Solar wind controls on Mercury's magnetospheric cusp
Solar wind controls on Mercury's magnetospheric cusp
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DOI：
10.1002/2016ja023687
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发表时间：
2017-04
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影响因子：
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通讯作者：
M. He;J. Vogt;D. Heyner;J. Zhong
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文献类型：
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作者：
M. He;J. Vogt;D. Heyner;J. Zhong
本文利用2848条轨道的水星表面、空间环境、地球化学和测距（MESSENGER）观测资料，综合评估了尖点对太阳风变化的响应。该评估包括四个步骤：（1）提出并验证太阳风磁场的估算方法（2）定义一个指数σ，用于测量在尖点内显著达到峰值的磁扰动的强度，并作为尖点活动水平的指标;（3）通过线性回归，建立了σ随IMF和水星日心距rsun变化的经验模型，（4）利用该模型估算并比较了不同条件下扰动σ的极坐标分布，进行了系统的比较。比较结果表明，当水星位于近日点附近时，在负IMF Bx和负IMF Bz的情况下，尖点附近的扰动峰值最强，范围最广，并在当地时间内延伸。方位角位移与IMF By和rsun两者相关：当IMF By或rsun减小时，尖点向黎明移动。这些依赖性解释的IMF Bx控制的昼侧磁层拓扑结构，组件重联模型应用于IMF的由和Bz，和太阳风冲压压力与日心距离rsun的变化。IMF的组件重联模型的适用性表明，在水星重联发生在较低的剪切角比地球。
This study assesses the response of the cusp to solar wind changes comprehensively, using 2848 orbits of MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) observation. The assessment entails four steps: (1) propose and validate an approach to estimate the solar wind magnetic field (interplanetary magnetic field (IMF)) for MESSENGER's cusp transit; (2) define an index σ measuring the intensity of the magnetic disturbance which significantly peaks within the cusp and serves as an indicator of the cusp activity level; (3) construct an empirical model of σ as a function of IMF and Mercury's heliocentric distance rsun, through linear regression; and (4) use the model to estimate and compare the polar distribution of the disturbance σ under different conditions for a systematic comparison. The comparison illustrates that the disturbance peak over the cusp is strongest and widest extending in local time for negative IMF Bx and negative IMF Bz, and when Mercury is around the perihelion. Azimuthal shifts are associated with both IMF By and rsun: the cusp moves toward dawn when IMF By or rsun decrease. These dependences are explained in terms of the IMF Bx‐controlled dayside magnetospheric topology, the component reconnection model applied to IMF By and Bz, and the variability of solar wind ram pressure associated with heliocentric distance rsun. The applicability of the component reconnection model on IMF By indicates that at Mercury reconnection occurs at lower shear angles than at Earth.