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Electrodynamic coupling in the solar wind-magnetosphere-ionosphere system

期刊名称：Chinese Journal of Space Science
时间：0
页码：321-332
分类：P353[天文地球—空间物理学;天文地球—地球物理学]
作者机构：[1]中国科学技术大学地球与空间科学学院中科院基础等离子体物理重点实验室,合肥230026, [2]中国科学院空间科学与应用研究中心空间天气学国家重点实验室,北京100080
相关基金：国家自然科学基金（40831060,40621003）和国家科技部973项目（G2006CB806304）资助.
相关项目：空间天气基本物理过程和集成预报模式研究

作者： HU Youqiu|HU Youqiu|Wang Chi|Wang Chi|

关键词：地球磁层, 行星际磁场, 弓激波, Earth＇s magnetosphere, Interplanetary magnetic field, Bow shock

中文摘要：

通过对太阳风-磁层-电离层系统的全球MHD模拟,研究地球弓激波相对日地连线的旋转非对称性.模拟限于太阳风速度沿日地连线、地球磁偶极矩和行星际磁场（IMF）与日地连线垂直的简单情况.模拟结果表明,即便对于IMF强度为零的情况,弓激波相对目地连线也不具备旋转对称性质：终端面（晨昏子午面）及其向阳侧的弓激波截线的东西宽度大于南北宽度（约9%～11%）,终端面尾侧的弓激波截线东西宽度小于南北宽度（约8%）.在存在IMF的情况下,弓激波的位形同时受到磁层顶的形状和快磁声波速度各向异性的影响.磁层顶向外扩张并沿IMF方向拉伸,且其扩张和拉伸程度随IMF由北转南而增强.在磁鞘中,垂直于磁场方向的快磁声波速度高于平行方向.因此,磁层顶拉伸方向与快磁声波速度最大方向垂直,它们对弓激波位置的效应恰好相反;弓激波的最终形状取决于何种效应占据主导地位.对于终端面尾侧,快磁声波速度的各向异性起主导作用,弓激波截线沿IMF垂直方向的宽度大于平行方向.对于终端面及其向阳侧,弓激波截线的形状与IMF取向有关：在准北向或晨昏向IMF情况下,弓激波截线沿IMF垂直方向的宽度仍大于平行方向;在准南向IMF情况下,弓激波截线沿IMF垂直方向的宽度小于平行方向的.鉴于弓激波形状同IMF取向之间的密切关系,我们提议以IMF为基准方向,提取弓激波截线的平行半宽度Rb//和垂直半宽度Rb⊥作为尺度参数.这些尺度参数和通常引入的弓激波截线的东西半宽度yb和南北半宽度zb相比,更为合理地表征了弓激波的几何性质.模拟结果表明,在终端面上,yb/zb和Rb///Rb⊥在IMF各向同性取向下的统计平均值均低于1,与观测得到的结论一致.

英文摘要：

In terms of global magnetohydrodynamic （MHD） simulations of the solar wind-magnetosphere-ionosphere system, this paper investigates the rotational asymmetry of the Earth′s bow shock with respect to the Sun-Earth line. We are limited to simple cases in which the solar wind is along the Sun-Earth Line, and both the Earth′s magnetic dipole moment and the interplanetary magnetic field （IMF） are perpendicular to the Sun-Earth line. It is shown that even for the case of vanishing IMF strength the bow shock is not rotationally symmetric with respect to the Sun-Earth line： the east-west dimension of the cross section of the bow shock exceeds the north-south dimension by about 9~11% on the terminator plane （dawn-dusk meridian plane） and its sunward side, and becomes smaller than the north-south dimension by about 8% on the tailward side of the terminator plane. In the presence of the IMF, the configuration of the bow shock is affected by both the shape of the magnetopause and the anisotropy of the fast magnetosonic wave speed. The magnetopause expands outward, being stretched along the IMF, and the extent of its expansion and stretch increases when the IMF rotates from north to south. In the magnetosheath, the fast magnetosonic wave speed is higher in the direction perpendicular to the magnetic field than that in the parallel direction. Therefore, the stretch direction of the magnetopause is perpendicular to the maximum direction of the fast magnetosonic wave speed, and their effects on the bow shock position are exactly opposite. The eventual shape of the bow shock depends on which effect dominates. On the tailward side of the terminator plane, the anisotropy of the fast magnetosonic wave speed dominates, so the cross section of the bow shock is wider in the direction perpendicular to the IMF. On the terminator plane and its sunward side, the shape of the bow shock cross section depends on the orientation of the IMF： the bow shock cross section is still wider in the direction perpendicular to the I

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