Motion of polar cap arcs
Motion of polar cap arcs
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DOI：
10.1029/2010ja015906
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发表时间：
2011
影响因子：
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通讯作者：
K. Hosokawa;J. Moen;K. Shiokawa;Y. Otsuka
中科院分区：
文献类型：
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作者：
K. Hosokawa;J. Moen;K. Shiokawa;Y. Otsuka
[1]利用加拿大索鲁特湾(74.73°N，265.07°E)全天成像仪5年的光学观测资料，对极帽弧线的运动进行了统计。我们使用自动弧线检测算法识别了743条弧线，并统计检验了它们的移动速度，这是由Hosokawa等人的方法估计的。(2006年)。所研究的弧数大约是Valladares等人以前统计的极帽弧数的5倍。(1994)；因此，我们可以预期获得更具统计学意义的结果。极帽圆弧分为两个不同的类别：辅助依赖和辅助独立的圆弧。前几个弧线的运动遵循Valladares等人报道的规则。(1994)，他展示了稳定的极帽弧向行星际磁场的方向移动。在国际货币基金组织向北移动的条件下，大约三分之二的弧线属于这一类。后一种弧线总是向极地移动，而与IMF by的符号无关，这可能对应于Shiokawa等人报告的晨侧向极地移动的弧线。(1997年)。至少有三分之一的弧线属于这一类别。当IMF by的量级较大时，依赖于By的弧会移动得更快，这表明通过叶重连将开放通量从一个极冠室输送到另一个极冠室控制了它们的运动。相反，非独立圆弧的速度与非独立圆弧的大小无关。辅助依赖和辅助独立弧线的运动很可能是由磁层对流引起的。副依赖弧区的对流受IMF by的影响，这表明它们的来源可能在开放场线上或在与开闭边界相邻的闭合磁层中，而副独立弧似乎很好地位于闭合场线上。因此，两种类型的电弧的磁层源可能是不同的。这意味着，在两种类型的极帽弧中，导致弧形运动和生成的机制可能不同。
[1] A statistics of motion of polar cap arcs is conducted by using 5 years of optical data from an all-sky imager at Resolute Bay, Canada (74.73°N, 265.07°E). We identified 743 arcs by using an automated arc detection algorithm and statistically examined their moving velocities as estimated by the method of Hosokawa et al. (2006). The number of the arcs studied is about 5 times larger than that in the previous statistics of polar cap arcs by Valladares et al. (1994); thus, we could expect to obtain more statistically significant results. Polar cap arcs are found to fall into two distinct categories: the By-dependent and By-independent arcs. The motion of the former arcs follows the rule reported by Valladares et al. (1994), who showed that stable polar cap arcs move in the direction of the interplanetary magnetic field (IMF) By. About two thirds of the arcs during northward IMF conditions belong to this category. The latter arcs always move poleward irrespective of the sign of the IMF By, which possibly correspond to the poleward moving arcs in the morning side reported by Shiokawa et al. (1997). At least one third of the arcs belong to this category. The By-dependent arcs tend to move faster when the magnitude of the IMF By is larger, suggesting that the transport of open flux by lobe reconnection from one polar cap compartment to the other controls their motion. In contrast, the speed of the By-independent arcs does not correlate with the magnitude of the By. The motions of both the By-dependent and By-independent arcs are most probably caused by the magnetospheric convection. Convection in the region of By-dependent arcs is affected by the IMF By, which indicates that their sources may be on open field lines or in the closed magnetosphere adjacent to the open-closed boundary, whereas By-independent arcs seem to be well on closed field lines. Hence, the magnetospheric source of the two types of arc may be different. This implies that the mechanisms causing the motion and generation of arcs could be different between the two types of polar cap arc.