Latitudinal dependence of the radial IMF component: Coronal imprint
Latitudinal dependence of the radial IMF component: Coronal imprint
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径向 IMF 分量的纬度依赖性：冠状印记
DOI：
10.1029/96gl02908
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发表时间：
1996
影响因子：
5.2
通讯作者：
E. Smith
中科院分区：
文献类型：
--
作者：
S. Suess;E. Smith
抽象的。尤利西斯号的测量证实，行星际磁场的径向分量 Br 相对于日磁纬度不存在明显的梯度。在日冕中，等离子体/3 << l，除了直接在流光上方之外，因此当太阳风将磁通量带离太阳时，场强的纵向和横向梯度将由于横向磁压力梯度力而松弛。这种情况发生得足够快，以至于场基本上均匀了 5-10 Re，显然在超过 1 AU 时仍然如此。在这里，我们通过定性物理论证并参考详细的 MHD 模拟来说明冠状弛豫。 1. 1993-1995 年《尤利西斯》简介 [Smith 和 Balogh，1995； Baloghet al., 1995] 以及 ICE 和 IMP-8 在 1984-1988 年 [Burtonet al., 1995] 在日心距离为 1-4 AU 的行星际磁场 (IMF) 的径向分量 Br 中观察到日磁纬度没有显着梯度。这些观测是在太阳极小值附近进行的，此时太阳的磁场最接近轴向排列的偶极子。图 1 显示了 IMP-8 和 ICE 的结果，缩放至 1 AU，并根据磁纬度绘制。数据是五个度的平均值。曲线 (a)、(b) 和 (c) 来自模型，这将在下面讨论。磁赤道附近 Br 中明显的小梯度可能是由于扇区识别中的小错误造成的，因此真实梯度完全可以忽略不计。 Ulysses 在 1993-1995 年观测到日照纬度 80° 基本上没有梯度。这里我们讨论日冕顶部磁场的原因，即：在 10 Ro 处，在日光层等离子体片 (HPS) 之外没有任何显着的梯度纬度或经度 [Gosling et al., 1981] 围绕日光层电流片 (HCS)。在§2中，我们解释了原因
Abstract. Measurements by Ulysses have confirmedthat there is no significant gradient with respect to he-liomagnetic latitude in the radial component, Br, of theinterplanetary magnetic field. In the corona, the plasma/3 is << l, except directly above streamers, so longitudi-nal and latitudinal gradients in field strength will relaxdue to the transverse magnetic pressure gradient forceas the solar wind carries magnetic flux away from theSun. This happens quickly enough so that the field isessentially uniform by 5- 10 Re, apparently remainingso as it is carried to beyond 1 AU. Here, we illustrate thecoronal relaxation with a qualitative physical argumentand by reference to a detailed MHD simulation. 1. Introduction Ulysses in 1993-1995 [Smith and Balogh, 1995; Baloghet al., 1995] and ICE and IMP-8 in 1984-1988 [Burtonet al., 1995] observed no significant gradient in helio-magnetic latitude in the radial component, Br, of theinterplanetary magnetic field (IMF) at heliocentric dis-tances of 1-4 AU. These observations were made nearsolar minimum when the Sun's magnetic field is mostnearly an axially aligned dipole. Figure 1 shows theresults from IMP-8 and ICE scaled to 1 AU and plot-ted against magnetic latitude. The data are five degreebin averages. Curves (a), (b), and (c) are from mod-els which will be discussed below. The apparent smallgradient in Br near the magnetic equator is probablydue to small errors in sector identification so that thetrue gradient is completely negligible. Essentially nogradient was observed by Ulysses in 1993-1995 up to aheliographic latitude of 80 °. Here we discuss the rea-son why the magnetic field at the top of the corona,i.e. at 10 Ro, does not have any significant gradient inlatitude or longitude outside of the heliospheric plasmasheet (HPS) [Gosling et al., 1981] surrounding the he-liospheric current sheet (HCS). In §2, we explain why