Self-similar Outflows at the Source of the Fast Solar Wind: A Smoking Gun of Multiscale Impulsive Reconnection?

We present results of a quantitative analysis of structured plasma outflows above a polar coronal hole observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) spacecraft. In a 6 hr interval of continuous high-cadence SDO/AIA images, we identified more than 2300 episodes of small-scale plasma flows in the polar corona. The mean upward flow speed measured by the surfing transform technique is estimated to be 122 ± 34 km s−1, which is comparable to the local sound speed. The typical recurrence period of the flow episodes is 10–30 minutes, and the mean duration and transverse size of each episode are about 3–5 minutes and 3–4 Mm, respectively. The largest identifiable episodes last for tens of minutes and reach widths up to 40 Mm. For the first time, we demonstrate that the polar coronal-hole outflows obey a family of power-law probability distributions characteristic of impulsive interchange magnetic reconnection. Turbulent photospheric driving may play a crucial role in releasing magnetically confined plasma onto open field. The estimated occurrence rate of the detected self-similar coronal outflows is sufficient for them to make a dominant contribution to the fast-wind mass and energy fluxes and to account for the wind’s small-scale structure.

我们展示了对太阳动力学天文台（SDO）航天器上的大气成像组件（AIA）所观测到的极区冕洞上方结构化等离子体外流的定量分析结果。在连续的高帧率SDO/AIA图像的6小时区间内，我们在极区日冕中识别出了2300多次小规模等离子体流事件。通过冲浪变换技术测量的平均向上流速估计为122±34 km s⁻¹，这与当地声速相当。流事件的典型重现周期为10 - 30分钟，每个事件的平均持续时间和横向尺寸分别约为3 - 5分钟和3 - 4兆米。可识别的最大事件持续数十分钟，宽度可达40兆米。我们首次证明极区冕洞外流遵循一系列脉冲式交换磁重联所特有的幂律概率分布。湍动的光球层驱动可能在将受磁场约束的等离子体释放到开放磁场中起着关键作用。所探测到的自相似日冕外流的估计发生率足以使它们对快风的质量和能量通量做出主要贡献，并解释风的小规模结构。