Observational connection between local high-temperature phenomena within magnetic clouds and the Sun

Magnetic clouds (MCs) frequently show abnormal high-ionization states of heavy ions. The abnormal high-charge distributions are related to the coronal temperature of their source regions. We examined the plasma and magnetic field data of 74 MCs observed by the Advanced Composition Explorer from February 1998 to December 2008. We determined that 14 of the 74 events showed local high-temperature phenomena. We analyzed the correlation between proton temperature and O⁷/O⁶ ratio (or high mean Fe charge state 〈Fe〉) within the local high-temperature regions in the 14 MCs. Results show that proton temperature and O⁷/O⁶ ratio (or high mean Fe charge state) had good correlations in nine MCs, but had no evident correlation in the other five MCs. The local high-temperature phenomena within the nine MCs have resulted from the Sun.     

磁场重联中的电子加速机制的数值模拟研究

在应用2.5维混合模拟方法研究Petschek模型磁场重联的基础上,考察了试验电子被加速的特征. 模拟结果表明,稳态的低频重联场能将少量试验电子加速到高能,电子的能谱为幂律谱,但总体分布函数未发生显著变化. 电子在整个加速过程中被束缚在低磁场的加速区内,由重联产生的感应电场Ey分量对其直接加速,根据加速时间和加速区域可以将这些电子分为两种情况：初始位于加速区和漂移到加速区被加速.     

磁场重联中电子加速问题的物理分析和数值研究

观测表明耀斑中电子加速发生在软X射线耀斑环上方的磁重联区域.在重联电流片中被super-Dreicer电场直接加速似乎是产生能量在10keV～10MeV之间高能电子的最直接的方式.本文的结果证明纵向电磁场可以有效地将电子“锁”在重联电流片上,使得横向电场得以直接加速电子.对于解释产生相对论性粒子的脉冲式耀斑,这可能是一个有效的机制.     

Steep latitudinal gradients of thermospheric composition during magnetic storms: a possible formation mechanism

Mass spectrometer satellite observations show that a narrow region with steep latitudinal gradients of neutral composition is formed in the subauroral winter thermosphere during magnetic storms. In order to analyze the relative importance of individual terms in the continuity equation for atomic oxygen, a two-dimensional model was used to simulate the thermospheric disturbance formation in response to intense Joule heating imposed in the auroral oval. Such an approach allowed three characteristic zones to be distinguished in the high-latitude thermosphere at heights of about 250 km. It was shown that vertical transport is of greatest importance within the local heating region. Horizontal transport dominates at subauroral latitudes near the mid-night edge of the auroral oval. Propagation of the disturbances to middle latitudes is prohibited near the noon edge of the oval by a strong counteraction of a poleward meridional wind. Here is a “relaxation zone” defined as the region which is spread to the equator from the boundary between the local heating area and the subauroral zone in the noon sector LT. It is at this boundary that composition distributions with steep latitudinal gradient are formed within the first few hours of Joule heating source action. Perturbations transported to middle latitudes during the periods when the meridional wind is directed equatorward begin to relax in this zone with a characteristic time scale of about 7 h, independent of season. However, in winter, composition at subauroral latitudes recovers to unperturbed N₂/O values before the wind again turns equatorward, giving rise to a distribution with steep latitudinal gradient recovering. In summer, a complete relaxation cannot be reached due to a shorter time interval with poleward wind and a larger disturbance amplitude. These two factors result in an effective smoothing of the initial steep gradient and a more regular latitudinal distribution of composition is observed in the summer thermosphere.     

IMF北向时磁层顶重联的模拟研究

本文基于自己开发的全球三维磁层模型,模拟研究了IMF(Interplanetary Magnetic Field)北向时磁层顶重联及磁尾结构.结果发现磁层顶附近存在两种典型的重联过程:一是高纬极尖区IMF与地球磁场的重联,这与空间观测证据和前人的模拟结果是一致的;二是重联后一端在太阳风中另一端与地球相连的磁力线在向磁尾运动中,会发生弯曲、拖曳,在磁尾晨昏侧低纬区域可与尾瓣开放磁力线满足重联条件而再次发生重联.我们认为前一重联会使磁尾等离子片产生与IMF时钟角方向相反的旋转;而后者可重新形成闭合磁力线,可能是LLBL(Low Latitude Boundary Layer)形成的重要原因.     

模拟IMF北向且By分量占主导时磁层顶重联

本文基于自己开发的全球三维磁层模型, 模拟研究了IMF(Interplanetary Magnetic Field)北向并且B_y分量较大(时钟角为60°)时磁层顶三维结构及其重联图像. 结果发现, IMF B_y为正时, 在北极隙区附近尾-昏侧存在IMF与地磁场之间稳定持续的重联现象;参与重联的地球磁场既有闭合磁力线也有开放磁力线;IMF在北极隙区与地球闭合磁力重联后一端与南磁极相连的磁力线在尾向运动时还可能与北尾瓣的开放磁力线重联而重新闭合, 这种重联与磁力线循环过程不同于同一条IMF磁力线分别在南北半球与地磁场重联的模型. 南极隙区的重联发生在尾-晨侧, 其动力学过程与北极隙区情形类似. 我们的模拟结果表明, IMF B_y较大时不可能发生IMF同一条磁力线分别在南北极隙区重联的情形, 也不会因此而减少尾瓣的开放磁力线.     

A new mechanism for the magnetic enhancement of hematite during heating: the role of clay minerals

The magnetic properties of loess, lake, and ocean sediments are often used as indicators for paleoclimatic/paleoenvironmental changes. Thermomagnetic analysis is a conventional approach for identifying magnetic phases and thermal alteration of samples. Magnetic concentration parameters are often enhanced after thermal treatment. In this study, the role of clay minerals in magnetic enhancement at elevated temperatures is systematically investigated. The results indicate that the clay minerals (saponite, Ca-montmorillonite, kaolinite, and chlorite) are dominated by paramagnetic behaviour and that the magnetic properties remain relatively stable after heating to 700°C in argon. In contrast, mixtures of hematite and chlorite have a high degree of magnetic enhancement after heating in argon, which indicates that clay minerals play important role in magnetic enhancement. These results improve our understanding of the processes involved in complicated mineral transformations, which is important for retrieving paleoclimatic/paleoenvironemntal signals from magnetic proxies.     

Interchange instability as a mechanism of magnetotail current disruption at the magnetic storm recovery phase

The theory of relaxation of geomagnetic depression observed during magnetic storm has been proposed based on the knowledge of the interaction between the Dst index and the magnetotail current. It has been indicated that the disruption of the tail current that was enhanced during the storm main phase can be caused by the interchange instability, which develops in the boundary plasma sheet due to the sheet curvature in the near to the Earth region and due to a sharp, directed toward the curvature center, plasma pressure gradient at the boundary between the plasma sheet and the tail lobe. The dispersion equation and expression for the instability growth rate have been obtained. The theoretically predicted characteristic time of storm depression relaxation τ is ～10 h and is in good agreement with the experimental estimate.     

Magnetic properties of Antarctic shergottite meteorites EETA 79001 and ALHA 77005: possible relevance to a Martian magnetic field

The possibility that the parent body of the SNC meteorites is Mars implies that the magnetic properties of these meteorites may provide evidence concerning ancient Martian magnetic fields. EETA 79001 possesses a weak, very stable primary magnetization, the properties of which are consistent with its acquisition in an ambient magnetic field either during the meteorite's formation or during the severe shock event later in its history. The samples of ALHA 77005 studied possessed no measurable primary magnetization: the observed remanence appears to be a viscous magnetization acquired in local laboratory fields. The magnetic carriers in the meteorites are fine-grained magnetite and a lower Curie point mineral, probably titanomagnetite or pyrrhotite, present to the extent of less than 0.1% by weight. Estimates of the strength of the magnetizing field for EETA 79001 are in the range 1–10 μT.     

数值模拟日侧磁场重联对极盖等离子体云块形成的影响

极盖等离子体云块是极区空间天气重要现象之一,其形成过程是当前重要研究课题.观测表明,日侧磁场重联对应的极区电离层高速流可能对舌状等离子体(TOI)形成"切割"作用,最终形成极盖等离子体云块.伴随磁场重联,同时存在极光粒子沉降,会引起F层等离子体密度的增大,阻碍"切割"效应.本文利用耦合极区电离层模型,模拟研究电场和软电子沉降共同作用下F层等离子体密度的演化.结果表明,在局部电离层电场大于一定数值(80 mV)的情况下,"切割"效应能有效发生.并详细分析了"切割"效应发生时等离子体各参量的演化过程,对"切割"效应的内在物理过程进行了探讨.     

The structure and origin of magnetic clouds in the solar wind

Plasma and magnetic field data from the Helios 1/2 spacecraft have been used to investigate the structure of magnetic clouds (MCs) in the inner heliosphere. 46 MCs were identified in the Helios data for the period 1974–1981 between 0.3 and 1 AU. 85% of the MCs were associated with fast-forward interplanetary shock waves, supporting the close association between MCs and SMEs (solar mass ejections). Seven MCs were identified as direct consequences of Helios-directed SMEs, and the passage of MCs agreed with that of interplanetary plasma clouds (IPCs) identified as white-light brightness enhancements in the Helios photometer data. The total (plasma and magnetic field) pressure in MCs was higher and the plasma- lower than in the surrounding solar wind. Minimum variance analysis (MVA) showed that MCs can best be described as large-scale quasi-cylindrical magnetic flux tubes. The axes of the flux tubes usually had a small inclination to the ecliptic plane, with their azimuthal direction close to the east-west direction. The large-scale flux tube model for MCs was validated by the analysis of multi-spacecraft observations. MCs were observed over a range of up to 60° in solar longitude in the ecliptic having the same magnetic configuration. The Helios observations further showed that over-expansion is a common feature of MCs. From a combined study of Helios, Voyager and IMP data we found that the radial diameter of MCs increases between 0.3 and 4.2 AU proportional to the distance, R, from the Sun as R^0.8 (R in AU). The density decrease inside MCs was found to be proportional to R^–2.4, thus being stronger compared to the average solar wind. Four different magnetic configurations, as expected from the flux-tube concept, for MCs have been observed in situ by the Helios probes. MCs with left-and right-handed magnetic helicity occurred with about equal frequencies during 1974–1981, but surprisingly, the majority (74%) of the MCs had a south to north (SN) rotation of the magnetic field vector relative to the ecliptic. In contrast, an investigation of solar wind data obtained near Earths orbit during 1984–1991 showed a preference for NS-clouds. A direct correlation was found between MCs and large quiescent filament disappearances (disparition brusques, DBs). The magnetic configurations of the filaments, as inferred from the orientation of the prominence axis, the polarity of the overlying field lines and the hemispheric helicity pattern observed for filaments, agreed well with the in situ observed magnetic structure of the associated MCs. The results support the model of MCs as large-scale expanding quasi-cylindrical magnetic flux tubes in the solar wind, most likely caused by SMEs associated with eruptions of large quiescent filaments. We suggest that the hemispheric dependence of the magnetic helicity structure observed for solar filaments can explain the preferred orientation of MCs in interplanetary space as well as their solar cycle behavior. However, the white-light features of SMEs and the measured volumes of their interplanetary counterparts suggest that MCs may not simply be just H-prominences, but that SMEs likely convect large-scale coronal loops overlying the prominence axis out of the solar atmosphere.     

Dynamics of the radiation belt formed by solar protons during magnetic storms

Experimental proofs of the existence of the formation and destruction mechanisms of solar proton belts in the inner magnetosphere at a rapid change in the penetration boundary of solar protons are presented. An analysis of the measurements of solar protons and alpha-particles on board the Coronas-F low-altitude polar satellite during the magnetic storms in October–November 2003 is performed. During this period, formation and destruction of the belts of solar cosmic rays was observed several times. The compression of the magnetosphere during a storm makes possible the direct penetration of solar protons deep into the inner magnetosphere. The proton trajectories outside the penetration boundary are open, and the preliminary captured particles can easily leave the magnetosphere. During the recovery of the magnetospheric configuration, when the penetration boundary goes away from the Earth, the solar protons and alpha-particles with relatively low velocity of the magnetic drift remain stably captured, whereas the particles of higher energies follow the motion of the penetration boundary. That is why the energy range of the captured protons is limited from above in contrast to the effect of injection during ineffective SC in the low-energy region.     

雄安牛驼镇凸起区高渗性白云岩对上覆地层温度场的影响

牛驼镇凸起区内岩溶型白云岩广泛发育,其层内地下水对流造成浅表温度异常,沉积盖层段的地温梯度值为50.0℃·km-1,但随着高渗性白云岩埋深的增加,上覆沉积盖层段地温梯度值逐渐减小.本文以6口钻井测温曲线和213块样品热物性资料为基础,对高渗性白云岩层内流体对流对上覆地层温度影响的大小开展水热耦合研究.结果表明：一定厚度高渗透层随着其埋深的增加对浅部地层温度的影响减小,2.0 km厚度高渗层其温度影响范围在3.0 km左右;当高渗透层埋深一定时,其温度影响会随着其厚度的增加而增大.其次,通过安01测温曲线获取牛驼镇凸起底部变质基岩温度场特征,地温梯度值为18.6℃·km-1,结合其热导率值,计算知热流值在58.2 mW·m-2左右.通过该热流值累加上上部碳酸盐和沉积岩层生热率热流值贡献,得知牛驼镇凸起区及周边真实地表热流值为59.6 mW·m-2左右.相比于受到地下水对流或热折射效应影响的沉积盖层段90.0 mW·m-2的"热流值",通过该变质基岩层段计算出的地表热流值更加能够反映该区域的热流值背景.     

The “fan” instability as a possible generating mechanism of vlf quarter-gyrofrequency emissions during the recovery phase of a magnetospheric storm

Summary VLF quarter-gyrofrequency emissions, whose experimental characteristics differ from those of discrete plasmaspheric emissions usual during active times, have been observed by low-altitude Intercosmos 24 and Magion 2 satellites within the plasmasphere during periods of quieting geomagnetic activity. A new kind of instability is proposed which could lead to the production of these emissions. It is shown that quasi-electrostatic whistler waves can be generated in the eqquatorial region due to the fan instability, with maximum growth rate and spectral energy density in a frequency band below one half of the equatorial electron gyrofrequency. The observations of low-energy electrons and plasma waves in the equatorial region within or in the vicinity of the plasmapause, which could support our hypothesis experimentally, are discussed.     

木星磁尾重联产生的磁通量管向内运动的数值模拟

本文通过利用包含离心力的自洽、轴对称稳态木星磁层模型,以及等离子体细丝运动理论对磁尾重联产生的磁通量管向内输运进行研究.基于细丝运动理论模型,通过MHD数值模拟我们可以得到磁通量管随时间变化的许多特性.模拟结果表明,重联产生的磁通量管向内运动可到达10R_J以内,磁通量管赤道部分的速度可以达到350 km·s^-1左右,表现出很强的向行星方向的流动.初始磁通量管中的等离子体密度和压强均小于周围介质,随着它迅速向木星方向运动,它的等离子体密度由于体积压缩逐渐上升,等离子体压强则逐渐上升到与周围介质相当.磁通量管在电离层上足点向赤道方向的运动滞后于它在赤道面上向行星方向的运动.

     

Magnetic properties of the Olivenza meteorite—possible implications for its evolution and an early solar system magnetic field

The magnetic properties of samples of the Olivenza chondrite (LL5) obtained from four collections have been investigated. The natural remanent magnetization (NRM) consists of a very stable primary component, which is randomly scattered in direction on a scale of 1 mm³ or less within the samples, and a secondary magnetization widely varying in intensity, and probably also in direction. The origin of the secondary NRM is not clear, and may be of terrestrial origin. It is concluded that the NRM is carried by the ordered nickel-iron mineral, tetrataenite. The origin of the primary NRM could be a magnetic field associated with the solar nebula, out of which the metal grains condensed and acquired a thermo-remanent magnetization (TRM), or Olivenza could be a fine-grained breccia, the constituent fragments possessing randomly directed magnetization. The implications for the origin and evolution of Olivenza and its parent body if the former magnetizing process has occurred are discussed.     

MT-index - a possible new index to characterize the magnetic configuration of magnetotail

Existing activity indices (magnetic indices like AE, K_p, D_st or indices based on solar wind parameters) are poor predictors of the instantaneous magnetospheric configuration. We suggest a new activity index - the MT-index. It is defined as the invariant latitude of the isotropic boundary (IB) of \uparrow100 keV protons reduced to the midnight meridian. This IB is a low-altitude signature of the boundary between regions of adiabatic and chaotic regimes of particle motion in the tail current sheet which is controlled by the magnetic field in the equatorial near-Earth tail (at 5-10R_e). We have investigated the local time and activity dependence of the IB latitude based on data from about 2000 orbits of NOAA spacecraft. By finding the formula to reduce the IB latitude to midnight meridian, we then evaluate the accuracy of the derived index. We compared the MT-index with the magnetic field measured simultaneously by geosynchronous GOES-2 spacecraft and showed that, unlike the traditional indices, the MT-index displays a good correlation (r\uparrow0.9) with the magnetic field inclination in the nightside portion of the geosynchronous orbit. It is, thus, a good measure to characterize quantitatively the tailward stretching of the tail magnetic field. Based on the measured MT value, a simple numerical procedure is suggested to choose the version of the T89 magnetospheric model. We conclude that the MT-index is the best known predictor of the instantaneous magnetic configuration in the near-Earth magnetotail. It may be available on a regular basis and can be implemented for scientific studies.     

Deformation of the magnetosphere and the penetration boundary of solar protons before the onset of the main phase of a magnetic storm

The ring current is conventionally considered responsible for the shift of the boundary of solar proton penetration into the inner Earth’s magnetosphere during magnetic storms. The cases of a boundary shift were observed in some works on the dark side before the onset of a magnetic storm, i.e., at positive values of the Dst index. In this work, this type of shift of the penetration boundary is considered in detail with two storms as examples. It is shown that the corresponding distortion of the magnetosphere configuration is induced by an increase in the solar wind pressure during the initial phase of a magnetic storm. The current induced in this case on the magnetopause is closed by a current in the equator plane, which changes the configuration of the dark side of the inner magnetosphere, weakens the magnetic field, and allows solar protons to penetrate the inner magnetosphere. The significant difference in the positions of the penetration boundary and the boundary found from models of the magnetosphere magnetic field can be explained by insufficient consideration of closing currents.     

水介质对水下目标体磁场的影响

根据扬子江航道上一系列磁测及验证结果,指出在不同介质中的相似磁性物体所引起的磁场强度会产生一定的变化,实例说明：这一现象可能对磁法勘查带来的影响.文章没有对不同介质中磁性体磁场的变化机制进行讨论.     

A fluid-filled fracture as possible mechanism of ground deformation at Phlegraean Fields,Italy

Two uplift episodes have recently been recorded at Phlegraean Fields, a volcanic region near Naples (south-central Italy). The first episode occurred in 1970 and lasted up to 1972; the second has begun at the end of 1982 and is still in progress.An attempt to model the ground deformations which occurred during the 1970–1972 event is made in this paper. The source has been assumed to be a two-dimensional fluid-filled fracture, similar to a sill. A good fit with experimental data has been obtained for a short (1–2 km long) shallow (3 km deep) source and a driving pressure ranging from 60 to 210 bars. Rigidity values have been fixed at 3.5–4.0 × 10¹⁰ c.g.s., with Poisson ratio equal to 0.3.This solution which differs from previous approaches byMogi (1958) andWalsh andDecker (1971) is non-unique, but the present results are in good agreement with observed horizontal and vertical displacements. Notwithstanding the oversimplification made in assuming a homogeneous elastic semi-infinite medium, the predicted stress field seems to be in agreement with the fault-plane solutions and the pattern of epicenters determined for the uplift-seismic swarm episode that is still in progress.