A three-dimensional model study of warm core ring interaction with continental shelf and slope

The interaction of warm core rings with a western wall and shelf/slope is examined with a three-dimensional primitive-equation model. The model ring is initialized with an axisymmetric Gaussian-type anticyclonic eddy placing far from the coastal boundary to allow the ring to freely propagate towards the wall and shelf/slope. The ring initially propagates steadily to the southwest at about 3 km/day under the combined planetary β and nonlinear effects. When colliding with a wall, the ring adjusts into a ‘D’ shape and moves poleward under primarily the image effect. When colliding with a shelf and slope, the ring however becomes stalled and bounces on and off the shelf/slope with little net movement. Small cyclones marked by strong upwelling are generated near the shelfbreak. Cyclones and anticyclones also are spawned at the periphery of the ring. Satellite SST images and concurrent ADCP transects are used to illustrate the strong interaction of a Gulf Stream warm ring (99B) with the Middle Atlantic Bight.     

Combining VLBI and ring laser observations for determination of high frequency Earth rotation variation

Data from the Wettzell ring laser gyroscope are combined with Very Long Baseline Interferometry observations in order to estimate polar motion and Universal Time with hourly resolution. The combination is done at the normal equation level. Data from the period 1 May to 14 October, 2010, are used. We find that the impact of the ring laser data is normally relatively small since presently the accuracy of VLBI is about one order of magnitude better than the accuracy of the ring laser measurements. However, in cases when the accuracy of VLBI is of the order of 1 mas or worse the ring laser improves the accuracy of the estimated parameters, especially for y-pole and Universal Time. For the whole period, the combination on average improves y-pole by 16% and Universal Time by 12% compared to when using only VLBI data.     

A facies model for a quaternary andesitic composite volcano: Ruapehu,New Zealand

Ruapehu composite volcano is a dynamic volcanic-sedimentary system, characterised by high accumulation rates and by rapid lateral and vertical change in facies. Four major cone-building episodes have occurred over 250 Ka, from a variety of summit, flank and satellite vents. Eruptive styles include subplinian, strombolian, phreatomagmatic, vulcanian and dome-related explosive eruptions, and extrusion of lava flows and domes. The volcano can be divided into two parts: a composite cone of volume 110 km³, surrounded by an equally voluminous ring plain. Complementary portions of Ruapehu's history are preserved in cone-forming and ring plain environments. Cone-forming sequences are dominated by sheet- and autobrecciated-lava flows, which seldom reach the ring plain. The ring plain is built predominantly from the products of explosive volcanism, both the distal primary pyroclastic deposits and the reworked material eroded from the cone. Much of the material entering the ring plain is transported by lahars either generated directly by eruptions or triggered by the high intensity rain storms which characterise the region. Ring plain detritus is reworked rapidly by concentrated and hyperconcentrated streams in pulses of rapid aggradation immediately following eruptions and more gradually in the longer intervals between eruptions.     

用中低纬度变化磁场监测磁层环电流强度

本文选择北京地磁台和广州地磁台水平分量时均值的资料,采用Hibberd方法,分析研究了环电流对地磁场夜间值变化的影响,提出一种近似估计环电流强度的简便方法,这种方法可用于及时监测环电流强度的变化,为短期磁暴预报提供有用的资料和途径。     

The bridgman ring paradox revisited

The Bridgman ring experiment, in which a hard rubber ring slipped over a steel rod was observed to split when subjected to a hydrostatic confining pressure, was repeated with Pyrex glass rings. Three cases were studied, in which (a) both ring and rod were unjacketed, (b) the inner wall of the ring was sealed from the pressure medium and (c) both rod and ring were completely jacketed. In the first two cases the ring was observed to split abruptly, with a single axial crack when confining pressure reached a critical level. In the third case no abrupt failure occurred, but a number of axial cracks were found to have formed, grown stably, but not penetrated the outer wall of the ring. The first two cases are explained by hydraulic fracturing of the ring. Observations and analysis indicate that in the third case the cracks started at flaws on the inner surface of the ring and propagated outwards in a stable manner. This case, in which a tensile crack propagates in an all-around compressive stress field, provides some insight into axial cracking of rock in triaxial compression and tensile failure of rock under radial shock loading.     

基态位涡径向分布对浅水涡旋系统动力稳定性的影响分析

本文基于正压浅水模型,分析基态位涡（Potential Vorticity：PV）结构对热带气旋（Tropical Cyclone：TC）类涡旋系统稳定性及其波动特征的影响.通过引入基态PV结构参数：宽度δ（眼墙内外边界涡度发生陡变的半径长度之比）和中空度γ（眼心相对涡度与内核区域平均相对涡度之比）,设计具有相同基流最大切向风速和最大风速半径的170组不同基态PV环结构的敏感性试验,并讨论了不同基态PV结构下涡旋系统最不稳定波数（the most unstable wavenumber：MUWN）和系统最不稳定模态（the most unstable mode of System：MUMS）的特征频率及其不稳定增长率的大小.结果指出：当PV环较宽,系统表现为低波数最不稳定,相应的MUMS为低频波且增长率小;当PV环较窄,系统表现为高波数不稳定,且PV环越实最不稳定波数越高;当PV环窄且空时,MUMS均为中高频波动,且不稳定增长率随PV环的宽度变窄和中空度变空而明显增大.分析典型PV结构下系统演变特征可知,当PV环较宽,MUMS表现为具有平衡约束的低频波动的线性不稳定特征;当PV环趋向窄且空时,MUMS的平衡性约束趋向弱化,同时不稳定增长表现为明显的指数型增长.进一步讨论系统内部非对称结构的形成和传播机制发现,对于弱不稳定的PV环来说,低波数波最不稳定的特征波动具有典型涡旋Rossby波特征;而对于强不稳定的PV环来说,高波数不稳定的特征波动混合波性质明显.     

基于地磁台站数据对磁暴期间环电流和场向电流的分布特征研究

磁暴的发生与环电流的变化密切相关.除了对称环电流外,部分环电流在磁暴的发展过程中也起到了重要的作用,同时部分环电流通过场向电流与极区电离层中的电流形成回路.本文应用INTERMAGNET地磁台网北半球中低纬区域地磁台站数据,对不同强度4个磁暴事件主相和恢复相期间部分环电流和场向电流的磁地方时分布进行了分析和讨论.对于每一个磁暴事件,在低纬地区（地磁纬度约0°—40°N）选用地磁经度上大致均匀的8个台站,通过坐标转换计算平行于磁偶极轴的地磁场水平分量H来分析磁暴期间环电流所引起的磁场扰动;在低纬地区8个台站的基础上增加中纬地区（地磁纬度约40°N—60°N）地磁经度上大致均匀的6个台站,计算地磁坐标系下地磁场东西分量Y来分析磁暴期间场向电流在中低纬地区引起的磁场扰动.结果表明,磁暴主相期间的部分环电流主要作用于磁地方时昏侧和夜侧扇区,并且主相和恢复相期间部分环电流引起的磁场变化随着磁暴级别的增大而增大;磁暴主相期间向下的场向电流多出现在夜侧至晨侧扇区,向上的场向电流多出现在昏侧至午后扇区,且中纬地区向下和向上场向电流的展布范围明显大于低纬地区;恢复相期间弱、中磁暴事件的场向电流呈现与部分环电流相同的减弱趋势,而强、大磁暴事件在恢复相末期场向电流引起的磁场变化明显不同于恢复相的其他时刻,这可能与高纬较强的亚暴活动有关.     

High-frequency noise caused by wind in large ring laser gyroscope data

The large ring laser gyroscope at the Geodetic Observatory Wettzell provides unique data of the rotational component of seismic waves. Wind has been identified as a major source of noise at short periods below 5?min. Strong winds increase the level of detected background noise either through surface friction or through wind load on hill slopes. Since our G ring laser demonstrated a routinely achieved sensitivity for rotations of 10?picorad/s when averaged over 30?s, very small effects become detectable. Using a local finite element model and applying a digital terrain model with 25?m spatial resolution, the effect of local wind forces on tilt and horizontal rotations at the ring laser site was calculated. The transfer of forces by wind ram pressure or surface friction is strongly controlled by the resolution of the terrain model or the land use, respectively. The maximum deformation caused by real wind fields reaches a few tenths of nanorads for both tilt and horizontal rotation. While the tilts are too small to affect the ring laser measurements by a change in its inclination, the horizontal rotations can be detected by the ring laser if the signal builds up within a few seconds or tens of seconds. The comparison of the modelled rotation rate time series with measured ring laser data shows a reasonable agreement in amplitude and waveform, however the correction of the ring laser time series is limited by the crude sampling of the wind measurements.     

不同构造参数对圆环耗能器性能的影响分析

设计了13组不同构造参数的圆环耗能器,采用ABAQUS软件对安装在支撑框架结构中的圆环耗能器进行参数分析,研究圆环钢板厚度、圆环外直径、支撑角度、圆环钢板局部削弱形式和削弱深度对圆环耗能器性能的影响。研究结果表明：圆环耗能器滞回曲线稳定、饱满,塑性耗能能力强;随着圆环钢板厚度的增加或者圆环外直径的减小,圆环耗能器初始刚度和屈服力增大;支撑与横梁之间的角度对圆环耗能器性能有一定影响,交叉支撑角度宜取45°左右;圆环钢板局部削弱圆环耗能器比不削弱圆环耗能器具有更好的耗能效果;圆环钢板局部削弱形式宜采用圆弧式,且钢板削弱深度宜控制在圆环钢板宽度的20%~30%。     

钢铁厂周围不同污染介质的磁学性质及环境意义

为了通过钢铁厂周围不同污染介质的磁学性质研究,实现对环境污染的有效监测,本文系统地采集了河北兴隆和湖南娄底两个钢铁厂周围的树皮和草表面的飞灰、土壤及不同树种的年轮样品.其中前三者用来反映现今污染源,而树木年轮用来追踪长时间尺度的污染历史.通过综合岩石磁学实验分析（包括热磁曲线、磁滞性质和低温实验等）、电子扫描电镜(SEM)和能谱(EDX)以及X射线衍射(XRD)分析,发现钢铁厂周围现今污染源中的主要粗颗粒磁性矿物为磁铁矿、赤铁矿和纯铁.其中8~50 μm的球形磁铁矿颗粒和呈棱角状的铁颗粒是钢铁厂污染物的特征磁性矿物.对不同树种来说,其中香樟树和枫树树木年轮中的磁性矿物以顺磁性物质为主, 不适合用于环境磁学的污染监测.而柳树中的磁性矿物（主要为磁铁矿）与现今污染源的磁性矿物相符.以上研究表明多参数岩石磁学测量并辅以微观分析等手段,可以精确地提取磁性矿物的种类及粒度特征, 判别重工业区污染源,为应用磁学方法来监测环境污染提供依据.     

The shallow plumbing system of Rabaul caldera: a partially intruded ring fault?

The floor of Rabaul caldera experiences complex deformation as revealed both in the geological and historical record, as well as through recent systematic monitoring. The observed deformation pattern has been modelled previously as being caused by tumescent strain above one or more point sources at shallow levels within the caldera block, or as a response of the caldera structure to deeper sources of deformation. Here, two-dimensional finite element modelling is used to re-interpret the pre-1994 eruption deformation data, demonstrating that the observed pattern may have been caused by dykes located in sectors of the ring fault system, as delimited by seismicity. Both a pressurised ring structure and a pair of arcuate sources are modelled. Maximum compressional stress results in a central position within the encompassed block, and a moat-like feature forms offset outwards from the intersection of the azimuth of the modelled deformation sources and the free surface. The modelled deformation generally fits well with the observed movements. That the shallow ring dyke appears not to be complete, existing as two discrete arcuate dykes, helps to explain observed changes in the indicated tilt directions through time. Changing areas of relative down-warping offset outwards from the seismically active ring structure, and north/south-oriented structural up-doming south of Matupit. The distribution of thermal anomalies, and the lack of evidence for shallow central caldera intrusions, can also be explained by this scenario. Associated normal faulting above these dykes, and/or the stress regime generated by simultaneous intrusions into opposite sides of the ring fault, are proposed to explain the apparent inward dip of the intrusions at very shallow levels, leading to the eruptive sites being offset outwards from the seismic zone. A conceptual model is proposed to try to explain the general behaviour of the caldera between 1971 and the eruption of 1994.     

Spatial-Energy Characteristics of Cosmic Rays and Parameters of Magnetospheric Current Systems in March and June 2015

The data from terrestrial observations of cosmic rays at the global network of stations by the method of spectrographic global survey were used to analyze two Forbush decreases during the geomagnetic storms in March and June 2015. The spectra of cosmic ray variations, pitch angle anisotropy of cosmic rays at different phases of Forbush decrease development, and the changes in the planetary system of geomagnetic cutoff rigidities are presented. It is shown that, during the approximation of the spectra of variations by the power function of particle rigidity in the interval of 10–50 GV, the spectrum index is softer at the maximum modulation phase than during the phases of cosmic ray intensity decline and recovery. In the axisymmetric model of the bounded magnetosphere of the Earth, which takes into account the currents at the magnetopause and the ring current, the distance to the subsolar point and the radius of the ring current, as well as the contribution of the ring current to the changes in geomagnetic cutoff rigidity and to the Dst index during the studied events, are determined.     

Geomagnetic activity dependence of O in transit from the ionosphere

Energetic O⁺ ions have important dynamic effects on the ring current. Insights into the effects of O⁺ on ring current dynamics have come primarily from models, not observations. Here, we discuss observations of O⁺ populations escaping from the ionosphere and their access to the plasma sheet and ring current. We review data establishing that a significant flux of O⁺ escapes the ionosphere during geomagnetically quiet intervals. We then estimate the relative magnitude of the O⁺ population in transit between the ionosphere and ring current during quiet intervals before geomagnetic storms. Our analysis suggests that dynamic reconfigurations of the magnetosphere during geomagnetic storms significantly alter the O⁺ transport paths from the ionosphere to the ring current. During these reconfigurations some of the pre-existing, quiet time, in-transit O⁺ populations are captured on magnetic field lines leading to the ring current. The prompt appearance of this O⁺ population in the ring current could modify the evolution of the ring current in the storm growth phase. Our analysis suggests that the consequences of an activity-dependent O⁺ transport path to the ring current should be systematically investigated.     

On the role of collective interactions in asymmetric ring current formation

The contribution of resonant wave-particle interactions to the formation and decay of the magnetospheric ring current is analysed in the framework of a self-consistent set of equations which take into account azimuthal plasmasphere asymmetry. It is shown that the cyclotron interaction of westward drifting energetic protons with Alfven waves in the evening-side plasmaspheric bulge region leads to the formation of a ring current asymmetry located near 18:00 MLT. The time-scale of this asymmetry is determined by the proton drift time through the plasmaspheric bulge and is about 1 - 3 h. A symmetrical ring current decays mainly due to charge exchange processes. The theory is compared with known experimental data on ions and waves in the ring current and on low-latitude magnetic disturbances. New low-latitude magnetometer data on the magnetic storm of 24 - 26 July 1986 are also discussed. The model presented explains the observed localization of an asymmetrical ring current loop in the evening sector and the difference in relaxation time-scales of the asymmetry and the D_st index. It also explains measured wave turbulence levels in the evening-side plasmasphere and wave observation statistics.     

The causal sequence investigation of the ring current ion-flux increasing and the magnetotail ion injection during a major storm

Comprehensive records are available in ENA data of ring current activity recorded by the NUADU instrument aboard TC-2 on 15 May, 2005 during a major magnetic storm(which incorporated a series of substorms). Ion fluxes at 4-min temporal resolution derived from ENA data in the energy ranges 50–81 and 81–158 ke V are compared with in situ particle fluxes measured by the LANL-SOPA instruments aboard LANL-01, LANL-02, LANL-97, and LANL-84(a series of geostationary satellites that encircle the equatorial plane at ~6.6 R_E). Also, magnetic fields measured simultaneously by the magetometers aboard GOES-10 and GOES-12(which are also geostationary satellites) are compared with the particle data. It is demonstrated that ion fluxes in the ring current were enhanced during geomagnetic field tailward stretching in the growth phases of substorms rather than after Earthward directed dipolarization events. This observation, which challenges the existing concept that ring current particles are injected Earthward from the magnetotail following dipolarization events, requires further investigation using a large number of magnetic storm events.     

西门子AR系列CT机的环状伪影分析

本文分析了西门子AR系列CT机的环状伪影的产生原因，除了环境温度湿度变化会引起环状伪影外，如气体探测器（Detector）通道板（Hybrid）以及A/D数据转换板（DAB）等器件的老化和故障是产生环状伪影的主要原因。并且环状伪影的产生还与DAS与球管，准直器（Collimator）之间的相对位置及角度有关。     

On the application of fiber optic gyroscopes for detection of seismic rotations

In recent years, the measurement of rotational components of earthquake-induced ground motion became a reality due to high-resolution ring laser gyroscopes. As a consequence of the fact that they exploit the Sagnac effect, these devices are entirely insensitive to translational motion and are able to measure the rotation rate with high linearity and accuracy over a wide frequency band. During the last decade, a substantial number of earthquakes were recorded by the large ring lasers located in Germany, New Zealand, and USA, and the subsequent data analysis demonstrated reliability and consistency of the results with respect to theoretical models. However, most of the observations recorded teleseismic events in the far-field. The substantial mass and the size of these active interferometers make their near-field application difficult. Therefore, the passive counterparts of ring lasers, the fiber optic gyros can be used for seismic applications where the mobility is more important than extreme precision. These sensors provide reasonable accuracy and are small in size, which makes them perfect candidates for strong motion applications. The other advantage of fiber optic gyroscopes is that if the earthquake is local and shallow (like one occurred early this year at Canterbury, New Zealand), the large ring lasers simply do not have the dynamic range??the effect is far too large for these instruments. In this paper, we analyze a typical commercially available tactical grade fiber optic gyroscope (VG-951) with respect to the seismic rotation measurement requirements. The initial test results including translation and upper bounds of seismic rotation sensitivity are presented. The advantages and limitations of tactical grade fiber optic gyroscope as seismic rotation sensor are discussed.     

波粒相互作用导致环电流质子沉降的卫星共轭观测

波粒相互作用是环电流损失的重要机制之一,但波粒相互作用导致的环电流离子沉降而损失迄今为止缺乏直接的观测证据.基于磁层及电离层卫星的协同观测,本文报道了发生在2015年9月7日,由电磁离子回旋波(EMIC波)导致环电流质子沉降的共轭观测事件.在等离子体层的内边界,Van Allen Probe B卫星观测到,存在EMIC波的区域和不存在EMIC波的区域相比,离子通量的投掷角分布的各向异性变弱.我们将Van Allen Probe B卫星沿着磁力线投影到电离层高度,同时在该投影区域内DMSP 16卫星在亚极光区域观测到环电流质子沉降.而且,通过从理论上计算质子弹跳平均扩散系数,我们进一步证实观测的EMIC波确实能将环电流质子散射到损失锥中.本文的研究工作为EMIC波导致环电流质子沉降提供了直接的观测证据,揭示了环电流衰减的重要物理机制:EMIC波将环电流质子散射到损失锥中,从而沉降到低高度大气层中而损失.     

大磁暴中环电流离子成分的变化及其与磁暴演化的关系

利用CRRES/MICS的观测数据，研究了磁暴期间内磁层离子成分的变化.对1991年两个典型磁暴和12个大磁暴的分析表明，组成暴时环电流的离子可以分成两组，一组由O⁺、低能H⁺和He⁺组成，起源于电离层(IOP)；另一组为高能H⁺和He⁺⁺，主要来自太阳风(SOP).宁静时环电流主要成分为SOP，大磁暴主相极大时环电流的主要成分是IOP.大磁暴期间离子可被注入到很低的高度(L=3-4).IOP对环电流的贡献随磁暴强度增大而增加，在大磁暴主相极大时可达80%(数密度).IOP中O⁺的快速增减是导致Dst指数在磁暴主相期间快速下降和恢复相中快速增长的主要原因.小磁暴中(D_st＞-50nT)O⁺对环电流的贡献可以忽略不计.     

Vertical vibration of ring foundations

A comprehensive analysis is made of the harmonic response of vertically excited, massless, rigid ring foundations supported at the surface of an homogeneous elastic halfspace. The parameters considered include the thickness to radius ratio for the ring, the frequency of the exciting force and of the resulting steady-state response, and Poisson's ratio for the supporting medium. The response quantities examined include the stiffness and damping coefficients of the system in an equivalent spring–dashpot representation of the supporting medium, the displacements of the foundation and of points on the ground surface away from the foundation, and the normal pressure at the foundation–medium interface. The results in each case are compared with those obtained for a solid disk having the same radius as the outer radius of the ring, and a simple approximate model is used to interpret the results and to provide insight into the action of the system. The reported data are computed by a method of analysis that takes due account of the mixed boundary conditions at the surface of the halfspace, and are believed to be of high accuracy.