Strong interplanetary field enhancements at Ulysses—evidence of dust trails' interaction with the solar wind?     

Geraint H Jones  André Balogh  Robert J MacDowall 《Icarus》2003,166(2):297-310

Interplanetary field enhancements were first discovered in the vicinity of Venus. These events are characterised by an increase in the magnitude of the heliospheric magnetic field with a near-symmetrical, sometimes thorn-shaped profile, and last from minutes to hours. Surveys of the events near Venus and Earth indicated clustering of the events in inertial space, which suggested that their sources were Solar System objects other than the Sun. A survey is presented of strong events of this type detected by the Ulysses spacecraft from 1990 to late 2001. Most of the events are accompanied by a discontinuity in the field direction near the events' centres. Other discontinuities are often symmetrical about the enhancement. The majority of events last less than two hours. When examined as a whole, the events tend to be accompanied by subtle changes in some plasma parameters. The majority of the enhancements are accompanied by magnetic holes on their fringes. The enhancements' occurrence rate increases with decreasing heliocentric distance. Possible formation mechanisms are discussed. No link was found with solar, or solar wind sources. Several aspects of the survey results are consistent with an origin related to cometary dust trails. Possible processes associated with a dust-solar wind interaction are discussed.  相似文献   

Capture of dust grains in exterior resonances with planets     

Milo idlichovský  David Nesvorný 《Earth, Moon, and Planets》1995,71(3):175-178

The temporary capture of the dust grains in the exterior resonances with planets is studied in the frames of the planar circular three-body problem with Poynting-Robertson (PR) drag. For the Earth and particles ~ 10 m the resonances 4/5, 5/6, 6/7, 7/8 are shown to be most effective. The capture is only temporary (of order 10⁵ years) and the position of resonance may be calculated from semi-analytical model using averaged disturbing function. These semi-analytical results are confirmed by numerical integration. For various planet this picture changes as with increasing planetary mass the more exterior resonances become more important. We showed that for Jupiter (at least in the space between Jupiter and Saturn) the resonance 1/2 plays the dominant role. The capture time is here several myr but again eccentricity is evolving to eccentricity e ₀ ~ 0.48 of libration point for this resonance.  相似文献   

南向行星际磁场事件与磁暴关系的研究   总被引：5，自引：5，他引：5       下载免费PDF全文

刘绍亮  李立文 《地球物理学报》2002,45(3):297-305

利用172-182年IMP-8飞船的太阳风观测资料和相应地磁活动性指数Dst和AE,研究了43个南向行星际磁场事件期间太阳风和磁层的耦合问题. 与这43个事件对应的地磁暴是中等的和强的磁暴(Dst＜-50nT). 结果表明:(1) 在43个事件中有11个(约占25.6髎)紧随激波之后,18个处于激波下游流场中(占42髎),其余14个(占33髎)和激波没有关连. 绝大多数事件都伴有太阳风动压和总磁场强度的增加;(2) 当行星际晨昏向电场强度EI＞-4mV/m时,只引起磁亚暴,对Dst指数没有明显影响. 仅当EI＜-5mV/m时,磁亚暴和磁暴才会同时出现;(3) 太阳风动压的增加会增强能量向环电流的输入,但不是密度和速度单独起作用,而是以PK=ρV2的组合形式影响能量的输入;(4) 虽然行星际磁场(IMF)南向分量BZ对太阳风和磁层的耦合起着关键作用,但IMF的BX和BY分量相对于BZ的大小对太阳风向磁层的能量传输也有一定影响. 当BX、BY相对BZ较大时能量耦合加强.  相似文献   

Spatial Concentration in Australian Regional Development,Exogenous Shocks and Regional Demographic Outcomes: a South Australian case study     

Peter Smailes  Trevor Griffin  Neil Argent 《The Australian geographer》2016,47(4):527-545

ABSTRACT

As a tribute to the massive contribution of our friend and colleague Graeme Hugo to the population and settlement geography of Australian rural areas, this paper presents a longitudinal study from his home State. It forms part of a wider study of the long-term demographic relationships between Australia’s rapidly growing regional cities and their surrounding functional regions. Of particular interest is the question of what effect the accelerating concentration of population and economic activity into a given regional city will have for the longer term demographic sustainability of its functional region as a whole. Taking the case of Port Lincoln, regional capital of most of South Australia’s Eyre Peninsula, it examines the nature of change in the functional region over the period 1947–2011, and investigates the forces feeding, and partly counteracting, the population concentration process, informed by concepts of evolutionary economic geography. In particular it traces the demographic impact (particularly differential migration and ageing trends) of exogenous shocks to the region’s essentially primary productive economic base during the period of major change from 1981 to 2011.  相似文献   

地球弓激波前的低频磁流体波     

李少峰  孙炜 《地球物理学报》1990,33(2):239-241

一、引言 在地球弓激波前存在着低频磁流体波。这种低频磁流体波是太阳风在地球弓激波上的反射粒子和太阳风粒子之间相互作用产生的。根据人造卫星的观测资料可以得到,在地球弓激波前,Pc3-4脉动频率范围内的低频磁流体波的主频率和行星际磁场强度  相似文献   

行星际空间慢激波的演化          下载免费PDF全文

胡友秋 《地球物理学报》1994,37(3):275-281

日心距离０．３ＡＵ以内形成的磁流体慢激波在向行星际空间传播过程中，通过向上游发出快压缩波而不断减弱．所发出的快压缩波经非线性变陡转化为快激波，形成由原慢激波和新生快激波构成的激波系统．强度不断减弱的慢激波将逐渐演变为准切向间断．这可能是在１ＡＵ附近很少观测到慢激波的重要原因．  相似文献   

1932年昌马地震构造力学特征探讨     

郭万武  张范民 《内陆地震》1994,8(1):75-80

１９３２年昌马地震构造力学特征探讨郭万武，张范民，邢成起，温增平（国家地震局兰州地震研究所，兰州）ＤＩＳＣＵＳＳＩＯＮＯＮＴＨＥＴＥＣＴＯＮＯＭＥＣＨＡＮＩＣＦＥＡＴＵＲＥＳＯＦ１９３２ＣＨＡＮＧＭＡＥＡＲＴＨＱＵＡＫＥＭｓ７．６￥ＧｕｏＷａｎｗｕ；...  相似文献   

激波在磁盔－电流片位场中的传播：（Ⅰ）激波与磁盔间的相互作用          下载免费PDF全文

刘航宇  魏奉思  张剑虹 《地球物理学报》1995,(4)

利用新近获得的子午面磁盔－电流片背景太阳风稳态解，对激波从盔底沿电流片方向往外传播时与磁盔间的相互作用进行了数值模拟研究，重要新结果是：１．磁盔的存在使受扰介质速度跃变中央出现下凹，随着激波传出磁盔区并沿电流片方向传播，速度下凹逐渐减弱以致消失；２．激波将磁盔拉长并把盔顶的环形（垂直赤道面）磁场带到行星际空间，成为行星际磁场南向分量的来源之一；３．５个太阳半径（Ｒ⊙）内的磁盔部分将出现精细结构，沿盔外边界形成两条高速带，以及马蹄形密度（亮）环形结构等．这些结果表明，太阳附近高速等离子体与磁盔间存在重要的动力学相互作用过程，对行星际空间的太阳风三维结构有重要影响．  相似文献   

太阳风流界面的成因          下载免费PDF全文

胡友秋  夏利东 《地球物理学报》1996,39(1):1-6

在日心距离１ＡＵ处的高速流的前沿部位，经常观测到厚度≈１０^４ｋｍ的流界面（ｓｔｒｅａｍｉｎｔｅｒｆａｃｅ）：跨过它密度陡降，温度陡增，风速上升，气压和磁场几乎连续．本文从日心距离０．３ＡＵ处一典型高速流的方位剖面出发，采用二维定态ＭＨＤ模型，研究它在日球赤道面内随日心距离的演化．结果表明，流界面系高速流前沿非线性演化的产物．它先于前、后向激波形成，在日心距离１ＡＵ处得到充分发展，且作为高速流前沿的特征结构之一，可一直延伸到１ＡＵ以远的外日球层．  相似文献   

Spatial distribution of upstream magnetospheric ≥50 keV ions     

G. C. Anagnostopoulos  G. Argyropoulos  G. Kaliabetsos 《Annales Geophysicae》1999,18(1):42-46

We present for the first time a statistical study of 50 keV ion events of a magnetospheric origin upstream from Earths bow shock. The statistical analysis of the 50–220 keV ion events observed by the IMP-8 spacecraft shows: (1) a dawn-dusk asymmetry in ion distributions, with most events and lower intensities upstream from the quasi-parallel pre-dawn side (4 LT-6 LT) of the bow shock, (2) highest ion fluxes upstream from the nose/dusk side of the bow shock under an almost radial interplanetary magnetic field (IMF) configuration, and (3) a positive correlation of the ion intensities with the solar wind speed and the index of geomagnetic index Kp, with an average solar wind speed as high as 620 km s^–1 and values of the index Kp 2. The statistical results are consistent with (1) preferential leakage of 50 keV magnetospheric ions from the dusk magnetopause, (2) nearly scatter free motion of 50 keV ions within the magnetosheath, and (3) final escape of magnetospheric ions from the quasi-parallel dawn side of the bow shock. An additional statistical analysis of higher energy (290–500 keV) upstream ion events also shows a dawn-dusk asymmetry in the occurrence frequency of these events, with the occurrence frequency ranging between 16%-34% in the upstream region.  相似文献