Turbulence Characteristics of Switchback and Nonswitchback Intervals Observed by Parker Solar Probe
Turbulence Characteristics of Switchback and Nonswitchback Intervals Observed by Parker Solar Probe
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DOI：
10.3847/2041-8213/abbd4a
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发表时间：
2020-12-01
影响因子：
7.9
通讯作者：
Raouafi, Nour E.
中科院分区：
文献类型：
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作者：
Bourouaine, Sofiane;Perez, Jean C.;Raouafi, Nour E.
利用帕克太阳探测器（PSP）在35.7 R ~ 41.7 R的径向距离上对第一次太阳相遇期间的太阳风湍流特征进行了分析。在我们的分析中，我们从非之字形（NSB）间隔中分离出所谓的之字形（SB）间隔（折叠磁场线），NSB间隔主要遵循帕克螺旋场。使用一种基于条件相关函数的技术，我们分别估计了SB和NSB间隔中的Elsasser、磁场和体积速度场的功率谱。通过比较两种区间的湍流能谱，发现了以下特点：（1）后向传播Elsasser场z（-）的去相关长度在NSB区间比在SB区间大;（2）SB层段的磁功率谱比NSB层段陡，谱指数接近-5/3，其具有接近-3/2的光谱指数;（3）SB和NSB湍流都是不平衡的，NSB具有最大的交叉螺旋度;（4）SB间隔中的剩余能量大于NSB，（5）所分析的波动主要由Alfvenic波动控制，对于SB（NSB）湍流，Alfvenic波动沿向阳（反向阳）方向传播。这些观察到的特征提供了进一步的证据，证明PSP观察到的之字形与折叠磁场线有关，从而深入了解其湍流性质。
We use Parker Solar Probe (PSP) in situ measurements to analyze the characteristics of solar wind turbulence during the first solar encounter covering radial distances between 35.7R and 41.7R. In our analysis we isolate so-called switchback (SB) intervals (folded magnetic field lines) from nonswitchback (NSB) intervals, which mainly follow the Parker spiral field. Using a technique based on conditioned correlation functions, we estimate the power spectra of Elsasser, magnetic, and bulk velocity fields separately in the SB and NSB intervals. In comparing the turbulent energy spectra of the two types of intervals, we find the following characteristics: (1) The decorrelation length of the backward-propagating Elsasser field z(-) is larger in the NSB intervals than the one in the SB intervals; (2) the magnetic power spectrum in SB intervals is steeper, with spectral index close to -5/3, than in NSB intervals, which have a spectral index close to -3/2; (3) both SB and NSB turbulence are imbalanced with NSB having the largest cross-helicity, (4) the residual energy is larger in the SB intervals than in NSB, and (5) the analyzed fluctuations are dominated by Alfvenic fluctuations that are propagating in the sunward (antisunward) direction for the SB (NSB) turbulence. These observed features provide further evidence that the switchbacks observed by PSP are associated with folded magnetic field lines giving insight into their turbulence nature.