arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2109.06341astro-ph.SRphysics.plasm-phphysics.space-ph
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内日球层之字形的演变

Evolution of switchbacks in the inner Heliosphere

Anna Tenerani, Nikos Sioulas, Lorenzo Matteini, Olga Panasenco, Chen Shi, Marco Velli

摘要:

我们分析了PSP前六次遭遇、三次Helios快流和两次Ulysses南极经过的磁场数据,覆盖了日心距离$0.1\lesssim R\lesssim 3$ au。我们使用这个数据集来统计确定不同周期和幅度的之字形的演变与距离太阳。我们比较的径向演变的磁场方差的均方振幅的之字形,并量化的径向演变的累积计数的之字形每公里。我们发现之字形的振幅下降速度比整体的湍流波动,在某种程度上与径向减少的平均磁场。这可能是振幅饱和的结果,也可能是太阳风中大振幅阿尔夫文波动衰减过程的特征。我们发现,在太阳风中发生之字形的演变是尺度依赖的:随着径向距离的增加,而较短的之字形的持续时间较长的部分减少。这意味着之字形动力学是一个复杂的过程,涉及衰变和在日光层内原位生成。我们确认,之字形可以产生的膨胀,虽然其他类型的之字形产生更接近太阳不能排除。

英文摘要:

We analyze magnetic field data from the first six encounters of PSP, three Helios fast streams and two Ulysses south polar passes covering heliocentric distances $0.1\lesssim R\lesssim 3$ au. We use this data set to statistically determine the evolution of switchbacks of different periods and amplitudes with distance from the Sun. We compare the radial evolution of magnetic field variances with that of the mean square amplitudes of switchbacks, and quantify the radial evolution of the cumulative counts of switchbacks per km. We find that the amplitudes of switchbacks decrease faster than the overall turbulent fluctuations, in a way consistent with the radial decrease of the mean magnetic field. This could be the result of a saturation of amplitudes and may be a signature of decay processes of large amplitude Alfvénic fluctuations in the solar wind. We find that the evolution of switchback occurrence in the solar wind is scale-dependent: the fraction of longer duration switchbacks increases with radial distance whereas it decreases for shorter switchbacks. This implies that switchback dynamics is a complex process involving both decay and in-situ generation in the inner heliosphere. We confirm that switchbacks can be generated by the expansion although other type of switchbacks generated closer to the sun cannot be ruled out.

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