Effects of the interplanetary magnetic field clock angle on the shape of bow shock

Using the global magnetohydrodynamics(MHD) simulation model, we investigated the effects of the interplanetary magnetic field(IMF) clock angle on the shape of bow shock, including its rotational asymmetry and subsolar point. For general northward IMF( z component Bz 0), the rotational symmetry of the bow shock is broken by the effects of fast magnetosonic Mach number(Mms), and the cross-sectional line of the bow shock is an ellipse with the semi-major axis along the direction perpendicular to the IMF. The ratio or D-value between semi-major and semi-minor axis can be used to illustrate the extent of asymmetry of the bow shock. On the basis of the multiple parameters fitting, we obtain the changing relationship of both semi-axes with the clock angle and the distance away from the Earth. For general southward IMF(Bz 0), the cross sectional line of the bow shock is highly asymmetrical under the multiple effects of magnetopause and Mms. The effects of IMF clock angle on subsolar point depend mainly on the changing subsolar point of magnetopause as an obstacle. The distance of subsolar point of bow shock from the Earth increases with the increasing IMF clock angle for Bz 0, and decreases with the increasing IMF clock angle for Bz 0.     

地球弓激波的旋转非对称性

通过对太阳风-磁层-电离层系统的全球MHD模拟,研究地球弓激波相对日地连线的旋转非对称性．模拟限于太阳风速度沿日地连线、地球磁偶极矩和行星际磁场（IMF）与日地连线垂直的简单情况．模拟结果表明,即便对于IMF强度为零的情况,弓激波相对日地连线也不具备旋转对称性质：终端面（晨昏子午面）及其向阳侧的弓激波截线的东西宽度大于南北宽度（约9%~11％）,终端面尾侧的弓激波截线东西宽度小于南北宽度（约8％）．在存在IMF的情况下,弓激波的位形同时受到磁层顶的形状和快磁声波速度各向异性的影响．磁层顶向外扩张并沿IMF方向拉伸,且其扩张和拉伸程度随IMF由北转南而增强．在磁鞘中,垂直于磁场方向的快磁声波速度高于平行方向．因此,磁层顶拉伸方向与快磁声波速度最大方向垂直,它们对弓激波位置的效应恰好相反;弓激波的最终形状取决于何种效应占据主导地位．对于终端面尾侧,快磁声波速度的各向异性起主导作用,弓激波截线沿IMF垂直方向的宽度大于平行方向．对于终端面及其向阳侧,弓激波截线的形状与IMF取向有关：在准北向或晨昏向IMF情况下,弓激波截线沿IMF垂直方向的宽度仍大于平行方向;在准南向IMF情况下,弓激波截线沿IMF垂直方向的宽度小于平行方向的．鉴于弓激波形状同IMF取向之间的密切关系,我们提议以IMF为基准方向,提取弓激波截线的平行半宽度R_b∥和垂直半宽度R_b⊥作为尺度参数．这些尺度参数和通常引入的弓激波截线的东西半宽度y_b和南北半宽度z_b相比,更为合理地表征了弓激波的几何性质．模拟结果表明,在终端面上,y_b/z_b和R_b∥/R_b⊥在IMF各向同性取向下的统计平均值均低于1,与观测得到的结论一致.     

扩展的倾斜角和倾斜角总水平导数方法

为了突出显示重磁场中地质体分布、断裂构造特征等信息,使图像显示错落有序、层次分明、清楚直观,有利于解释人员从不同角度认识重磁场异常特征.本文通过分析倾斜角概念,根据反余切函数特性,提出了扩展的倾斜角(iTdr)和倾斜角总水平导数(iTdr_Thdr)方法,来增强重磁异常信息,突出异常形状特点,以便于识别重磁异常中地质体边界和提取地质体分布、断裂构造平面展布特征等信息.理论模型和实际资料对比分析表明该方法简单、实用、具有较好的识别效果和较高的分辨能力,能够获取丰富的地质信息,对识别地质体边界、划分大地构造单元、确定断裂带和地质构造走向等具有实际意义.     

地球弓激波及其与行星际激波相互作用

给定地球轨道附近的行星际条件和地球弓激波的几何位形,本文分析向阳侧弓激波强度参数沿激波阵面的分布,以及行星际激波与弓激波的相互作用.对于弓激波阵面相对日地连线轴对称的情形,得到如下结论：（1）弓激波强度参数分布相对由行星际磁场和日地连线构成的基准面对称,各激波强度参数的最大值出现在基准面上.磁压比在垂直激波线一侧较大,而气压比在平行激波点一侧较大,导致总压比相对日地连线大致呈轴对称分布.（2）随着行星际磁场与日地连线夹角的增大,弓激波强度参数的最大值有所减小,且位置朝远离日下点方向偏移;但气压比和总压比的分布基本上不受影响.（3）行星际激波透过弓激波之后,切向磁场比更接近于1,但总磁场跳变幅度增大.（4）透过弓激波之后,行星际准垂直激波的总磁场比更接近于1,准平行激波的总磁场比则反之.     

Asymmetry of nonlinear interactions of solar MHD discontinuities with the bow shock

Oblique interaction between the solar fast shock wave, which is a typical nonstationary strong discontinuity in the interplanetary space, and the bow shock front upstream of an Earth-type planetary magnetosphere is studied. Attention has been paid to the qualitative and quantitative (with respect to the proton density distribution) dawn-dusk (or morning-evening) asymmetry of the discontinuities refracted into the magnetosheath, which originates in the ecliptic plane on different sides of the Sun-Earth line. The results under discussion have been corroborated experimentally by the gas-kinetic pattern of the bow-shock front and the WIND and ISEE 3 spacecraft measurements of the plasma density.     

Interpretation of tensor gravity data using an adaptive tilt angle method

Full Tensor Gravity Gradiometry (FTG) data are routinely used in exploration programmes to evaluate and explore geological complexities hosting hydrocarbon and mineral resources. FTG data are typically used to map a host structure and locate target responses of interest using a myriad of imaging techniques. Identified anomalies of interest are then examined using 2D and 3D forward and inverse modelling methods for depth estimation. However, such methods tend to be time consuming and reliant on an independent constraint for clarification. This paper presents a semi‐automatic method to interpret FTG data using an adaptive tilt angle approach. The present method uses only the three vertical tensor components of the FTG data (T_zx, T_zy and T_zz) with a scale value that is related to the nature of the source (point anomaly or linear anomaly). With this adaptation, it is possible to estimate the location and depth of simple buried gravity sources such as point masses, line masses and vertical and horizontal thin sheets, provided that these sources exist in isolation and that the FTG data have been sufficiently filtered to minimize the influence of noise. Computation times are fast, producing plausible results of single solution depth estimates t hat relate directly to anomalies. For thick sheets, the method can resolve the thickness of these layers assuming the depth to the top is known from drilling or other independent geophysical data. We demonstrate the practical utility of the method using examples of FTG data acquired over the Vinton Salt Dome, Louisiana, USA and basalt flows in the Faeroe‐Shetland Basin, UK. A major benefit of the method is the ability to quickly construct depth maps. Such results are used to produce best estimate initial depth to source maps that can act as initial models for any detailed quantitative modelling exercises using 2D/3D forward/inverse modelling techniques.     

Characteristics of the double layer associated with terrestrial bow shock by THEMIS observation

This study presents observation and detailed analysis on the double layers(DLs) in the ramp and the foreshock contacting with the foot of the terrestrial bow shock by THEMIS on September 14, 2008 under enhanced dynamic pressure in the solar wind. The results reveal that:(1) The time duration of the double layers is mainly 3–8 ms, and their max parallel electric field is minus 10–40 m V/m.(2) On assuming a propagation speed at the ion acoustic speed(?s), their spatial scale is estimated to be 0.3–1.15 km(about 75–200 ?D).(3) The net potential drop of DLs is estimated to be 5–32 V.(4) The DLs in the ramp and the foreshock contacting to the foot of the bow shock is current-carrying as a result of development and evolution of nonlinear phase of instability in the self-consistent current-carrying plasma. The DLs may play an important role in strong turbulence in the foreshock contacting with the foot of the bow shock.     

电离层电导对地球磁层顶和舷激波尺度的影响

本文在如下假定下分析电离层电导对地球磁层顶和舷激波尺度的影响：（1）对电离层采用球壳近似,Pedersen电导ΣP均匀,Hall电导为零;（2）地磁偶极矩处于正南方向,行星际磁场（IMF）只有南向分量（BzBz和ΣP,通过三维全球MHD模拟获得系统的准定态.结果表明,在大约1～5 S范围内,ΣP值显著影响磁层顶和舷激波的尺度,而在该范围之外则几乎没有影响.随着ΣP的增加,磁层顶和舷激波整体向外扩张,前者的扩张程度低于后者,以至磁鞘区的范围扩大.磁层顶的侧翼点的位置随ΣP的变化与Bz的幅度有关：在弱南向IMF情况下磁层顶的侧翼点随ΣP的增加向内移动,而在强南向IMF情况下则向外移动.上述结果表明,在构建磁层顶和舷激波的经验模型时,有必要计入电离层电导的影响.     

应用加强解析信号倾斜角进行位场数据的边界检测

边界检测在地球物理位场数据解释中占有重要位置.现有的传统边界识别方法有的不能同时显示不同振幅的异常边界,有的虽然能均衡不同振幅的异常,但识别出来的边界信息中含有一些额外的错误的边界信息,尤其是当测量的异常中同时含有正异常和负异常时.目前已有的去除额外错误边界信息的方法存在着一定的人为主观性.为了解决这些问题,本文定义了加强解析信号倾斜角来进行地质体边界识别.通过模型试验证明了该方法不仅能同时清晰地识别深部和浅部地质体的边界,而且能有效地避免引入一些错误边界信息.最后将该方法应用到四川盆地的重力异常数据中,并取得了良好边界结果.     

行星际磁场B_y对弓激波影响的MHD结果

利用全球磁流体模拟的结果,本文研究了行星际磁场B_y对弓激波位型的影响.结果显示:随着行星际磁场B_y绝对值的增大,弓激波的日下点距离、旋转对称张角、南北非对称性以及旋转非对称性均随之增加.其中,B_y对弓激波日下点距离的影响可达5 RE左右.东向B_y和西向B_y对弓激波位型影响具有对称性,东向B_y和西向B_y大小相同时弓激波日下点距离、旋转对称张角以及旋转非对称性参数均相同,而南北非对称性参数大小相同正负相反.行星际磁场B_y占主导时弓激波尾部横截面在南北方向上拉伸,并且拉伸程度随着B_y绝对值的增大而增大,弓激波尾部横截面的拉伸现象与磁声波马赫数密切相关.     

火星弓激波上游高能拾起氧离子实例分析

火星外逸层中的氧原子(O)经光致电离、电荷交换或电子碰撞产生氧离子(O+), 新生O+随即被太阳风拾起, 进而被对流电场加速.这些O+被称为"拾起"O+.2018年11月17日08∶54∶00—10∶24∶00 UT期间, 火星大气和挥发物演化任务(Mars Atmosphere and Volatile EvolutioN, MAVEN)卫星从上游太阳风进入磁鞘中, 持续观测到背离太阳运动的高能拾起O+(约30 keV), 在相空间呈现为初速度不为零的部分环分布.分析表明: 这部分高能O+的初始能量较高, 回旋半径较大, 位于摆线运动的高能区域, 穿越火星弓激波进入磁鞘, 离子在该范围内能量变化不显著, 只是使得相应环分布在穿越弓激波后发生偏转.这些结果有助于进一步认识火星空间高能拾起O+的产生与运动轨迹.     

用AB连线与主震位置的关系判断未来主震的震中范围

地震活动图像的Ａ（最大前震）、Ｂ（第二大前震）两点的连线与主震位置有明显的关系，用此判断未来主震的震中范围，其效果颇好，再加其它资料的配合，使判断精度提高。此方法的资料自检符合率，陆地达９２％。震例检验的效果也较好。     

利用倾斜角总水平导数和欧拉反褶积法研究四川盆地线性构造

汶川地震的发生引发了新一轮对龙门山及邻区断裂特征研究的热潮.倾斜角总水平导数是近几年常用的一种高分辨率边界识别方法,欧拉反褶积法是一种自动估算场源体位置和深度的方法,本文联合以上两种方法对区域重、磁资料进行处理,根据处理结果在研究区内划分出14条断裂,并对断裂的位置、走向、深度等特征进行了详细的描述.本文的成果为研究区...     

Sympathetic flaring with BATSE,GOES, and EIT data

Sympathetic flaring is defined as the initiation of a solar flare as a result of a transient phenomenon occurring elsewhere on the Sun. Discovery of sympathetic flaring or lack thereof, may lead to a greater understanding of the physics of flare initiation. Knowledge of a mechanism for initiating solar flares would also aid in predicting at least some solar flares. Two studies of sympathetic flaring are presented in this paper. The first part of the paper presents a test for sympathetic flaring in flares observed with the Burst and Transient Source Experiment. A Monte Carlo simulation is used to compare the distribution of solar X-ray flares in time to that expected from a time-varying, Poisson distribution. No evidence for sympathetic flaring is found, though it cannot be ruled out. The X-ray flare data also do not allow discovery of sympathetic flares occurring within 2 min of the initial flare. Because the observations do allow for at least some flares to occur sympathetically, the second part of the paper examines one possible mechanism for initiating flares. The mechanism examined is large-scale coronal transients observed by the SOHO/Extreme Ultraviolet Imaging Telescope: EIT waves. A comparison of the rate of flaring in the interval prior to an EIT wave to the rate of flaring while the wave traverses the solar disk shows no increase in the number of flares due to the EIT wave.     

平原新生代沉积层对天津地方震定位影响及改善途径的研究

天津台网地处燕山隆起与陆架海过渡带的华北平原，燕邻渤海湾，地形差异很大，台网为混合式，跨基岩山地和沉降平原，地壳上部结构复杂。直属子台蓟县台、宝坻台为地面记录，其余均为井下摆记录，各子台所在位置沉积覆盖层厚度差别较大，从0～4000m不等，速度结构差异极大。过去，天津台网定位采用北京地区均匀地壳速度模型，定位结果与全国地震月报目录相比，存在较大误差。     

Artificial spacecraft in hybrid simulations of the quasi-parallel Earth’s bow shock: analysis of time series versus spatial profiles and a separation strategy for Cluster

We construct artificial “software” spacecraft consisting of magnetometers and 3D thermal and energetic ion detectors. Four such spacecraft are “flown” through a 1D simulation of a quasi-parallel shock. We analyze the resulting time series from the spacecraft, and then use the more complete simulational information to evaluate our interpretations based on the limited times series information. The separation strategy used, with two closely spaced spacecraft pairs separated by a large distance, was helpful in the interpretation, since a variety of important processes operate over several different scale lengths. This work highlights the ability to draw inferences about spatially and temporally varying phenomena based on multiple-spacecraft time series data, and suggests that many spacecraft configurations which bear little resemblance to the classic Cluster tetrahedron may be necessary when multiple scale lengths are present.     

The Datong earthquake and its anomalous tilt Field

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地倾斜异常的一个特征及其应用

地倾斜与孕震地点存在一定的关系, 即强震前地倾斜的空间分布存在一定的有序性。 基于这一结果对张北地震前的地倾斜方向分布进行了研究, 显示张北地震前地倾斜方向确有指向或背向震中的趋势。 文中探讨了确定孕震区的方法, 利用截止到2004年8月的资料, 对华北、 新疆和川滇地区的地倾斜方向进行了研究。 在华北地区目前地倾斜方向线相交的区域有京津唐地区和山西带, 覆盖面积较大且较为分散, 难以勾画出显著的异常区。 在新疆和川滇地区也未发现类似张北地震前地倾斜方向线集中到同一区域的现象, 故认为截止到2004年8月, 上述区域不具备强震前地倾斜异常空间配套分布的特征。