Solar zenith angle-dependent asymmetries in Venusian bow shock location revealed by Venus Express
Solar zenith angle-dependent asymmetries in Venusian bow shock location revealed by Venus Express
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金星快车揭示了金星弓形激波位置中与太阳天顶角相关的不对称性
DOI：
10.1002/2015ja021221
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发表时间：
2015
影响因子：
2.8
通讯作者：
Futaana Yoshifumi
中科院分区：
文献类型：
--
作者：
Chai Lihui;Wan Weixing;Fraenz Markus;Zhang Tielong;Dubinin Eduard;Wei Yong;Li Yi;Rong Zhaojin;Zhong Jun;Han Xiuhong;Futaana Yoshifumi
长期以来，人们都知道金星弓形激波（BS）的位置是不对称的，这是从长期存在的先锋金星轨道器使命的观测结果来看的。金星快车（VEX）使命不仅在终结者区域，而且在近太阳下和尾部区域几乎垂直地穿过BS。利用VEX轨道几何的优势，我们检查了在太阳活动周期23和24之间的长期太阳极小期期间观测到的BS交叉的大型数据集，发现金星BS不对称性表现出太阳天顶角的依赖性。在终结者和尾部区域，在金星BS位置观察到磁极-赤道和南北不对称，这与先驱者金星轨道器（PVO）在终结者附近的观测相似。然而，在近太阳下区域，只观察到磁南北;即，BS形状在磁南极上向内凹进，在磁北极上向外凸出。在近太阳下区域不存在磁极-赤道不对称性表明磁极-赤道不对称性主要是由不对称的波传播而不是离子拾取过程引起的。太阳极小期明显的南北磁不对称性，这是PVO没有观测到的，这表明即使在低持续时间的太阳极小期，离子拾取过程在金星空间环境中也是非常重要的。
It has been long known that the Venusian bow shock (BS) location is asymmetric from the observations of the long‐lived Pioneer Venus Orbiter mission. The Venus Express (VEX) mission crossed BS near perpendicularly not only in the terminator region but also in the near‐subsolar and tail regions. Taking the advantage of VEX orbit geometry, we examined a large data set of BS crossings observed during the long‐lasting solar minimum between solar cycles 23 and 24 and found that the Venusian BS asymmetries exhibit dependence of solar zenith angle. In the terminator and tail regions, both the magnetic pole‐equator and north‐south asymmetries are observed in Venusian BS location, which is similar to the Pioneer Venus Orbiter (PVO) observation near terminator. However, in the near‐subsolar region, only the magnetic north‐south is observed; i.e., the BS shape is indented inward over magnetic south pole and bulged outward over magnetic north pole. The absence of the magnetic pole‐equator asymmetry in the near‐subsolar region suggests that the magnetic pole‐equator asymmetry is mainly caused by the asymmetric wave propagation rather than the ion pickup process. The evident magnetic north‐south asymmetry in solar minimum, which is not observed by PVO, suggests that even during the low long‐lasting solar minimum, the ion pickup process is very important in Venusian space environment.