Alpha–Proton Differential Flow of the Young Solar Wind: Parker Solar Probe Observations
Alpha–Proton Differential Flow of the Young Solar Wind: Parker Solar Probe Observations
复制标题
年轻太阳风的阿尔法-质子差流：帕克太阳探测器观测
DOI：
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发表时间：
2022
影响因子：
7.9
通讯作者：
S. Bale
中科院分区：
文献类型：
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作者：
P. Mostafavi;R. Allen;M. McManus;G. Ho;N. Raouafi;D. Larson;J. Kasper;S. Bale
α粒子相对于质子的速度可以根据太阳风的类型和与太阳的距离而变化。从以前的航天器的测量提供了α-质子差速度下降到0.3 Au。帕克太阳探测器（PSP）现在首次能够深入了解新加速的太阳风靠近太阳的差异流动。在这里，我们研究的PSP近日点附近的遇到3-7时，核心太阳风的太阳探测器分析仪离子仪器的视野中的质子和α体速度之间的差异。正如以前在较大的日光层距离报告，α质子差速度观测PSP是更大的快风比慢太阳风。我们比较PSP观测与各种航天器的测量，并提出了径向和时间演化的α-质子差速度。差异流随着太阳风从太阳传播而减小，与以前的观测结果一致。虽然太阳神显示了一个小的径向依赖性的差异流的缓慢的太阳风，PSP清楚地显示了这种依赖性的年轻缓慢的太阳风下降到0.09 Au。我们的分析表明，α-质子差速度的大小主要是低于本地阿尔文速度。此外，阿尔法粒子通常比靠近太阳的质子移动得更快。PSP在第八次相遇时穿过阿尔芬表面，并可能在未来的相遇中穿过它，使我们能够首次调查非常接近太阳风加速源区的差异流。
The velocity of alpha particles relative to protons can vary depending on the solar wind type and distance from the Sun. Measurements from the previous spacecraft provided the alpha–proton differential velocities down to 0.3 au. The Parker Solar Probe (PSP) now enables insights into differential flows of the newly accelerated solar wind closer to the Sun for the first time. Here we study the difference between proton and alpha bulk velocities near PSP perihelia of encounters 3–7 when the core solar wind is in the field of view of the Solar Probe Analyzer for Ions instrument. As previously reported at larger heliospheric distances, the alpha–proton differential speed observed by PSP is greater for fast wind than the slow solar wind. We compare PSP observations with various spacecraft measurements and present the radial and temporal evolution of the alpha–proton differential speed. The differential flow decreases as the solar wind propagates from the Sun, consistent with previous observations. While Helios showed a small radial dependence of differential flow for the slow solar wind, PSP clearly showed this dependency for the young slow solar wind down to 0.09 au. Our analysis shows that the alpha–proton differential speed’s magnitude is mainly below the local Alfvén speed. Moreover, alpha particles usually move faster than protons close to the Sun. The PSP crossed the Alfvén surface during its eighth encounter and may cross it in future encounters, enabling us to investigate the differential flow very close to the solar wind acceleration source region for the first time.