Solar Orbiter observations of the Kelvin-Helmholtz waves in the solar wind
Solar Orbiter observations of the Kelvin-Helmholtz waves in the solar wind
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DOI：
10.1051/0004-6361/202140915
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发表时间：
2021-12-14
影响因子：
6.5
通讯作者：
Angelini, V
中科院分区：
文献类型：
--
作者：
Kieokaew, R.;Lavraud, B.;Angelini, V
上下文。Kelvin-HeImholtz(KH)不稳定性是一种在等离子体中剪切流界面处发展起来的非线性剪切驱动不稳定性。已经在各种天体物理等离子体中推断出KH波，并在太阳系行星的磁层边界和在日冕物质抛射边界的遥感中原位观测到KH波。目标。KH波也有望在太阳风中的气流切变界面上发展。虽然它们被假设在等离子体混合和引发太阳风波动方面发挥重要作用，但它们在太阳风中的直接和明确观测仍然缺乏。方法：研究方法。我们报道了利用太阳轨道器在KH波巡航阶段对其准周期磁场和速度场变化的现场观测。它们被发现在日球层电流片附近的慢太阳风的剪切层中。进行了分析以得出波的局部构型。还建立了具有近似经验值的二维磁流体力学模拟，以检验剪切层的稳定性。此外，对该事件的磁谱进行了分析。结果。我们从线性理论分析中发现，观测条件满足KH不稳定性开始判据，模拟进一步证实了它的发展。目前的薄片几何分析被发现与KH波的发展是一致的，尽管由于事件和太阳风传播的复杂3D性质，可能存在一些限制。此外，我们还报道了在KH波间隔内的压缩电流片上观察到与磁重联一致的离子喷流。结果表明，KH活动激发磁场和速度涨落，在惯性和耗散范围内分别近似遵循k(-5/3)和k(-2.8)的幂定律标度。最后，我们讨论了以往资料中缺乏KH波原位探测的原因。结论。这些观测结果为太阳风中KH波的发展提供了强有力的证据。这为KH波所介导的切变驱动湍流过程提供了新的线索，并对太阳风波动的驱动产生了影响。
Context. The Kelvin-HeImholtz (KH) instability is a nonlinear shear-driven instability that develops at the interface between shear flows in plasmas. KH waves have been inferred in various astrophysical plasmas, and have been observed in situ at the magnetospheric boundaries of solar-system planets and through remote sensing at the boundaries of coronal mass ejections. Aims. KH waves are also expected to develop at flow shear interfaces in the solar wind. While they were hypothesized to play an important role in the mixing of plasmas and in triggering solar wind fluctuations, their direct and unambiguous observation in the solar wind was still lacking. Methods. We report in situ observations of quasi-periodic magnetic and velocity field variations plausibly associated with KH waves using Solar Orbiter during its cruise phase. They are found in a shear layer in the slow solar wind in the close vicinity of the heliospheric current sheet. An analysis was performed to derive the local configuration of the waves. A 2D magnetohydrodynamics simulation was also set up with approximate empirical values to test the stability of the shear layer. In addition, magnetic spectra of the event were analyzed. Results. We find that the observed conditions satisfy the KH instability onset criterion from the linear theory analysis, and its development is further confirmed by the simulation. The current sheet geometry analyses are found to be consistent with KH wave development, albeit with some limitations likely owing to the complex 3D nature of the event and solar wind propagation. Additionally, we report observations of an ion jet consistent with magnetic reconnection at a compressed current sheet within the KH wave interval. The KH activity is found to excite magnetic and velocity fluctuations with power law scalings that approximately follow k(-5/3) and k(-2.8) in the inertial and dissipation ranges, respectively. Finally, we discuss reasons for the lack of in situ KH wave detection in past data. Conclusions. These observations provide robust evidence of KH wave development in the solar wind. This sheds new light on the process of shear-driven turbulence as mediated by the KH waves with implications for the driving of solar wind fluctuations.