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The dayside magnetospheric boundary layer at Mercury

机译:水星的日间磁层边界层

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摘要

Magnetic field and plasma data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft on the outbound portions of the first (Ml) and second (M2) flybys of Mercury reveal a region of depressed magnetic field magnitude and enhanced proton fluxes adjacent to but within the magnetopause, which we denote as a dayside boundary layer. The layer was present during both encounters despite the contrasting dayside magnetic reconnection, which was minimal during Ml and strong during M2. The overall width of the layer is estimated to be between 1000 and 1400 km, spanning most of the distance from the dayside planetary surface to the magnetopause in the mid-morning. During both flybys the magnetic pressure decrease was ~1.6 nPa, and the width of the inner edge was comparable to proton gyro-kinetic scales. The maximum variance in the magnetic field across the inner edge was aligned with the magnetic field vector, and the magnetic field direction did not change markedly, indicating that the change in field intensity was consistent with an outward plasma-pressure gradient perpendicular to the magnetic field. Proton pressures in the layer inferred from reduced distribution observations were 0.4 nPa during Ml and 1.0 nPa during M2, indicating either that the proton pressure estimates are low or that heavy ions contribute substantially to the boundary-layer plasma pressure. If the layer is formed by protons drifting westward from the cusp, there should be a strong morning-afternoon asymmetry that is independent of the interplanetary magnetic field (IMF) direction. Conversely, if heavy ions play a major role, the layer should be strong in the morning (afternoon) for northward (southward) IMF. Future MESSENGER observations from orbit about Mercury should distinguish between these two possibilities.
机译:来自水星的第一个(M1)和第二个(M2)飞越部分的水星表面,太空环境,地球化学和测距(MESSENGER)航天器的磁场和等离子体数据显示出磁场强度降低和质子增强的区域磁层顶附近但在其内部的磁通量,我们将其表示为日边界层。尽管白天的磁重新连接形成对比,但在两次相遇期间都存在该层,这在M1期间最小,而在M2期间很强。估计该层的总宽度在1000到1400 km之间,横跨了从早晨的行星表面到早上的磁绝经的大部分距离。在两次飞越期间,磁压下降约为1.6 nPa,内边缘的宽度与质子陀螺动力学尺度相当。内边缘磁场的最大方差与磁场矢量对齐,并且磁场方向没有明显变化,表明磁场强度的变化与垂直于磁场的向外等离子压力梯度一致。由减少的分布观察推断出的层中的质子压力在M1期间为0.4nPa,在M2期间为1.0nPa,表明质子压力估计较低或重离子基本上对边界层等离子体压力有贡献。如果该层是由从尖端向西漂移的质子形成的,则应该有很强的早晨-下午不对称性,该不对称性与行星际磁场(IMF)方向无关。相反,如果重离子起主要作用,则对于北向(南向)IMF,该层应在早晨(下午)增强。未来的MESSENGER从轨道上对水星的观测应该区分这两种可能性。

著录项

  • 来源
    《Planetary and space science》 |2011年第15期|p.2037-2050|共14页
  • 作者单位

    Space Department, The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA;

    Heliophysics Science Division, NASA Goddard Space Flight Center, Creenbelt, MD 20771, USA;

    Space Department, The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA;

    Heliophysics Science Division, NASA Goddard Space Flight Center, Creenbelt, MD 20771, USA,Goddard Earth Sciences and Technology Center, University of Maryland, Baltimore County, Baltimore, MD 21228, USA;

    Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109, USA;

    Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109, USA;

    Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109, USA;

    Space Department, The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA;

    Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    mercury; magnetosphere; boundary layer; magnetic field; plasma; MESSENGER;

    机译:汞;磁层边界层;磁场;等离子体;信使;

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