Contribution of the ground corona ions to the convective charging mechanism

The convective charging mechanism of thunderclouds is based on the vertical transport of space charge generated by corona from ground irregularities under the influence of the surface electric field. The present work estimates the amount of charge which is expected to reach cloud base by conduction and convection processes during the lifetime of a thunderstorm. This estimate is made using the numerical model PICASSO, previously designed to characterize the evolution of this corona space charge between ground level and cloud base. Experimentally determined values of surface electric field are introduced into the model in order to initiate the computation. These values are based on six events documented during four different field experiments carried out in Florida and in France. As an upper limit, the convective transport is uniformly applied as a linearly increasing vertical air speed profile and competes with the conductive transport. The fraction of the positive charge generated at the surface by corona which finally reaches the upper limit of the layer varies between 26 and 86%, essentially depending on the electric field evolution at altitude. Assuming that the vertical transport conditions remain the same over an area of 10 km×10 km, the overall charge amount can be roughly estimated. It ranges between about 63 and over 300 C. Because the present assumptions probably lead to an overestimate of these amounts, such a range suggests that the convective charging mechanism is unlikely to be able to account for the major electrification process of the thundercloud. However, it could be considered as a relevant mechanism contributing to the lower positive charge center of the thundercloud, often observed close to cloud base.     

引力场中磁场重联的数值研究(IV)多层电流片

应用数值方法研究了日冕多层电流片中电阻撕裂模不稳定性的非线性演化和磁场重联过程,结果表明,计算区域顶部附近两侧电流片中的磁岛和等离子体团向上抛射,并携出大量的磁能和热能;中心电流片中的磁岛向下运动,逐渐演变成底部含有３个磁闭合区的冕流结构。进而在中心电流片中再次发生磁场重联,多次形成向下运动的小型磁岛,并与底部磁闭合区发生结合不稳定性。同时在磁闭合区中也有磁场重联发生,导致中心小磁闭合区的湮灭。初始电流片之间的距离趋近,上述演化过程越快。日冕多层电流片中的磁场重联过程可能对日冕物质抛射和日冕加热有着重要影响。     

日冕物质抛射和射电爆发

日冕物质抛射（ＣＭＥ） 是一个极为复杂的动力学过程本文基于开放场、闭合场的物理条件及射电爆发理论, 研究了ＣＭＥｓ 与相伴随的射电Ⅱ型、Ⅲ型、Ⅳ型爆发、软χ射线增强及太阳耀斑的关系给出了它们相伴随的条件： 当磁通量喷发, 能量释放时, 等离子体将被加速如果加速区在开放场, 可能会产生Ⅲ型爆发; 如果是闭合场, 被加速的高能质子和高能电子将被磁环捕获高能质子在磁环腿部呈损失锥分布, 当Ｅ≥ＥＴ 时会产生软χ射线增强随着磁环内的热压Ｐ和磁压Ｐｍ 的升高, 当β≥βＴ 时, 磁环将炸裂, 产生ＣＭＥｓ抛射出的高能相对论电子绕开放场线作螺旋飞行时, 会产生Ⅳ型爆发; 而亚相对论电子以零入射角沿开放磁场线逃逸时, 会产生Ⅲ型爆发高速飞行的等离子体产生激波时, 会产生Ⅱ型爆发当ＣＭＥｓ 源接近耀斑时, 会触发耀斑爆发     

Monte Carlo Simulation of Solar Active-Region Energy

A Monte Carlo approach to solving a stochastic-jump transition model for active-region energy (Wheatland and Glukhov: Astrophys. J. 494, 858, 1998; Wheatland: Astrophys. J. 679, 1621, 2008) is described. The new method numerically solves the stochastic differential equation describing the model, rather than the equivalent master equation. This has the advantages of allowing more efficient numerical solution, the modeling of time-dependent situations, and investigation of details of event statistics. The Monte Carlo approach is illustrated by application to a Gaussian test case and to the class of flare-like models presented in Wheatland (Astrophys. J. 679, 1621, 2008), which are steady-state models with constant rates of energy supply, and power-law distributed jump transition rates. These models have two free parameters: an index (δ), which defines the dependence of the jump transition rates on active-region energy, and a nondimensional ratio ( ) of total flaring rate to rate of energy supply. For the nondimensional mean energy of the active-region satisfies , resulting in a power-law distribution of flare events over many decades of energy. The Monte Carlo method is used to explore the behavior of the waiting-time distributions for the flare-like models. The models with δ≠0 are found to have waiting times that depart significantly from simple Poisson behavior when . The original model from Wheatland and Glukhov (Astrophys. J. 494, 858, 1998), with δ=0 (i.e., no dependence of transition rates on active-region energy), is identified as being most consistent with observed flare statistics.     

山东昌乐新近纪玄武岩中刚玉巨晶反应边的成因

通过对山东昌乐方山新近纪碱性玄武岩中原生刚玉巨晶的观察研究,发现在刚玉巨晶与玄武岩间存在反应边,可见新近纪碱性玄武岩中的刚玉巨晶为捕虏晶。电子探针下观察,反应边有两类:第1类由尖晶石带和钛磁铁矿 熔体带构成,第2类由尖晶石带和长石 钛磁铁矿带构成。在第1类反应边中,尖晶石带很窄(<40μm),钛磁铁矿 熔体带较宽(100～120μm);而且尖晶石的成分变化很大,从靠近刚玉一侧(内侧)向外,Al_2O_3逐渐降低,从85.08%～58.94%,MgO和FeO逐渐升高,分别从5.14%～14.82%和8.08%～28.24%。在第2类反应边中,尖晶石带较宽且稳定(100μm左右);长石 钛磁铁矿带不稳定,特别是钛磁铁矿不但窄(<40μm),而且分布断断续续;尖晶石的成分变化较小,Al_2O_359.25%～62.82%、MgO 12.34%～13.50%、FeO 23.25%～27.37%。本文对两类反应边的形成模式进行了探讨,认为刚玉巨晶与玄武岩浆反应持续时间的长短是导致形成两类反应边的主要因素,第1类反应边是反应没有达到平衡的产物,第2类反应边为反应平衡或者是接近平衡的产物。     

高能离子束流引起低频电磁波动的特性

理论和数值模拟研究了日冕区高速低密离子束流与等离子体相互作用产生的低频电磁波动特征. 结果表明,在线性阶段,系统波动主要表现为短波长的非共振模的激发;在非线性阶段,长波模占优,短波长波逐渐衰减,此时系统波动表现为具有Alfvén波动特征,波的能谱为双幂律谱. 这些结果可用来解释太阳风中的Alfvén湍动现象.     

射电运动Ⅳ型爆发和日冕物质抛射

射电Ⅳ型运动爆发同日冕物质抛射（ＣＭＥｓ）关系极为密切。本文基于对Ⅳ型运动爆发的研究以及ＣＭＥｓ开放场的物理条件,探讨了ＣＭＥｓ形成及抛射的物理条件。由于磁通量突然喷发,能量大量释放,在ＣＭＥ闭合场中的等离子体被加速,导致高能质子和高能电子被大磁环捕获。随着磁环内的热压Ｐ和磁压Ｐｍ的升高,当β＞βＴ时磁环将炸裂,从而产生ＣＭＥｓ。抛射出的未离化的等离子体团将产生等离子体基波与谐波辐射。随着等离子体的不断离化,高能相对论电子绕开放磁场线作螺旋飞行,这时等离体辐射降到次要地位,回旋同步加速辐射上升到主导地位,这就是射电Ⅳ型运动爆发。如果离化的早,则在微波波段也能看到Ⅳ型运动爆发。这就是微波Ⅳ型爆发,也是微波Ⅳ型爆发罕见的原因。射电运动Ⅳ型爆发源就是日冕抛射的物质。     

The Recovery of CME-Related Dimmings and the ICME’s Enduring Magnetic Connection to the Sun

It is generally accepted that transient coronal holes (TCHs, dimmings) correspond to the magnetic footpoints of CMEs that remain rooted in the Sun as the CME expands out into the interplanetary space. However, the observation that the average intensity of the 12 May 1997 dimmings recover to their pre-eruption intensity in SOHO/EIT data within 48 hours, whilst suprathermal unidirectional electron heat fluxes are observed at 1 AU in the related ICME more than 70 hours after the eruption, leads us to question why and how the dimmings disappear whilst the magnetic connectivity is maintained. We also examine two other CME-related dimming events: 13 May 2005 and 6 July 2006. We study the morphology of the dimmings and how they recover. We find that, far from exhibiting a uniform intensity, dimmings observed in SOHO/EIT data have a deep central core and a more shallow extended dimming area. The dimmings recover not only by shrinking of their outer boundaries but also by internal brightenings. We quantitatively demonstrate that the model developed by Fisk and Schwadron (Astrophys. J. 560, 425, 2001) of interchange reconnections between “open” magnetic field and small coronal loops is a strong candidate for the mechanism facilitating the recovery of the dimmings. This process disperses the concentration of  “open” magnetic field (forming the dimming) out into the surrounding quiet Sun, thus recovering the intensity of the dimmings whilst still maintaining the magnetic connectivity to the Sun. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Microwave Neutral Line Associated Source and a Current Sheet

Neutral Line associated Sources (NLSs) are quasi-stationary microwave sources projected onto vicinities of the neutral line of the photospheric magnetic field. NLSs are often precursors of powerful flares, but their nature is unclear. We endeavor to reveal the structure of an NLS and to analyze a physical connection between such a source with a site of energy release in the corona above NOAA 10488 (October/November 2003). Evolution of this AR includes emergence and collision of two bipolar magnetic structures, rise of the main magnetic separator, and the appearance of an NLS underneath. The NLS appears at a contact site of colliding sunspots, whose relative motion goes on, resulting in a large shear along a tangent. Then the nascent NLS becomes the main source of microwave fluctuations in the AR. The NLS emission at 17 GHz is dominated by either footpoints or the top of a loop-like structure, an NLS loop, which connects two colliding sunspots. During a considerable amount of time, the emission dominates over that footpoint of the NLS loop, where the magnetic field is stronger. At that time, the NLS resembles a usual sunspot–associated radio source, whose brightness center is displaced towards the periphery of a sunspot. Microwave emission of an X2.7 flare is mainly concentrated in an ascending flare loop, initially coinciding with the NLS loop. The top of this loop is located at the base of a non-uniform bar-like structure visible in soft X-rays and at 34 GHz at the flare onset. We reveal i) upward lengthening of this bar before the flare onset, ii) the motion of the top of an apparently ascending flare loop along the axis of this bar, and iii) a non-thermal microwave source, whose descent along the bar was associated with the launching of a coronal ejection. We connect the bar with a probable position of a nearly vertical diffusion region, a site of maximal energy release inside an extended pre-flare current sheet. The top of the NLS loop is located at the bottom of this region. A combination of the NLS loop and diffusion region constitutes the skeleton of a quasi-stationary microwave NLS.