• ISSN 2096-8957
  • CN 10-1702/P

日球层等离子体片及其行星空间天气效应

洪一纯 郭建鹏 赵丹

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日球层等离子体片及其行星空间天气效应

A review of heliospheric plasma sheets and their impacts on planetary space weather

    Corresponding author: Guo Jianpeng, jpguo@bnu.edu.cn ;
  • CLC number: P353.8

  • 摘要: 日球层等离子体片是出现在日球层电流片附近的等离子体结构,具有离子数密度明显增强、磁场总强度下降、等离子体β增大等特征,是行星际扰动和行星空间天气的重要驱动源,被广泛关注和研究. 日球层等离子体片内可能存在局地电流片、等离子体波动和磁岛,也引起日趋深入的讨论. 本文简要介绍有关日球层等离子体片的一些研究进展,重点关注日球层等离子体片的源区、成因、就地观测特征和行星空间天气效应,并尝试分析一些值得探讨的科学问题.
  • 图 1  STA卫星在2007年4月17日观测到的日球层等离子体片包围着日球层电流片事例. 从上到下,依次是超热电子投掷角分布、磁场方位角ϕB、等离子体数密度Np以及太阳风速度Vp. 图中垂直的黑线是日球层电流片的位置,阴影区是日球层等离子体片(修改自黄佳,2017

    Figure 1.  STEREO A data of the HCS surrounded by HPS event observed on 17 April 2007. The four panels show (from top to bottom) the pitch angle distribution of suprathermal electrons, the phi angle of the interplanetary magnetic field ϕB, the proton density Np, and the solar wind speed Vp. The solid vertical line marks the HCS, and the shaded region indicates the HPS (modified from Huang, 2017)

    图 2  一个理想冕流和它的“茎梗”(纬度范围约1°~2°),它们延伸至行星际空间形成日球层等离子体片(修改自Bavassano et al., 1997

    Figure 2.  Schematic of an idealized coronal streamer and its stalk (The latitude range is about 1°~2°), which forms the heliospheric plasma sheet in interplanetary space (modified from Bavassano et al., 1997)

    图 3  盔冕流顶部高β等离子体(灰色区域)通过开放磁力线和闭合磁力线之间的交换磁重联释放,从而形成日球层等离子体片(修改自Wang et al., 2000; Crooker et al., 2004

    Figure 3.  Schematic of high-beta plasma release (shaded parcel) by interchange reconnection near the cusp of a helmet streamer and the resulting field inversion with localized current sheets (dotted lines) (modified from Wang et al., 2000; Crooker et al., 2004)

    图 4  盔冕流核心区的等离子体从闭合磁力线挤出去,在盔冕流顶部两侧冕流沿着日球层电流片发生剪切,产生等离子体团A和B,从而形成日球层等离子体片(修改自Suess et al., 2009

    Figure 4.  Schematic of high-beta plasma sheet release from the streamer core, carrying loops of magnetic flux, and being sheared along the HCS (modified from Suess et al., 2009)

    图 5  通过磁场重联产生小等离子体团物理图像.(a)磁力线中性线所在平面;(b)垂直磁力线中性线的平面. 灰色阴影区表征高β的小等离子体团. 黑线表征日球层电流片周围的磁力线. 虚黑线表征磁绳附近区域的磁力线结构. 黑线表征的贯穿磁绳的磁力线,一端连接太阳;红虚线代表的磁力线,两端连接太阳. 图(a)、(b)中的蓝线磁力线,源于小等离子体团,围绕磁绳,并不连接太阳. 图(b)中的橙色箭头表征盔冕流顶部的系列磁重联X线入流;蓝色小箭头表征磁重联X线出流(修改自Sanchez-Diaz et al., 2019; Lavraud et al., 2020

    Figure 5.  Sketch of magnetic reconnection as the origin of blobs in (a) a plane containing the neutral line and (b) a plane perpendicular to the neutral line. The gray areas indicate the location of the highest-β regions (or blobs). The black lines represent the magnetic field lines around the HCS. The dashed black lines represent the magnetic field lines structure in the vicinity of the flux ropes. While the black magnetic field lines that thread through all the flux ropes are constructed here such that they have only one end attached to the Sun, the red dashed line is meant to highlight that there can exist other configurations such that both ends may be connected to the Sun. Finally, the blue lines in panels (a) and (b) show the magnetic field lines from the high-β blobs, which surround the flux ropes, and that are typically disconnected from the Sun. The orange arrows in panel (b) show the inflows of magnetic reconnection at the X-lines formed by sequential magnetic reconnection at the tip of the helmet streamer. The small blue arrows in panel (b) show the exhaust velocities away from each X-line (modified from Sanchez-Diaz et al., 2019; Lavraud et al., 2020)

    图 6  日球层等离子体片扫过地球时,动压脉冲压缩磁层的向阳侧. 圆点表征电子(蓝色)和质子(黑色). 由于日球层等离子体片压缩磁层,垂直磁场方向的粒子数密度和温度会增大(修改自Tsurutani et al., 2016

    Figure 6.  A schematic of a solar wind pressure pulse compressing the outer portion of the dayside magnetosphere. The dots represent electrons (blue) and protons (black). The particle densities and the temperatures perpendicular to the magnetic field are enhanced by the magnetospheric compression due to the solar wind HPS impingement (modified from Tsurutani et al., 2016)

    图 7  MAVEN在2015年3月7日至11日期间观测到的一个日球层等离子体片嵌入在行星际日冕物质抛射的鞘区中. 从上至下:MAVEN探测器高度,行星际磁场强度,MSO坐标下的磁场方向仰角和方位角,太阳风速度,密度,温度和由观测速度计算得到的预期温度(红色曲线),质子β,离子能谱,电子能谱,电子投掷角分布(~282 eV),太阳高能离子和电子能谱. 两条垂直的红色虚线表征行星际日冕物质抛射的边界,垂直的黑色虚线表征由行星际日冕物质抛射驱动的激波. 阴影区域表征日球层等离子体片(修改自Zhao et al., 2021

    Figure 7.  MAVEN observations of an HPS embedded within the sheath region of an interplanetary coronal mass ejection (ICME) during 2015 March 07-11. From top to bottom: the MAVEN spacecraft altitude, interplanetary magnetic field strength, elevation angle and azimuthal angle of magnetic field direction in MSO coordinates, solar wind velocity, density, SWIA temperature overlaid with the expected temperature (red dotted curve) from the observed velocity, proton β, ion energy spectra, electron energy spectra, pitch angle (PA) distributions of electron (~282 eV), SEP ion and electron differential flux spectra. Two vertical red dashed lines bound an ICME and the vertical black dashed line mark a shock driven by the ICME. The shaded region indicates the HPS interval (modified from Zhao et al., 2021)

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  • 收稿日期:  2021-04-04
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日球层等离子体片及其行星空间天气效应

摘要: 日球层等离子体片是出现在日球层电流片附近的等离子体结构,具有离子数密度明显增强、磁场总强度下降、等离子体β增大等特征,是行星际扰动和行星空间天气的重要驱动源,被广泛关注和研究. 日球层等离子体片内可能存在局地电流片、等离子体波动和磁岛,也引起日趋深入的讨论. 本文简要介绍有关日球层等离子体片的一些研究进展,重点关注日球层等离子体片的源区、成因、就地观测特征和行星空间天气效应,并尝试分析一些值得探讨的科学问题.

English Abstract

    • 最早观测到行星际磁场扇区结构时,研究人员并不清楚扇区边界的物理本质(Ness and Wilcox, 1964; Wilcox and Ness, 1965). Coleman等(1966)最早提出扇区与冕流相关的观点. 随后,扇区边界这个概念就被物理图像更加明晰的日球层电流片(Heliospheric Current Sheet, HCS)替代. 日球层电流片是太阳磁场中性线向行星际空间中的延伸(Schulz, 1973),是太阳磁力线在行星际空间发生极性翻转的界面(Gosling et al., 1981). 在太阳活动低年,日球层电流片相对扁平,呈芭蕾舞裙形状;在太阳活动高年,日球层电流片倾斜,呈海螺壳形状(Badruddin et al., 2007; Riley et al., 2012). 位于黄道面附近的卫星穿越日球层电流片,会观测到磁场方位角发生~180°跃变. 此外,还可能在数分钟或数小时之内观测到磁场极性多次跳变. 后一种情形通常与磁力线弯折或磁场重联(包括交换磁重联)相关(Crooker et al., 2004; Huang et al., 2016). 为了准确判定日球层电流片位置,除了磁场观测,往往还需要结合超热电子观测. 超热电子源于太阳并沿着磁力线向外运动,它们形成的束流主要集中在0°或180°投掷角上. 当观测到超热电子的投掷角发生~180°跃变时,可判断磁力线的极性翻转(Gosling et al., 1987). 卫星穿越日球层电流片时,通常在日球层电流片附近观测到一个质子数密度明显增强、磁场总强度下降(部分情形)、等离子体β增大的区域,即日球层等离子体片(Heliospheric Plasma Sheet, HPS)(Burlaga et al., 1990; Crooker et al., 1993, 1996, 2004; Winterhalter et al., 1994; Bavassano et al., 1997; Wang et al., 1998, 2000; Liu et al., 2014). 部分日球层等离子体片包围着日球层电流片,还有部分日球层等离子体片则出现在日球层电流片边缘(Crooker et al., 2004; Suess et al., 2009; Liu et al., 2014). 图1显示STEREO A卫星(简称STA)在2007年4月17日观测到日球层等离子体片包围着日球层电流片的一个实例. 一般认为日球层等离子体片起源于盔冕流区域 (Gosling et al., 1981, Steiger et al., 1995, Bavassano et al., 1997).

      图  1  STA卫星在2007年4月17日观测到的日球层等离子体片包围着日球层电流片事例. 从上到下,依次是超热电子投掷角分布、磁场方位角ϕB、等离子体数密度Np以及太阳风速度Vp. 图中垂直的黑线是日球层电流片的位置,阴影区是日球层等离子体片(修改自黄佳,2017

      Figure 1.  STEREO A data of the HCS surrounded by HPS event observed on 17 April 2007. The four panels show (from top to bottom) the pitch angle distribution of suprathermal electrons, the phi angle of the interplanetary magnetic field ϕB, the proton density Np, and the solar wind speed Vp. The solid vertical line marks the HCS, and the shaded region indicates the HPS (modified from Huang, 2017)

      本文简述日球层等离子体片的相关研究进展:(1)日球层等离子体片的源区和成因;(2)日球层等离子体片的观测特征;(3)日球层等离子体片的行星空间天气效应;尝试分析一些值得探讨的科学问题.

    • 在日球层电流片附近观测到日球层等离子体片,便引发一个思考:日球层等离子体片的源区在哪里?它们是如何形成的?

      Borrini等(1981)分析阿尔法粒子丰度(Nα/Np)极低的太阳风等离子体观测数据时,发现这部分等离子体具有磁场极性翻转、密度高、速度低等特征,并进一步通过叠加分析的方法确定了低Nα/Np位于日球层电流片的附近区域(Nα代表太阳风阿尔法粒子数密度,Np代表太阳风质子数密度). Gosling等(1981)将太阳风观测映射至太阳上,发现高密度、低Nα/Np且伴随磁场极性翻转的等离子体通常对应盔状冕流带. Bavassano等(1997)研究太阳神2号(Helios 2)探测器在0.3~1.0 AU观测到的日球层等离子体片,发现低Nα/Np出现在日球层等离子体片的边界处,认为日球层等离子体片源于盔冕流的核心区,冕流的“茎梗”延伸至行星际形成日球层等离子体片,物理图像简单直观(见图2,图中密度的路径积分计算公式为$\int {n{\rm{d}}s} $n表示等离子体数密度). Wang等(2000)Crooker等(2004)认为日球层等离子体片的源区位于盔冕流区,在盔冕流顶部区域开放磁力线和闭合磁力线之间发生交换磁重联,不连续地释放高β等离子体团,同时产生局地电流片,其物理图像见图3. 释放的等离子体团便形成了日球层等离子体片. 这一观点已被普遍接受为日球层等离子体片形成的可能情形之一. 还有一种观点认为盔冕流核心区的等离子体是从闭合磁力线挤出去,然后再被冕流两侧的速度差剪切成两部分(Suess et al., 2009),其物理图像见图4. 这一观点可以解释日球层等离子体片常出现在日球层电流片的两侧.

      图  2  一个理想冕流和它的“茎梗”(纬度范围约1°~2°),它们延伸至行星际空间形成日球层等离子体片(修改自Bavassano et al., 1997

      Figure 2.  Schematic of an idealized coronal streamer and its stalk (The latitude range is about 1°~2°), which forms the heliospheric plasma sheet in interplanetary space (modified from Bavassano et al., 1997)

      图  3  盔冕流顶部高β等离子体(灰色区域)通过开放磁力线和闭合磁力线之间的交换磁重联释放,从而形成日球层等离子体片(修改自Wang et al., 2000; Crooker et al., 2004

      Figure 3.  Schematic of high-beta plasma release (shaded parcel) by interchange reconnection near the cusp of a helmet streamer and the resulting field inversion with localized current sheets (dotted lines) (modified from Wang et al., 2000; Crooker et al., 2004)

      图  4  盔冕流核心区的等离子体从闭合磁力线挤出去,在盔冕流顶部两侧冕流沿着日球层电流片发生剪切,产生等离子体团A和B,从而形成日球层等离子体片(修改自Suess et al., 2009

      Figure 4.  Schematic of high-beta plasma sheet release from the streamer core, carrying loops of magnetic flux, and being sheared along the HCS (modified from Suess et al., 2009)

      帕克太阳探测器(Parker Solar Probe, PSP)抵近太阳探测,为进一步探究日球层等离体片的成因提供了重要机遇. 在第一次轨道(距日0.165 AU)运行中,PSP观测到盔冕流顶部通过一系列磁重联过程释放出的小等离子体团和磁绳结构. Lavraud等(2020)分析认为日球层等离体片本质上是盔冕流顶部发生的一次大尺度磁重联过程的耗散区,也即高离子密度区. 在耗散区内发生一系列磁重联,产生一连串的小等离子体团和磁绳结构,物理图像见图5. 在这个物理图像中,绝大部分日球层等离体片之间是间断的,且均是通过盔冕流顶部的磁重联产生,不同于通过交换磁重联间歇性地释放等离子体团,进一步丰富了日球层等离体片的成因.

      图  5  通过磁场重联产生小等离子体团物理图像.(a)磁力线中性线所在平面;(b)垂直磁力线中性线的平面. 灰色阴影区表征高β的小等离子体团. 黑线表征日球层电流片周围的磁力线. 虚黑线表征磁绳附近区域的磁力线结构. 黑线表征的贯穿磁绳的磁力线,一端连接太阳;红虚线代表的磁力线,两端连接太阳. 图(a)、(b)中的蓝线磁力线,源于小等离子体团,围绕磁绳,并不连接太阳. 图(b)中的橙色箭头表征盔冕流顶部的系列磁重联X线入流;蓝色小箭头表征磁重联X线出流(修改自Sanchez-Diaz et al., 2019; Lavraud et al., 2020

      Figure 5.  Sketch of magnetic reconnection as the origin of blobs in (a) a plane containing the neutral line and (b) a plane perpendicular to the neutral line. The gray areas indicate the location of the highest-β regions (or blobs). The black lines represent the magnetic field lines around the HCS. The dashed black lines represent the magnetic field lines structure in the vicinity of the flux ropes. While the black magnetic field lines that thread through all the flux ropes are constructed here such that they have only one end attached to the Sun, the red dashed line is meant to highlight that there can exist other configurations such that both ends may be connected to the Sun. Finally, the blue lines in panels (a) and (b) show the magnetic field lines from the high-β blobs, which surround the flux ropes, and that are typically disconnected from the Sun. The orange arrows in panel (b) show the inflows of magnetic reconnection at the X-lines formed by sequential magnetic reconnection at the tip of the helmet streamer. The small blue arrows in panel (b) show the exhaust velocities away from each X-line (modified from Sanchez-Diaz et al., 2019; Lavraud et al., 2020)

    • 日球层等离子体片的主要观测特征包括:质子数密度增大、磁场极性翻转、超热电子的投掷角发生~180°跃变. 除此之外,还有增强的等离子体βWinterhalter et al., 1994)、阿尔法粒子丰度(Nα/Np)减小(Borrini et al., 1981; Geiss et al., 1995; Bavassano et al., 1997; Suess et al., 2009)、氧离子丰度下降(Suess et al., 2009; Liu et al., 2010)等特征. 日球层等离子体片相对于日球层电流片的位置可能出现的情形:日球层等离子体片可能包围、领先或落后于日球层电流片(Liu et al., 2014). 这些基本特征本质上取决于日球层等离子体片的成因、径向传播演化以及卫星穿越等离子片的位置等因素. 此外,日球层等离子体片内可能存在局地电流片、等离子体波动和磁岛等(Smith and Zhou, 2007).

      日球层等离子体片的厚度(空间尺度)通常是日球层电流片厚度(几个离子回旋半径)的一个量级以上. 地球轨道附近卫星穿越日球层等离子体片的研究结果显示,日球层等离子体片厚度的比较范围比较大,平均厚度大约0.4×106~9.0×106 km(Winterhalter et al., 1994; Lepping et al., 1996; Smith and Zhou, 2007; Simunac et al., 2012). Winterhalter等(1994)发现日球层等离子体片厚度随质子数密度的增大而呈指数形式增大.

      Wu等(2019)进一步统计分析了日球层等离子体片的厚度,发现其厚度存在显著的太阳活动依赖性. 具体而言,日球层等离子体片厚度的对数与太阳黑子数呈良好的线性负相关关系(r = −0.78). 也就是说,日球层等离子体片厚度在太阳活动低年较厚,在太阳活动高年较薄. 这表明日球层等离子体片受到太阳源区的控制和影响,比如磁压力. Winterhalter等(1994)提出日球层等离子体片是一个压力平衡结构,随着太阳风向外对流. 在此基础上,Wu等(2016)进一步提出对流结构受到太阳磁活动的控制,若极区磁场越强,则指向磁赤道的磁压就越大,日球层等离子体片就会变窄;反之日球层等离子体片变厚. 厚度的变化特征似乎支持冕流在行星际空间延伸形成日球层等离子体片的观点;但难以通过交换磁重联不连续地释放等离子体团以及磁场重联产生小等离子体团的物理图像来进行解释. 这充分说明日球层等离子体片的形成机制复杂多样,尚未厘清明晰.

    • 日球层等离子体片的一个典型特征是等离子体密度增强. 地球轨道附近的观测结果表明,绝大多数日球层等离子体片内离子数密度的峰值约30 cm−3,大概是背景太阳风离子数密度的3~4倍(Liou and Wu, 2020). 某些极端情况下,比如2011年9月9日WIND飞船穿越一个日球层等离子体片,观测到离子数密度高达94 cm−3,大概是背景太阳风离子数密度的5倍(Wu et al., 2017). 可见,日球层等离子体片通常是一个具有强动压或动压脉冲的太阳风结构.

      行星在黄道面上运行速度大约每秒几千米至几十千米,比如在地心太阳磁层(GSM)坐标下,水星平均轨道速度约48 km/s、金星平均轨道速度约35 km/s、地球平均轨道速度约30 km/s、火星平均轨道速度约24 km/s,它们穿越日球层等离子体片的时长约数小时至数天,意味着它们将长时间处于强太阳风动压(甚至极端太阳风动压)的条件下. 因此,当日球层等离子体片扫过行星(比如地球)时,磁层的向阳侧会被压缩,垂直磁场方向的粒子数密度和温度会升高(见图6),造成离子温度和电子温度的各向异性,可能激发等离子体波动,比如电磁离子回旋波、合声电子回旋波;与此同时,压缩效应会导致相对论电子快速向向阳侧漂移(梯度漂移),与等离子体波动相遇发生波粒相互作用,粒子通过投掷角散射沉降入低层大气,进而影响行星大气环境(Tsurutani et al., 2016). 下面通过一个观测实例来简述日球层等离子体片的行星空间天气效应.

      图  6  日球层等离子体片扫过地球时,动压脉冲压缩磁层的向阳侧. 圆点表征电子(蓝色)和质子(黑色). 由于日球层等离子体片压缩磁层,垂直磁场方向的粒子数密度和温度会增大(修改自Tsurutani et al., 2016

      Figure 6.  A schematic of a solar wind pressure pulse compressing the outer portion of the dayside magnetosphere. The dots represent electrons (blue) and protons (black). The particle densities and the temperatures perpendicular to the magnetic field are enhanced by the magnetospheric compression due to the solar wind HPS impingement (modified from Tsurutani et al., 2016)

      2015年3月8日至9日,火星探测器MAVEN在火星轨道附近穿越一个日球层等离子体片,观测到等离子体片内离子数密度显著增强,其峰值约15 cm−3,是MAVEN任务期间探测到的最大密度值,大概是背景太阳风离子数密度的4倍以上. Zhao等(2021)详细分析了这个日球层等离子体片事件. 图7显示了2015年3月7日至11日期间MAVEN观测的等离子体和磁场数据. 图中只显示位于火星弓激波上游的数据点,每次弓激波穿越都通过主要特征包括离子能谱增加、太阳风方向和速度突变、离子密度急剧增加、磁场强度突然增加进行了识别. 3月8日至10日期间有一个日冕物质抛射事件,其主要特征包括:增强的磁场强度、下降的质子速度、低等离子体β、低太阳风质子温度、高能离子事件,以及一个前向快激波. 这个激波由此日冕物质抛射驱动,通过高能离子通量的峰值可识别其出现在3月8日15点22分(世界时). 这个日球层等离子体片(阴影区域)嵌入在激波与日冕物质抛射前边界之间的鞘区中,通过质子密度增强和磁场强度下降识别(Winterhalter et al., 1994). 随着日球层等离子体片前边界到达,离子数密度迅速增大,在其中间位置到达峰值. 考虑到卫星轨道的有限空间采样,其实际最大值很可能超过15 cm−3. 密度显著增强可归因于两个因素:日球层等离子体片内离子密度增强特性和激波压缩效应. 而且,鞘区的传播速度也非常之快(~ 820 km/s),使得动压高达 ~18 nPa,是MAVEN任务期间探测到的最大动压值. Jakosky等(2015)详细分析了这个事件的火星空间天气效应,主要包括:弥散极光的形成、拾起离子显著增强、离子逃逸率增大.

      图  7  MAVEN在2015年3月7日至11日期间观测到的一个日球层等离子体片嵌入在行星际日冕物质抛射的鞘区中. 从上至下:MAVEN探测器高度,行星际磁场强度,MSO坐标下的磁场方向仰角和方位角,太阳风速度,密度,温度和由观测速度计算得到的预期温度(红色曲线),质子β,离子能谱,电子能谱,电子投掷角分布(~282 eV),太阳高能离子和电子能谱. 两条垂直的红色虚线表征行星际日冕物质抛射的边界,垂直的黑色虚线表征由行星际日冕物质抛射驱动的激波. 阴影区域表征日球层等离子体片(修改自Zhao et al., 2021

      Figure 7.  MAVEN observations of an HPS embedded within the sheath region of an interplanetary coronal mass ejection (ICME) during 2015 March 07-11. From top to bottom: the MAVEN spacecraft altitude, interplanetary magnetic field strength, elevation angle and azimuthal angle of magnetic field direction in MSO coordinates, solar wind velocity, density, SWIA temperature overlaid with the expected temperature (red dotted curve) from the observed velocity, proton β, ion energy spectra, electron energy spectra, pitch angle (PA) distributions of electron (~282 eV), SEP ion and electron differential flux spectra. Two vertical red dashed lines bound an ICME and the vertical black dashed line mark a shock driven by the ICME. The shaded region indicates the HPS interval (modified from Zhao et al., 2021)

    • 本文简述和讨论了有关日球层等离子体片的一些研究进展,主要关注日球层等离子体片的源区、成因、观测特征和行星空间天气效应. 现有观点普遍认为日球层等离子体片的源区位于盔冕流顶部区域或盔冕流核心区的顶部. 形成机制复杂多样,比如:冕流“茎梗”在行星际空间延伸形成日球层等离子体片,通过磁场重联释放等离子体团形成日球层等离子体片;通过剪切流机制形成位于日球层电流片两侧的日球层等离子体片. 日球层等离子体片的就地观测特征取决于日球层等离子体片的成因、径向传播演化以及卫星穿越等离子片的位置等因素. 离子密度增强的特征意味着日球层等离子体片是一个强动压或动压脉冲的太阳风结构,当它们扫过行星时,行星磁层或诱发磁层的向阳侧会被压缩,导致等离子波的激发以及波粒相互作用的发生等,进而导致拾起离子显著增强,离子逃逸率增大等效应.

      有几个值得进一步探讨的问题:(1)关于日球层等离子体片的成因,哪种形成机制占主动地位?是否还存在其它形成机制,比如包含磁流体波动的机制?(2)如何解释日球层等离子体片的厚度等特征参数随太阳活动的变化,其主要控制因素有哪些?(3)日球层等离子体片内的局地电流片、等离子体波动、磁岛等是如何激发或产生的?(4)日球层等离子体片的行星空间天气效应的一般规律和特征?日球层等离子体片被激波或太阳高速流—低速流相互作用区压缩,会导致哪些极端行星空间天气事件?

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