帕克太阳探测器观测到的压缩阿尔夫峰的可能产生机制
Possible Generation Mechanism for Compressional Alfvénic Spikes as Observed by Parker Solar Probe
摘要：
帕克太阳探测器（PSP）发现太阳风中有大量的阿尔夫文速度尖峰和磁场扭结。温度升高是与Alfvénic尖峰相关的另一个显著特征。这些重合现象的原型是如何在源区间歇性地产生的，成为人们广泛关注的热点问题。本文提出了一个新的模型，在不同磁螺旋度的开漏斗和闭环之间的交换磁重联中引入导场不连续性。改进的交换重联模型不仅可以加速新打开的闭合回路中的喷流，而且可以沿着新重联和重联后的开放通量管激发和发射Alfvénic波脉冲。结果表明：（1）Alfvén扰动在时间上具有脉冲性，在空间上具有非对称性;（2）Alfvénic脉冲具有可压缩性，且具有温度增强和密度变化的特征。我们指出，与阿尔文波传播同时发生的三个物理过程可能是导致温度增强的原因：（a）加热射流等离子体的对流（密度降低），（b）压缩慢模波的传播（密度增加），以及（c）热通量的传导（密度的微弱变化）。我们还建议，阿尔夫文脉冲的径向非线性演化应考虑到解释磁之字形的形成。
英文摘要：
The solar wind is found by Parker Solar Probe (PSP) to be abundant with Alfvénic velocity spikes and magnetic field kinks. Temperature enhancement is another remarkable feature associated with the Alfvénic spikes. How the prototype of these coincident phenomena is generated intermittently in the source region becomes a hot topic of wide concerns. Here we propose a new model introducing guide-field discontinuity into the interchange magnetic reconnection between open funnels and closed loops with different magnetic helicities. The modified interchange reconnection model not only can accelerate jet flows from the newly opening closed loop but also excite and launch Alfvénic wave pulses along the newly-reconnected and post-reconnected open flux tubes. We find that the modeling results can reproduce the following observational features: (1) Alfvén disturbance is pulsive in time and asymmetric in space; (2) Alfvénic pulse is compressible with temperature enhancement and density variation inside the pulse. We point out that three physical processes co-happening with Alfvén wave propagation can be responsible for the temperature enhancement: (a) convection of heated jet flow plasmas (decrease in density), (b) propagation of compressed slow-mode waves (increase in density), and (c) conduction of heat flux (weak change in density). We also suggest that the radial nonlinear evolution of the Alfvénic pulses should be taken into account to explain the formation of magnetic switchback geometry.
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