting interaction among them. Two threshold values for magnetic susceptibility and frequency-dependent susceptibility percentage (χfd) were applied to discriminate between polluted and unpolluted samples according to their magnetic susceptibility, resulting in 109 samples populating the “polluted” subset. The Pb and Zn concentrations of the “polluted” subset were statistically significantly higher than those measured in the “unpolluted” one. The heavy metal concentrations were also investigated varying the magnetic susceptibility thresholds to change the “polluted” subset.     

Towards an accurate real-time locator of infrasonic sources

Infrasonic signals propagate from an atmospheric source via media with stochastic and fast space-varying conditions. Hence, their travel time, the amplitude at sensor recordings and even manifestation in the so-called “shadow zones” are random. Therefore, the traditional least-squares technique for locating infrasonic sources is often not effective, and the problem for the best solution must be formulated in probabilistic terms. Recently, a series of papers has been published about Bayesian Infrasonic Source Localization (BISL) method based on the computation of the posterior probability density function (PPDF) of the source location, as a convolution of a priori probability distribution function (APDF) of the propagation model parameters with likelihood function (LF) of observations. The present study is devoted to the further development of BISL for higher accuracy and stability of the source location results and decreasing of computational load. We critically analyse previous algorithms and propose several new ones. First of all, we describe the general PPDF formulation and demonstrate that this relatively slow algorithm might be among the most accurate algorithms, provided the adequate APDF and LF are used. Then, we suggest using summation instead of integration in a general PPDF calculation for increased robustness, but this leads us to the 3D space-time optimization problem. Two different forms of APDF approximation are considered and applied for the PPDF calculation in our study. One of them is previously suggested, but not yet properly used is the so-called “celerity-range histograms” (CRHs). Another is the outcome from previous findings of linear mean travel time for the four first infrasonic phases in the overlapping consecutive distance ranges. This stochastic model is extended here to the regional distance of 1000 km, and the APDF introduced is the probabilistic form of the junction between this travel time model and range-dependent probability distributions of the phase arrival time picks. To illustrate the improvements in both computation time and location accuracy achieved, we compare location results for the new algorithms, previously published BISL-type algorithms and the least-squares location technique. This comparison is provided via a case study of different typical spatial data distributions and statistical experiment using the database of 36 ground-truth explosions from the Utah Test and Training Range (UTTR) recorded during the US summer season at USArray transportable seismic stations when they were near the site between 2006 and 2008.     

Depth determination from a non-stationary magnetic profile for scaling geology

The conventional spectral analysis method for interpretation of magnetic data assumes stationary spatial series and a white‐noise source distribution. However, long magnetic profiles may not be stationary in nature and source distributions are not white. Long non‐stationary magnetic profiles can be divided into stationary subprofiles following Wiener filter theory. A least‐squares inverse method is used to calculate the scaling exponents and depth values of magnetic interfaces from the power spectrum. The applicability of this approach is demonstrated on non‐stationary synthetic and field magnetic data collected along the Nagaur–Jhalawar transect, western India. The stationarity of the whole profile and the subprofiles of the synthetic and field data is tested. The variation of the mean and standard deviations of the subprofiles is significantly reduced compared with the whole profile. The depth values found from the synthetic model are in close agreement with the assumed depth values, whereas for the field data these are in close agreement with estimates from seismic, magnetotelluric and gravity data.     

Modeled Ground Water Age Distributions

The age of ground water in any given sample is a distributed quantity representing distributed provenance (in space and time) of the water. Conventional analysis of tracers such as unstable isotopes or anthropogenic chemical species gives discrete or binary measures of the presence of water of a given age. Modeled ground water age distributions provide a continuous measure of contributions from different recharge sources to aquifers. A numerical solution of the ground water age equation of Ginn (1999) was tested both on a hypothetical simplified one‐dimensional flow system and under real world conditions. Results from these simulations yield the first continuous distributions of ground water age using this model. Complete age distributions as a function of one and two space dimensions were obtained from both numerical experiments. Simulations in the test problem produced mean ages that were consistent with the expected value at the end of the model domain for all dispersivity values tested, although the mean ages for the two highest dispersivity values deviated slightly from the expected value. Mean ages in the dispersionless case also were consistent with the expected mean ages throughout the physical model domain. Simulations under real world conditions for three dispersivity values resulted in decreasing mean age with increasing dispersivity. This likely is a consequence of an edge effect. However, simulations for all three dispersivity values tested were mass balanced and stable demonstrating that the solution of the ground water age equation can provide estimates of water mass density distributions over age under real world conditions.