Mercury's magnetospheric substorm and storm
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摘要: 磁层亚暴和磁暴是太阳风—行星磁层耦合过程中发生的能量存储和爆发式释放现象,伴随着复杂的等离子体动力学,对磁层以及整个行星都具有强烈的影响. 它们的发生不仅会通过粒子沉降引发绚丽多彩的极光,还可以通过电磁场影响人类以及其他生物的生产生活. 对地球上的亚暴和磁暴现象的描述与研究至今已有近百年的历史,然而对其他行星上的亚暴以及磁暴的研究在本世纪才兴起. 其中,水星和地球在磁层上(尤其是结构以及驱动模式)最为相似,对它的研究可以帮助我们更好地理解亚暴以及磁暴现象的本质,验证或修正原有的空间物理学观点. 随着信使号(MESSENGER)的发射以及入轨探测,长期稳定的磁场、等离子体原位观测数据使得关于水星磁层的深入研究得到长足的发展. 本文回顾了近十余年以来,对于水星磁层亚暴以及磁暴现象的研究进展.Abstract: Magnetospheric substorms and magnetic storms are explosive energy storage and release processes occurring during the interactions between the solar wind and planetary magnetospheres. They are accompanied by complex plasma dynamics processes and they have strong impacts on the magnetosphere as well as on the planet. They are the most well-known space weathering events in Earth's magnetosphere. Their occurrences not only trigger brilliant and colorful auroras through energetic particle precipitation, but also can influence our daily life since intense energetic particles and strong electromagnetic field disturbances are generated. Energetic particles in high latitude ionosphere and magnetosphere are a threat to the satellites in orbit. The strong electromagnetic field disturbances on the high latitude magnetosphere induced by the field-aligned currents can influence and even destroy power and telecommunication infrastructure on the ground. While substorms and magnetic storms on Earth's magnetosphere have been described and studied for nearly a century, the substorms and magnetic storms on other planets have only just started in this century. Among them, Mercury and Earth are the most similar in the aspect of the magnetosphere (especially in structure and driving mode), and the study about magnetospheric substorms and magnetic storms can help us better understand the nature of magnetospheric substorms and magnetic storms, and verify or disprove the theory and explanations derived from the Earth's study. With the launch of MESSENGER and its in-orbit exploration, the long-term in-situ observations of magnetic field and plasma have led to a significant development of the in-depth investigation of Mercury's magnetosphere. In this paper, we review the progress of research on magnetospheric substorms and magnetic storms on Mercury in the last decade.
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Key words:
- Mercury's magnetosphere /
- substorm /
- magnetic Storm
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图 1 水星磁层通量传输事件示例 (修改自 Slavin et al., 2014). (a) 质子能谱 (仪器扫描周期内平均值)和总磁场 (黑色实线). (b)质子能谱 (区分仪器扫描周期)和总磁场(黑色实线). (c) 磁场BZ分量. FTE:通量传输事件;E/q:能荷比;Alt:卫星高度;MLat:卫星磁纬度/(°);LT:地方时
Figure 1. Observations of flux transfer events on Nov 23th, 2011 (modified from Slavin et al., 2014). (a) Proton differential flux with same time step and the magnetic field intensity (black solid line). (b) Proton differential flux with different time step because of FIPS's voltage ramp-up. (c) Magnetic field Z component
图 2 水星磁尾装载—卸载过程示例(修改自Slavin et al., 2010). 自上而下分别是磁场的BX、BY、BZ分量,总磁场强度|B|,磁场与纬向夹角、磁场和经向夹角以及3 s内磁场均方差. 图中MP对应虚线为信使号穿越背阳面磁层顶的时刻,数字标号表示装载事件,Lat B :磁场纬向方位角; Lon B:磁场经向方位角;RMS:均方根
Figure 2. Examples of Mercury's loading-unloading events (modified from Slavin et al., 2010). The first four panels show the magnetic field X, Y, Z component and magnetic field intensity. The following three panels shows the latitudinal angles, longitudinal angles, and root-mean-square deviation (within 3 seconds) of the magnetic field
图 3 水星磁尾亚暴完整过程(修改自Sun et al., 2015a). 左中右对应三个独立的事件,自上而下分别是质子能谱、质子密度、磁场BX、BY、BZ分量、总磁场和磁场俯仰角. PS :等离子体片;LB :磁尾尾瓣区;GR :亚暴增长相;EX:亚暴膨胀相;MLAT:磁纬度;LT:地方时;ALT:高度
Figure 3. Three examples of Mercury's magnetospheric substorm (modified from Sun et al., 2015a). Panels in each column show the proton energy spectrum, magnetic field X, Y, Z component, magnetic field intensity and elevation angle from the top to the bottom. Red dashed lines in the bottom four panels represent the nearest non-substorm time observation. GR: Substorm growth phase; EX: Substorm expansion phase
图 4 水星磁尾强核心场磁通量绳观测(修改自Zhao et al., 2019). (a,b)矢端图;(c~f)磁场BX、BY、BZ分量以及总磁场强度|B|
Figure 4. MESSENGER's observation of magnetotail flux rope with strong core field (modified from Zhao et al., 2019). (a, b) Magnetic field hodograms. (c~f) Magnetic field X, Y, Z components and intensity
图 5 水星磁尾磁通量绳事件的空间分布(修改自Smith et al., 2017). (a) 事件数;(b) 卫星观测时间;(c) 事件发生率;(d) 观测时间随X方向分布;(e) 观测事件随Y方向分布
Figure 5. Spatial distribution of flux ropes event in Mercury's magnetotail (modified from Smith et al., 2017). (a) Event distribution; (b) Observation time in XY plane; (c) Rate of detection; (d) Observation time along X direction; (e) Observation time along Y direction
图 6 一次水星亚暴期间信使号在磁尾观测到的阿尔芬波和压缩波. (a)质子微分通量能谱;(b)质子的观测密度;(c)磁场强度(Bt,黑线),磁场X分量(BX,红线),非亚暴期间最近一次穿越观测到的磁场X分量(虚蓝线);(d)BY;(e)BZ;(f)磁场强度的扰动值;(g)磁场分量的扰动值,δBX(红线)、δBY(绿线)、δBZ(蓝线);(h)局地磁场坐标系下的磁场扰动分量,δBpara(红线)、δBperp1(绿线)、δBperp2(蓝线);(i) 位于16:13:56.0至16:14:07.6间的波动一的磁场矢端分布图;(j) 位于16:14:15.8至16:14:24.0间的波动二的磁场矢端分布图(修改自Sun et al., 2015b)
Figure 6. MESSENGER observations of Alfven waves and compressional waves in Mercury's magnetotail (modified from Sun et al., 2015b). (a) Proton energy spectrum; (b) Proton density; (c) Magnetic field X component (red line) and intensity (black line); (d) Magnetic field Y component; (e) Magnetic field Z component; (f) Residual magnetic field; (g) Residual magnetic field in MSM coordinates; (h) Residual magnetic field in field aligned coordinate; (i) Wave magnetic field hodogram between UT 16:13:56.0 and UT 16:14:07.6; (j) Wave magnetic field hodogram between UT 16:14:15.8 and UT 16:14:24.0
图 7 水星磁尾质子动力学特性分布图(修改自Zhao et al., 2020). (a)质子密度;(b)质子温度;(c)质子热压强;(d) 质子能谱kappa指数;(e) > 0.83 keV质子通量; (f) <0.83 keV 质子通量
Figure 7. Proton kinetic properties in Mercury's magnetotail (modified from Zhao et al., 2020). (a) Proton density; (b) Proton temperature; (c) Proton thermal pressure; (d) Proton kappa index; (e) >0.83 keV proton flux; (f) <0.83 keV proton flux
图 8 水星环电流形态学特征(修改自Zhao et al., 2022). (a) 测试粒子轨迹,两个5 keV 质子从磁尾X=
$ -1.2 \; \mathrm{{R}_{\mathrm{M}} }$ 处出发,初始投掷角分别为50°(红色实线)和130°(蓝色实线);(b) 信使号观测的能量质子(>4.7 keV)在子午面的分布;(c) 赤道面的分布;(d) 晨昏面的分布. 其中观测范围限制在日下点磁层顶距离在1.35~1.49个水星半径之间,对应中等强度太阳风动压Figure 8. Test particle simulation and MESSENGER's observation of Mercury's ring current proton (modified from Zhao et al., 2022). (a) Test particle trajectories of 5 keV proton with 50° and 130°initial pitch angles that released in the midnight magnetotail (X=−1.2 RM). (b~d) MESSENGER's observation of energetic proton (>4.7 keV) distribution in the day-night meridian plane, magnetic equatorial plane, and dawn-dusk meridian plane, respectively. Only magnetosphere crossings with magnetopause subsolar stand-off distances between 1.35 RM and 1.49 RM are taken into account in the above statistics
图 9 基于天基Dst算法推算出的水星地磁Dst指数时间演化图(修改自Zong et al., 2022). 图中①对应“平静状态”,②对应“中等强度磁暴”,③对应“强磁暴”
Figure 9. Time series of Mercury's Dst index that derived from an space-based Dst algorithm (modified from Zong et al., 2022). Circled numbers correspond to the quiet time, moderate magnetic storm time, and intense magnetic storm time, respectively
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