Formation of complex rotational structures in convective and isothermal magnetized zones

We study the development of a complex rotation law in the magnetized convective and isothermal zones of stars and planetary atmospheres through the decomposition of vector quantities in terms of orthogonal vector spherical harmonics. In the case of a solar-type extended convective zone, it is assumed that (a) the transformation of thermal into magnetic energy is favorable from the viewpoint of energy balance, (b) the state that is supported with minimum energy loss is realized, and (c) the condition of minimum entropy production consistent with the two previous requirements is satisfied. To find the rotation law of a zone, weak interaction between variations in the rotation and magnetic-field distributions is assumed. Two possible zones of generation of the solar magnetic field are considered. The first is located in the lower half of the solar convective zone and possesses a latitude dependence of the rotational velocity similar to that observed. The second zone is located just below the surface, and has a rotational velocity that decreases sharply with height and depends only weakly on latitude. We also study simple equilibrium structures, in particular, those describing the super-rotation of the medium in a convective or isothermal zone. Realization of such super-rotation in an isothermal zone is associated with the outflow of matter and fields toward upper layers.     

The solar dynamo and integrated irradiance variations in the course of the 11-year cycle

Abstractthe effect of the large-scale magnetic fields generated by the solar dynamo on the radiation flux issuing from the convection zone is studied. A governing equation describing convective heat transfer is obtained in the framework of mean-field magnetohydrodynamics, with account for the influence of magnetic fields and differential rotation on the energy budget of the convection zone. The principal effects are illustrated using a one-dimensional numerical model. Calculations indicate that the influence of large-scale magnetic fields can modulate the solar irradiance with a relative amplitude of ～0.07%.     

Magnetic fields in the radiative-transport zone and the solar cycle

It is shown that a hypothetical relict magnetic field in the solar radiative-transport zone that penetrates into the convective zone would affect the solar dynamo, resulting in radical changes in the butterfly diagrams. This would transform the traveling waves of activity into standing waves. A comparison of our results with the well-known butterfly diagrams for the Sun gives an upper limit of the order of some tens G for the value of relict magnetic field penetrating into the solar convective zone. At the same time, it is not ruled out that such relict magnetic fields in other solar-type stars are strong enough to make the activity waves become standing waves.     

Evolution of solar magnetic tubes from observations of Stokes parameters

Basic scenarios and mechanisms for the formation and decay of small-scale magnetic elements and their manifestation in synthesized Stokes profiles of the Fe I 15648.5 Å infrared line are considered in the context of two-dimensional modeling of nonstationary magnetogranulation on the Sun. The stage of convective collapse is characterized by large redshifts in the V profiles accompanied by complete Zeeman splitting of the I profiles. This is due to intense downward flows of material, which facilitates the concentration of longitudinal field with an amplitude of about several kG in the tube. The dissipation of strong magnetic structures is characterized by blueshifts in their profiles, which result from upward fluxes that decrease the magnetic field in the tube. Typical signatures during key stages in the evolution of compact magnetic elements should be detectable via observations with sufficiently high spatial and temporal resolution.     

Palaeomagnetism applied to magnetic anomaly interpretation: a new twist to the search for mineralisation in northern Chile

The Chilean Iron Belt is an important location for Fe and Cu(Fe)-Au deposits and includes the recently developed Candelaria deposit, which is located some 20 km south of the city of Copiapó in northern Chile. This mine is now a major Cu producer in Chile but its discovery in the late 1980s was relatively fortuitous. The exploration programme included a ground magnetic survey from which lessons can be learnt in the search for further such deposits. Palaeomagnetic studies throughout the northern part of the Chilean Iron Belt indicate major crustal rotation of the region, probably, related to oblique convergence and transpression at the Andean Margin. The application of palaeomagnetic techniques to a magnetite-apatite deposit, Mina Fresia, indicates that magnetite-rich ores in this area are capable of maintaining a significant remanence component which will contribute to their magnetic anomaly. As with the volcanics, intrusives and sediments of the region this, remanence is clearly rotated clockwise. Using 2.5D and 3D magnetic modelling, it is demonstrated that the magnetic anomaly associated with the Candelaria deposit is also dominated by a remanence component which is significantly rotated but of reversed polarity. Recognition of clockwise-rotated, remanence-dominated anomalies should provide a new key to the search for deposits in this part of Chile and elsewhere. An example of an unexplored anomaly showing this key feature of a clockwise-rotated remanence component dominating over the induced component is presented. Modelling of this anomaly indicates a pair of sources which are either ten times as big or ten times as magnetic as the Candelaria deposit. It is suggested that the low cost of palaeomagnetic study of an exploration target should be a prerequisite to magnetic anomaly interpretation of targets in tectonic areas where vertical axis crustal rotations may be a significant element of the overall deformation pattern. Received: 9 April 1999 / Accepted: 5 October 1999     

Near-polar starspots and polar dynamo waves

A possible mechanism for the formation of near-polar magnetic spots on some stars with convective envelopes is proposed. The mechanism is based on the idea that the maximum of the dynamo waves that are excited in thin convective shells by the dynamo mechanism is shifted appreciably from the maximum of the magnetic-field sources in the direction of motion of the dynamo wave. If there is no region of super-rotation near the equator for some reason (as a consequence of disruption due to tidal interaction with a companion in a binary system, for example) and the wave of stellar activity propagates toward the poles rather than toward the equator, this maximum will be in the near-polar regions.     

Possible scenarios for the formation of Ap/Bp stars

Possible paths for the formation of Ap/Bp stars—massive main-sequence stars with strong magnetic fields—are analyzed based on modern theories for the evolution of single and binary stars. Assuming that the strong magnetic fields of these stars are the main reason for their comparatively slow axial rotation and the observed anomalies in the chemical compositions of their atmospheres, possible origins for these high magnetic fields are considered. Analysis of several possible scenarios for the formation of these stars leads to the conclusion that their surface magnetic fields are probably generated in the convective envelopes of the precursor stars. These precursors may be young, single stars with masses 1.5–3 M _⊙ that formed at the peripheries of forming star clusters and ended their accretion at the Hayashi boundary, or alternatively close binaries whose components have convective envelopes, whose merger leads to the formation of an Ap/Bp star. Arguments are presented supporting the view that the merger of close binaries is the main channel for the formation of Ap/Bp stars, and a detailed analysis of this scenario is presented. The initial major axes of the merging binary systems must be in the range 6–12 R _⊙, and the masses of their components in the range 0.7–1.5 M _⊙. When the merging components possess developed convective envelopes and fairly strong initial magnetic fields, these can generate powerful magnetic fields “inherited” by the products of the merger—Ap/Bp stars. The reason the components of the close binaries merge is a loss of angular momentum via the magnetic stellar winds of the components.     

Magnetohydrodynamic model of the solar tachocline

The tachocline is a thin layer providing the transition from differential to uniform rotation in the upper region of the solar radiative zone, which can be explained as an effect of the magnetic field if the magnetic field lines are closed inside the radiative zone. It is shown that the confined field structure that is necessary for the tachocline formation can arise due to the penetration of meridional flow from the convective envelope to the radiative zone. The time for the distortion of the magnetic field by the penetrating flow is short compared to the time for diffusion to the penetration depth. The most long-lived mode of the poloidal field has a confined geometry, and the Ohmic lifetime of this mode exceeds the age of the Sun. The calculated distribution of the angular velocity in the radiative zone taking into account such a field shows a thin tachocline.     

Convective mechanism for the formation of photospheric magnetic fields

The well-known model that attributes the formation of a bipolar sunspot group to the emergence of a flux tube disagrees sharply with the usual observed pattern of phenomena. At the same time, the observed patterns can be accounted for quite convincingly in terms of local magnetic-field amplification due to cellular convective motions of the solar plasma. In this study, magnetoconvection in a plane horizontal fluid layer is simulated numerically in the framework of the fully nonlinear, three-dimensional problem. A weak horizontal magnetic field and weak cellular flow are assumed to be present initially. Convection is shown to be capable of producing bipolar magnetic configurations of the strongly amplified magnetic field. Indications of magnetic freezing of the flow in the cell are found. The action of the amplification mechanism under study may be controlled by the large-scale toroidal magnetic field of the Sun.     

定向扫描成像测井技术及其应用

定向扫描成像测井技术，就是按照规定的方向对井壁进行扫描，把井壁展开成一个连续的平面。这种信号不能在磁屏蔽、磁干扰条件下工作，进而不能确定地质信息的方位。然而，当运用陀螺定向技术对人造磁场进行定向，在人造磁场中，转动的线圈感应出来的交变电信号作为图像扫描触发信号，能够测量所形成的超声图像，并快捷、准确地查明井管故障点的位置、损坏的规模大小和方位，从而为维修方案的确定提供了可靠的依据。     

Using naive Bayes classifier for classification of convective rainfall intensities based on spectral characteristics retrieved from SEVIRI

This paper presents a new algorithm to classify convective clouds and determine their intensity, based on cloud physical properties retrieved from the Spinning Enhanced Visible and Infrared Imager (SEVIRI). The convective rainfall events at 15 min, 4 × 5 km spatial resolution from 2006 to 2012 are analysed over northern Algeria. The convective rain classification methodology makes use of the relationship between cloud spectral characteristics and cloud physical properties such as cloud water path (CWP), cloud phase (CP) and cloud top height (CTH). For this classification, a statistical method based on ‘naive Bayes classifier’ is applied. This is a simple probabilistic classifier based on applying ‘Bayes’ theorem with strong (naive) independent assumptions. For a 9-month period, the ability of SEVIRI to classify the rainfall intensity in the convective clouds is evaluated using weather radar over the northern Algeria. The results indicate an encouraging performance of the new algorithm for intensity differentiation of convective clouds using SEVIRI data.     

Horizontal magnetic fields in the solar photosphere

Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields and the response of the synthesized Stokes profiles of the IR FeI λ1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic network in the photosphere with an unsigned magnetic flux density of 192 G at the solar surface. According to the magnetic-field distribution obtained, the most probable absolute strength of the horizontal magnetic field at an optical depth of τ ₅ = 1(τ ₅ denotes τ at λ = 500 nm) is 50 G, while the mean value is 244 G. On average, the horizontal magnetic fields are stronger than the vertical fields to heights of about 400 km in the photosphere due to their higher density and the larger area they occupy. The maximum factor by which the horizontal fields are greater is 1.5. Strong horizontal magnetic flux tubes emerge at the surface as spots with field strengths of more than 500 G. These are smaller than granules in size, and have lifetimes of 3–6 min. They form in the photosphere due to the expulsion of magnetic fields by convective flows coming from deep subphotospheric layers. The data obtained qualitatively agree with observations with the Hinode space observatory.     

Current-independent paleomagnetic declinations in flysch basins: a case study from the Inner Carpathians

Paleomagnetic declinations from the Inner Carpathian Paleogene Basin imply that the area rotated counterclockwise about 60°, during the Miocene[1]. The question may arise if the paleomagnetic declination could have been biased by the W-E directed turbidity currents prevailing in the basin causing an apparent counter-clockwise rotation of the paleomagnetic direction.

The paleomagnetic results were obtained for fine grained strata, deposited in relatively calm water. Nevertheless, to confirm the paleomagnetic rotation, we needed evidence that flow activity on the magnetic grains was indeed insignificant in the beds yielding paleomagnetic results. Therefore, we carried out magnetic anisotropy measurements.

Results of AMS (representing para and ferromagnetic minerals together) measurements, compared with paleomagnetic observations, demonstrate that well-clustered lineations at locality level and failure to define a paleomagnetic direction are coupled. Lineation, when observable, is flow parallel, suggesting that magnetic lineation in the Inner Carpathian flysch basins may be regarded as a good proxy for turbidity current direction. It is remarkable, however, that the well-defined paleomagnetic directions are observed for localities, where the magnetic fabric is not showing lineation on locality level. Moreover, the lineation direction of the ferromagnetic minerals alone (obtained by measuring the anisotropy of the remanence) is independent of that of the turbidity currents. Thus we can safely conclude that the Inner Carpathian flysch basin indeed was affected by 60° tectonic rotation, and the paleomagnetic vectors were not biased by paleocurrents.     

An evaluation of slump fold formation using palaeomagnetic techniques

Distorted bedding and soft-sedimentary deformation structures are abundant at the base of the Late Miocene Pannonian sequence, due to rapid basin subsidence and high sedimentary input. A well-preserved slump fold was observed at a depth of 1341 m in Iharosberény I. core hole, SW Hungary. Detailed palaeomagnetic analysis of this fold indicated that the magnetic grains rotated to a certain degree during folding, but the rock has not been remagnetized during and after folding. It is concluded that remanent magnetization was acquired soon after deposition and before folding.     

白银厂矿区劈理成因的磁组构分析

将磁性组构方法用于甘肃白银厂矿区的构造分析.结果表明该区岩石的磁性组构与岩石组构具有同一分布规律.岩石的磁线理与岩石的拉长线理L~a近于一致,磁面理与第一期劈理S_1基本平行,并垂直于岩石的磁化率椭球的最小主轴,也垂直于应变椭球的最短主轴方位,故推断第一期劈理S_1的成因主要属压扁成因.同时受到后期的多次变形与褶皱迭加影响.S_1轴面的优选面状分布发生变位不大,表明该区多次构造变形主要来自早期的同一主应力场作用所致.矿区岩石的磁面理与应变椭球拉长轴面或第一期劈理面S_1存在某些的角度差,表明该区岩石的劈理面由于受后期多次构造变形影响,可能发生剪切运动或旋转机制.     

Mantle sources of the Cenozoic volcanic rocks of East Asia: Derivatives of slabs,the sublithospheric convection,and the lithosphere

The spatial-temporal variations of the trace element and Sr isotope composition were analyzed in the Middle-Late Cenozoic volcanic rocks of the East Asian continental margin. The heterogeneity of the sublithospheric mantle was characterized, the active sources of the supraslab mantle were distinguished, and the Southern and Northern sublithospheric convective subdomains of the Transbaikalian low-velocity domain at a depth of 410–200 km were distinguished. The supply of isotopically homogenous mantle from the convective subdomains was replaced in space and time by their mixtures. Isotopically highly depleted material was derived from the mantle above the Kula-Izanagi and Pacific slabs ～43.5, 23–17, and <15 Ma, while moderately depleted mantle was derived from the Northern and Southern subdomains ～37, 31–23, and ～16 Ma and 19–12 Ma, respectively. Similar convective but shallower isotopically enriched material was determined in mixtures from the Southern convective subdomain in the Northeast Japanese arc within 30–9 Ma and in mixtures with isotopically enriched lithospheric mantle in the central Heilongjiang Province <9.6 Ma. Lithospheric melts erupted during drastic changes in the dynamics of the sublithospheric convective subdomains.     

The magnetic-field structures of chemically peculiar stars

Measurements of the longitudinal magnetic field of the CP star HD 62140 with high accuracy (σ ～ 50 G) are used to construct a magnetic-dipole model for this star. The model describes the observed phase dependence of the field very well, supporting the idea that CP stars have dipolar magnetic fields. Based on an analysis of the CP stars HD 32633 and HD 142301, which were earlier suggested to have dipoles shifted perpendicular to the dipole axis, it is concluded that the only possible models in this case have one or two shifted dipoles, with the distance between the monopoles being comparable to the stellar radius. Such configurations may occur as a consequence of deformations of the field in early stages of the star’s evolution, due to the accretion of higher-mass objects or a merger with another component, as well as the influence of a convective core.     

The Fokker-Planck equation and statistical characteristics of penetrative convection in the upper ocean

We consider the problem of penetrative convection in the upper ocean under the conditions of sharp surface cooling and a constant momentum flux connected with the existing system of random waves. The Langevin equation with a random right part is used to describe a convective ensemble of thermals. The kinetic Fokker-Planck equation is built for the angular probability density of an ensemble of convective elements. The stationary solution of this equation allows one to find an analogue of the Boltzman distribution for convective currents over speed and height. The Maxwell speed distribution is implemented in this case for convective thermals at a fixed depth. The results allow interpretation of certain data on turbulence in the convective near-surface ocean layer.     

花岗岩粗糙单裂隙对流换热特性的数值模拟

在干热岩储层中开采地热能,往往需要对储层进行人工水力压裂以形成贯穿的换热通道。然而,热储中的对流换热对干热岩的采热率有重要影响,经过人工刺激的储层会形成几何形态各异的裂隙面,而裂隙粗糙程度的不同则会引起换热性能的显著差异。因此,选取4条Barton的经典岩石裂隙粗糙度曲线,在试验室条件下建立一个单裂隙对流换热模型。详细分析了花岗岩粗糙裂隙中热工质的换热特性。结果表明：局部对流换热系数沿着裂隙长度方向逐渐降低;节理粗糙系数JRC值越大,平均对流换热系数就越大,表明换热性能越好;局部对流换热系数的分布与JRC曲线的几何轮廓形态有很好的相关性,波峰波谷的变化趋势相一致;相对于温度而言,高流速对局部对流换热系数具有放大效应,流速越大,局部对流换热系数波动越大。     

Double Diffusion-Driven Convective Instability of Three-Dimensional Fluid-Saturated Geological Fault Zones Heated from Below

We conduct a theoretical analysis to investigate the double diffusion-driven convective instability of three-dimensional fluid-saturated geological fault zones when they are heated uniformly from below. The fault zone is assumed to be more permeable than its surrounding rocks. In particular, we have derived exact analytical solutions to the total critical Rayleigh numbers of the double diffusion-driven convective flow. Using the corresponding total critical Rayleigh numbers, the double diffusion-driven convective instability of a fluid-saturated three-dimensional geological fault zone system has been investigated. The related theoretical analysis demonstrates that: (1) The relative higher concentration of the chemical species at the top of the three-dimensional geological fault zone system can destabilize the convective flow of the system, while the relative lower concentration of the chemical species at the top of the three-dimensional geological fault zone system can stabilize the convective flow of the system. (2) The double diffusion-driven convective flow modes of the three-dimensional geological fault zone system are very close each other and therefore, the system may have the similar chance to pick up different double diffusion-driven convective flow modes, especially in the case of the fault thickness to height ratio approaching 0. (3) The significant influence of the chemical species diffusion on the convective instability of the three-dimensional geological fault zone system implies that the seawater intrusion into the surface of the Earth is a potential mechanism to trigger the convective flow in the shallow three-dimensional geological fault zone system.