[论文解读] A persistent quiet-Sun small-scale tornado III. Waves

Tziotziou, Kostas, Tsiropoula, Georgia+1 more|arXiv (Cornell University)|Oct 13, 2020

Solar and Space Plasma Dynamics被引用 21

一句话总结

本研究利用瑞典太阳望远镜/CRISP获取的高分辨率Hα和Ca ii 8542 Å时间序列，研究了持久日面暗区涡流中的波动力学。识别出向上传播的快磁声波（20–30 km s⁻¹）和局域化的扭转阿尔芬波，且存在驻波模式的证据，可能源于过渡区的波反射，表明涡流流动可作为日冕和色球层能量传输的导管。

ABSTRACT

Vortex flows can foster a variety of wave modes. A recent oscillatory analysis of a persistent 1.7 h vortex flow with a significant substructure has suggested the existence of various types of waves within it. We investigate the nature and characteristics of waves within this quiet-Sun vortex flow to better understand its physics and dynamics. We used a cross-wavelet spectral analysis between pairs of Ha and Ca II 8542 intensity time series at different wavelengths and, hence, atmospheric heights, acquired with CRISP/SST, as well as the derived Ha Doppler velocity and full width at half maximum (FWHM) time series. We constructed halftone frequency-phase difference plots and investigated the existence and propagation characteristics of different wave modes. Our analysis suggests the existence of upwards propagating Alfvenic type waves with phase speeds of ~20-30 km/s. The dominant wave mode seems to be the fast kink wave mode; however, our analysis also suggests the existence of localised Alfvenic torsional waves related to the dynamics of individual chromospheric swirls that characterise the substructure of the vortex flow. The Ha V-I phase difference analysis seems to imply the existence of a standing wave pattern possibly arising from the interference of upwards propagating kink waves with downwards propagating ones that are reflected at the transition region or the corona. Moreover, the results provide further evidence that the central chromospheric swirl drives the dynamics of the vortex flow. This is the first exhaustive phase difference analysis within a vortex flow that explores the nature and dynamics of different wave modes within it. The questions, however, of whether, and how, the dissipation of the derived wave modes occurs and if vortex flows ultimately play a role in the energy budget of the upper layers of the solar atmosphere remain open.

研究动机与目标

• 理解持久日面暗区涡流中波模式的性质与动力学特征。
• 确定波在多个大气层之间的传播特性及相位关系。
• 研究涡流中波模式是否有助于太阳大气中的能量传输与加热。
• 考察单个色球层涡旋在驱动涡流结构内波活动中的作用。

提出的方法

• 在不同大气高度上，对Hα和Ca ii 8542 Å强度时间序列进行交叉波谱谱分析。
• 利用瑞典太阳望远镜CRISP观测数据提取的多普勒速度和FWHM时间序列。
• 构建半色调频率-相位差图以分析波的传播与干涉模式。
• 比较不同大气层之间的相位差，推断波模式类型与传播方向。
• 应用振荡分析技术识别波模式及其在涡流结构中的相干性。
• 评估相位差对过渡区或日冕处波反射及驻波形成的含义。

实验结果

研究问题

• RQ1 在持久日面暗区涡流中存在哪些类型的磁流体力学波模式？
• RQ2 波模式如何在色球层中传播并进入太阳高层大气？
• RQ3 在Hα最小强度区域观测到的驻波模式的成因是什么？
• RQ4 单个色球层涡旋在多大程度上促进了局域化的扭转阿尔芬波活动？
• RQ5 波的反射与干涉模式在波能量传输与耗散中起何种作用？

主要发现

• 快磁声波模式以约20–30 km s⁻¹的相速度向上穿过色球层传播。
• 局域化的扭转阿尔芬波与单个色球层涡旋相关，表明存在局域能量转移。
• 通过Hα V-I相位差分析推断出驻波模式，可能源于向上与向下传播的磁声波之间的干涉。
• 推测过渡区或日冕处的波反射是形成观测到的驻波模式的机制。
• 中心色球层涡旋被确定为涡流流动动力学及伴随波活动的主要驱动源。
• 结果表明，涡流结构可能作为阿尔芬波与磁声波的波导，潜在地促进色球层与日冕加热。