Number density structures in the inner heliosphere
Number density structures in the inner heliosphere
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DOI：
10.1051/0004-6361/201732567
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发表时间：
2018-03
期刊：
影响因子：
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通讯作者：
D. Stansby;T. Horbury
中科院分区：
文献类型：
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作者：
D. Stansby;T. Horbury
慢太阳风的起源和产生机制仍然不清楚。部分缓慢的太阳风被“数密度结构”占据，这些结构是数密度增加的离散斑块，它们被冻结在大块太阳风中并随其移动。在本文中，我们的目的是提供第一个在现场的统计研究在内日球层的数密度结构。我们重新处理了由Helios在内日球层测量的原位离子分布函数，为整个使命提供了一套新的可靠的质子等离子体矩。从这个新的数据集中，我们寻找在太阳0.5 Au范围内测量的数密度结构，并研究它们的性质。我们确定了140个离散区域的数量密度增强。这些结构只发生在缓慢的太阳风中，跨越了从50毫米到2000毫米的广泛长度尺度，其中包括比以前观察到的更小的尺度。它们也始终比周围的等离子体密度更大，温度更高，但磁场强度较低，因此保持压力平衡。我们的观测结果表明，这些结构存在于慢太阳风中，尺度范围很广，其中一些太小，无法被遥感仪器探测到。这些结构是罕见的，仅占Helios测量的慢太阳风的1%，并且对太阳风的质量通量没有显著贡献。
The origins and generation mechanisms of the slow solar wind are still unclear. Part of the slow solar wind is populated by "number density structures", discrete patches of increased number density that are frozen in to and move with the bulk solar wind. In this paper we aimed to provide the first in-situ statistical study of number density structures in the inner heliosphere. We reprocessed in-situ ion distribution functions measured by Helios in the inner heliosphere to provide a new reliable set of proton plasma moments for the entire mission. From this new data set we looked for number density structures measured within 0.5 AU of the Sun and studied their properties. We identified 140 discrete areas of enhanced number density. The structures occurred exclusively in the slow solar wind and spanned a wide range of length scales from 50 Mm to 2000 Mm, which includes smaller scales than have been previously observed. They were also consistently denser and hotter that the surrounding plasma, but had lower magnetic field strengths, and therefore remained in pressure balance. Our observations show that these structures are present in the slow solar wind at a wide range of scales, some of which are too small to be detected by remote sensing instruments. These structures are rare, accounting for only 1\% of the slow solar wind measured by Helios, and are not a significant contribution to the mass flux of the solar wind.