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1.
The evolution of photospheric velocities from the first minutes after the emergence of fresh magnetic flux and the formation
of the first pores in active region NOAA 10488 is studied with a time resolution of 1 min and spatial resolution of 4″. The
emerging magnetic flux of a major active region is initially a bundle of magnetic-flux loops. Some of these loops erupt through
the system of supergranular cells with speeds of up to 1 km/s within 15–25 min and form pores and small spots. It is suggested
that the development of a pore represents the emergence of a horizontal magnetic field, which is converted into elements with
a strong vertical magnetic field. The region of ascending plasma initially coincides with the zero line of a bipolar magnetic
pair. Downflow and upflow regions are related to and appear with the development of pores. During the first hours of their
evolution, the trailing-polarity pores exhibit downflows with mean speeds of ∼500 m/s, while upflows with speeds of ∼250 m/s
dominate near the leading-polarity pores. It is concluded that a matter flow from the leading to the trailing end is present
in the rising loop of a magnetic flux tube, in agreement with well-known numerical-simulation results. The flow that develops
in the magnetic-flux tube erupting through the convection zone persists when pores and small spots emerge in the photosphere,
at least during the first hours of their evolution. 相似文献
2.
The formation of filaments in solar bipolar active regions is investigated, giving particular attention to the relationship between this process and the pattern of supergranular convection. SOHO MDI and Kitt Peak magnetograms and Hα filtergrams are used. The large decaying active region NOAA 8525 is considered over the period May 4–7, 1999. The boundaries of supergranules are identified as concentrations of the line-of-sight photospheric field in magnetograms. Filaments in the central part of the active region are studied; as a whole, they are aligned with the supergranule boundaries. Variations in the magnetic field in this period were manifest primarily in the form of “cancellations” and spatial-redistribution processes consistent with the pattern of developing supergranules. These factors created the conditions necessary for the formation of a filament stretched across the entire active region; i.e., the straightening of the polarity-inversion line and reduction of the horizontal gradients of the magnetic field. One possible explanation of the results is that the magnetic-field component along the filament axis is associated with the vortical structure of horizontal flows in the supergranulation cells. 相似文献
3.
4.
A gradient method for interpreting magnetic anomalies due to horizontal circular cylinders,infinite dykes and vertical steps 总被引：2，自引：0，他引：2
I. V. Radhakrishna Murthy C. Visweswara Rao G. Gopala Krishna 《Journal of Earth System Science》1980,89(1):31-42
A new method of interpreting magnetic anomalies of arbitrarily-magnetised horizontal circular cylinders, dipping dykes and
vertical steps is presented. The method makes use of both horizontal and vertical gradients of the magnetic field of the model
under consideration, rather than the observed magnetic anomaly. Vertical and horizontal gradients are calculated from the
observed anomalies, and plotted one against the other to find out the locus of tip of the resultant gradient vector. This
locus is a symmetrical curve for each of the three models mentioned above. The properties of these curves are used to deduce
the various parameters of these models and the direction of magnetisation. 相似文献
5.
井中磁测仪器距离场源近,磁测资料受到钻孔打穿磁性体产生的内磁场影响,往往存在强干扰压制有用信号,因此研究井中磁测资料预处理与弱信号识别方法具有重要意义。笔者将地面重磁资料边界识别中倾斜角总水平导数和解析信号振幅方法改进后应用于井中磁测资料预处理中,提出倾斜角垂向导数和均值归一解析信号振幅方法。通过模型分析证明了两种方法都可识别强弱不同的井旁磁性体位置,反映边界信息,且给出了计算均值归一解析信号振幅过程中窗口选择的依据。将两种方法应用于江苏某工区ZK002孔磁测资料预处理中,得出倾斜角垂向导数方法应用于实测资料中会放大干扰,而均值归一解析信号振幅方法增强了该钻孔弱异常信息,且压制了干扰信号,处理结果与磁化率测井和钻孔资料相对应。 相似文献
6.
航磁异常深部弱信号提取技术研究 总被引：1，自引：0，他引：1
磁异常通常是地下不同深度磁性地质体产生磁场的叠加,在规范高度的航磁测量结果中,深部磁性体所产生的异常通常表现为弱而平缓,其水平与垂向分辨率均较低,在航磁资料处理解释中难以有效捕获。因此,应用适当方法提取由深部地质体引起的弱磁信息是十分必要的。本文采用精度高且稳定的位场延拓技术将航磁异常向下延拓,可以稳定增强磁异常幅度,随着延拓面与场源之间距离的减小,浅成磁信号与深成磁信号的视深度差异将增大,在对数功率谱上可以将其区分,而后可利用匹配滤波方法将浅部信号剥离,从而得到深部弱信号,同时可计算深部弱信号的视深度。 相似文献
7.
以鲁甸地震诱发的红石岩崩塌滑坡为研究对象,通过大型振动台模型试验和3DEC数值模拟,研究了含软弱岩层的反倾岩质边坡的动力响应和破坏失稳模式.研究结果表明:水平加载下,随频率增大PGA放大系数先减小后增大,在接近坡体自振频率8Hz的波形加载下,坡体动力响应最为剧烈,软弱岩层对不同频率的横波具有放大和吸收作用,对5~10Hz的横波放大效应明显,对15~20Hz的横波则明显吸收;竖向加载下,随加载正弦波频率的增加,PGA放大系数先增大,25Hz时PGA放大系数减小,随后又继续增大,在频率为30Hz时PGA放大系数达到最大,在5~30Hz范围内软弱岩层对纵波均具有一定的放大效果;双向加载下,坡体水平和竖向PGA放大系数分布与单向加载一致,但双向加载下坡体部分位置动力响应加剧,部分位置动力响应则受到抑制.含软弱岩层的反倾岩质边坡破坏过程可以分为6个阶段:坡体内部轻微损伤-软岩挤出、软硬岩交界上方硬岩拉裂-硬岩裂纹向上延展-软弱岩层挤压滑动-层面和纵向节理贯通形成滑面-边坡破坏.在软弱岩层的反倾岩质边坡中,软弱岩层具有对地震波的放大吸收、折射反射作用,影响着边坡的动力响应特征,软弱岩层的挤出破坏导致上部岩体岩结构面松动开裂,是该类岩质边坡破坏发展的主要原因,对该类边坡需应注意对软弱岩层进行加固防护,减小边坡的动力破坏. 相似文献
8.
目前井中磁测解释大都采用水平矢量图指向确定矿体的方法,但由于磁场水平分量的定向问题,致使仅使用水平分量矢量对磁性体解释常会出现错误结果。通过描述水平产状与倾斜产状磁性体的磁场特征,对磁性体表面不同位置磁异常垂直分量及水平分量差异进行了说明,通过三个实例对反映在磁性体上、下位置的垂直分量与水平分量磁异常的空间分布特征进行了具体描述,并利用井中磁测曲线有效地解决了井底及井旁磁性体的赋存情况。多年来的工作实践证明,使用磁异常场垂直分量及水平分量特征,能准确的判定磁性矿体的主体方向及产状,该解释方法的推广有利于寻找深部磁性矿体。 相似文献
9.
K. N. Mitrofanov V. I. Krauz V. V. Myalton V. P. Vinogradov A. M. Kharrasov Yu. V. Vinogradova 《Astronomy Reports》2017,61(2):138-152
The results of laboratory simulations of astrophysical jets are presented. Plasma flows generated in the PF-3 plasma-focus installation of the NRC “Kurchatov Institute” and propagating to distances substantially exceeding their transverse dimensions are studied. It is shown usingmagnetic probes that the plasma flow propagates with a frozen-in magnetic field. The resulting radial distribution of the azimuthal magnetic field corresponds well to the distribution created by a longitudinal current of ~10 kA flowing in a region with a radius of 1–2 cm near the axis. Structures associated with return currents are observed at the periphery of the flow. The magnetic field decays rapidly as the flow propagates along the axis. Nevertheless, the leading lobe of the plasma flow is preserved to substantial distances in a neon discharge, possibly due to radiative cooling of the plasma. 相似文献
10.
柬埔寨王国位于低纬度地区,地质勘查程度较低,地面高精度磁测技术能够快速获取磁异常信息,进行找矿评价。在低纬度地区磁化方向主要以水平磁化为主,磁性体产生的磁异常以负磁异常为主。本文通过对柬埔寨王国Mesam金矿磁测数据进行倒相180°、化赤和低纬度化极处理对比,认为三种处理方法得到的结果都能够完整地反映磁场分布特点,在不能忽略剩磁影响的低纬度地区对实测数据进行低纬度化极后再进行解释更加贴近真实且细节更加丰富。通过对低纬度化极后的磁异常进行水平总梯度模和小波多尺度分解计算等位场异常处理,认为磁异常水平总梯度模计算能够较好地反映深部地质体的边界范围,小波多尺度分解计算能够提取特定深度地质体的空间信息,在该区选取的磁异常处理技术是有效的,为进一步扩大该金矿区远景储量提供了新的思路。 相似文献
11.
A small-scale hydrogeological study was conducted in a fractured carbonate-rock aquifer located in a quarry to relate groundwater flow to the fracture network. The field study in the St-Eustache quarry, which integrates structural surveys, well logging and hydraulic tests, showed that the most important features that affect groundwater flow in the sedimentary aquifer are high hydraulic conductivity horizontal bedding planes. Vertical fractures are abundant in the quarry and throughout the region, but they have a minor effect on groundwater flow. To have a significant impact on the flow regime and lead to vertical groundwater flow, the permeability of all vertical joints need to be enhanced compared to what was generally observed at the site. Such an increase in permeability could potentially occur where dissolution and fracturing is more intense or at stress release locations such as near the surface in the quarry. 相似文献
12.
康定MS6.3级地震斜坡地震动响应监测分析 总被引：1，自引：0，他引：1
芦山MS7.0地震、鲁甸MS6.5地震诱发了大量的次生山地灾害,一些学者认为地形放大效应是其中的一个影响因素,但目前斜坡地震动响应研究仍然缺乏大量的实测数据支撑。通过在冷竹关两岸斜坡不同部位掘进平硐并放置强震监测仪器的方法,对沟谷两岸斜坡地震动响应特征进行研究,剖面较为完整地记录了康定地震两岸斜坡的地震动响应特征。监测数据揭示,(1)相对于康定姑咱参考站,位于右岸半岛状凸出山梁顶部1#监测点的水平和竖直向PGA放大系数分别达到了10.6～11.5、7.1,阿里亚斯强度最大,水平东西向比竖直向HVSR频比值达到11.1,卓越周期在低频部分;位于右岸山梁中部2#监测点水平和竖直向PGA放大系数分别达到了4.3～5.0、2.3;(2)左岸地形坡面起伏较小,记录的峰值加速度较小,仅在坡折部位5#监测点有明显的放大,水平与垂直峰值加速度放大系数分别为3.0～4.5、2.3,各监测点频比存在多个卓越周期,其放大效应在高频段更突出;(3)近直线型斜坡内(6#及7#监测点)放大效应相对较弱,且监测洞外侧放大系数大于水平深度较大的内侧。结果表明冷竹关两岸斜坡存在明显的地形放大效应,且右岸半岛状凸出山脊地形较左岸中高山斜坡地形放大效应显著。对比芦山地震该剖面放大系数,揭示了背坡面效应。 相似文献
13.
以漳州招银高速MK10+250段含软弱夹层岩质边坡的锚框支护工程为原型,设计了1/30缩尺模型边坡,开展了20种工况的模拟地震动试验,重点关注坡体高程、地震动幅值对PGA放大系数和PEP震荡系数的影响。坡内和坡面各测点处PGA放大系数,均呈现出明显的高程效应;但由于软弱夹层的隔震作用和锚框支护的加固作用,使得边坡加速度响应更趋于整体性,不表现出明显的鞭梢效应。坡内和坡面各测点处PGA放大系数,随着输入地震动幅值的增大呈线性减小或指数型减小。各测点处PEP震荡系数随埋深增大呈近似线性增加,随地震动幅值增大呈非线性增加;并且在高烈度工况下,指向坡外方向的附加水平压力大于指向坡内方向。通过对边坡表观破坏特征的描述,发现表观破坏主要集中在软弱夹层上部坡体中,尤其是坡顶表层出现了贯通裂缝;但由于锚索-框架支护的加固作用,其边坡并未沿软弱夹层发生整体性失稳。 相似文献
14.
Radia El Gout Driss Khattach Mohammed-Rachid Houari Touria Chennouf 《Arabian Journal of Geosciences》2011,4(1-2):299-308
From a geologist's perspective, magnetic data are most useful in mapping contacts and providing insight into the 3D geometry of the geology. Since the early 1970s, automatic methods based on the horizontal and vertical derivatives are applied to potential field data in order to map geological lineaments. In this paper, three methods for locating magnetic contacts are applied to magnetic anomaly data of the study area. The local maxima of horizontal gradient determined on the magnetic map and its upward continued maps to several heights delineate the contacts and indicate their dips. The amplitude of the 3D analytic signal of magnetic data provides information on the location of the edge of the sources in both the horizontal and vertical dimensions. The Euler deconvolution is also used to estimate the source depth at the contact location. These results allow the production of a structural map showing the magnetic lineaments for the survey area. This map is consistent with many faults already recognised or supposed by the traditional structural studies and highlights new ones by specifying their layout and dips. 相似文献
15.
Observations of the large-scale solar magnetic field (synoptic maps) and measurements of the magnetic field of the Sun as a star (the total magnetic field) are used to determine the dipole magnetic moment and direction of the dipole field for three successive solar cycles. Both the magnetic moment and its vertical and horizontal components vary regularly during the cycle, but never disappear completely. A wavelet analysis of the total magnetic field shows that the amplitude of the 27-day variations of this field is very closely related to the magnetic moment of the horizontal dipole. The reversal of the global dipole field corresponds to a change in the inclination of its axis and occurs in a series of steps lasting one to two years rather than continuously. Before the onset of the reversal, the dipole axis precesses relative to the solar rotational axis, then shifts in a meridianal plane, reaching very low latitudes, where a substantial shift in longitude then begins. These results are discussed in connection with helioseismological data indicating the existence of oscillations with a period of about 1.3 yr and properties of dynamo processes for the case of an inclined rotator. 相似文献
16.
The structure and magnitude of the electric field created by a rotating accretion disk with a poloidal magnetic field is found for the case of a vacuum approximation along the axis. The accretion disk is modeled as a torus filled with plasma and a frozen-in magnetic field. The dimensions and location of the maximum electric field as well as the energy of the accelerated particles are found. The gravitational field is assumed to be weak. 相似文献
17.
考虑场地效应的高陡岩质斜坡地震失稳机制 总被引：2，自引：0，他引：2
以金沙江乌东德水电站右岸的鸡冠山梁子高陡斜坡为典型实例,在斜坡表层地震动监测基础上,通过在斜坡弹性模型底部分别输入水平、竖向Ricker子波,发现：斜坡顶部低模量岩体材料在水平Rick子波激励下,易产生放大效应;而当输入竖向Rick子波时,易在模型表层地形凸起部位产生共振放大,其顶面表层卓越频率也与现场实测值基本一致。其次,对比分析了在分别输入汶川八角什邡加速度记录、典型鲁甸地震加速度记录时的斜坡弹塑性模型的稳定性和动力响应特征,发现：（1）斜坡在静力条件下可能存在3种不同位置潜在滑面,但输入两种地震波后,变形破坏区仅发生在顶部滑面位置;（2）输入汶川地震波时,斜坡顶部滑面剪应变增量明显大于输入鲁甸地震波时对应值,且前者的滑面出现明显整体拉破坏区,滑面上部水平、竖向残余变形也不收敛,处于震后斜坡失稳状态。后者滑面底部无明显的拉破坏区,滑面上部残余变形收敛,处于震后斜坡稳定状态;（3）斜坡水平、竖向加速度都在斜坡顶部低模量材料表层出现明显的放大现象,场地效应明显。此外,表层加速度普遍大于斜坡内部相应值,尤其是地形凸起位置。输入汶川地震波时斜坡顶部水平向加速度放大系数大于鲁甸地震波相应值,但竖向加速度放大系数两者基本一致。 相似文献
18.
分析了水平电偶源与垂直磁偶源的电磁场在半空间大地中的分布特点,指出观测各场分量的合适地面部位。为了定性解释,一般将场分量计算为单分量视电阻率或比值视电阻率;做定量解释时,可直接采用场强进行反演,以减小换算误差。基于当前电偶源与磁偶源的发射功率和电磁场衰减规律,在实际应用中,水平电偶源可探测更大深度(<3 000 m),垂直磁偶源探测浅部(<500 m)。 相似文献
19.
Large-scale shaking table model tests were carried out to study the dynamic behaviors of slopes and failure mechanism of landslide in permafrost regions. The model slope was constituted of silty clay layer stacked on an ice layer with 8° surface slope. Acceleration, displacement, and pore pressure were measured subjected to vertical and horizontal seismic loadings. The horizontal wave has a stronger influence on the failure of the model than the vertical wave motion, and the natural frequency of vibration in the horizontal direction decreased obviously at the failure state. The model slope has three components of different nonlinear mechanical properties, which are the soil layer, soil-ice interface, and ice layer. The amplification factor of peak ground acceleration is obviously smaller at the soil-ice interface than that at the soil and ice layer. The acceleration responses are nonlinear because of the nonlinear soil properties and degradation of modulus with increasing horizontal acceleration. Especially, excess pore pressure generation was observed near the soil-ice interface of the slope subjected to higher input acceleration, which resulted in the decrease of the effective stress. Failure surface appeared to be the soil-ice interface, which was consistent with the field observations of landslides in permafrost regions. Slope failure could be defined based on the massive movement of the slope, characterized by integral sliding pattern along the soil-ice interface without the distinct deformation inside the sliding body. The results show that the sliding of the slope with soil layer at gentle gradient is mainly triggered by the combined action of horizontal seismic wave, existence of soil-ice interface, and pore pressure generation in permafrost regions. 相似文献
20.
SOHO-MDI daily magnetic field synoptic data (a 14-year series of daily maps of the solar magnetic field intensity B available at the site ) have been used to analyze the dynamics of the photospheric magnetic field in the vicinity of the solar equator. The standard
deviation s
B
of the field B calculated over areas of tens of square degrees on the solar disk was taken as a basic index. An 11-year variation similar
to that observed at higher latitudes is observed in the vicinity of the equator, and is similar for weak and strong fields;
i.e., the solar cycle exists in the sunspot-free zone. New qualitative data support the idea that the weak background magnetic
field increases toward the solar limb. This angular dependence suggests the existence of a transverse component of the background
field. The magnetic fields in the vicinity of the equator were significantly different in the initial phases of Cycles 23
and 24. Annual variations of s
B
were observed near the center of the solar disk. These variations are due to two factors: the annual variation of the distance
from the equator to the disk center and the increase of s
B
with with distance from the equator. Reliable detection of these variations is an evidence of high accuracy of the s
B
estimates. 相似文献