The Near-Sun Streamer Belt Solar Wind: Turbulence and Solar Wind Acceleration
The Near-Sun Streamer Belt Solar Wind: Turbulence and Solar Wind Acceleration
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DOI：
10.1051/0004-6361/202039872
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发表时间：
2021-01
影响因子：
6.5
通讯作者：
C. H. Chen;B. Chandran;Lloyd D. Woodham;S. Jones;J. Perez;S. Bourouaine;T. Bowen;K. Klein;M. Moncuquet;J. Kasper;S. Bale
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文献类型：
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作者：
C. H. Chen;B. Chandran;Lloyd D. Woodham;S. Jones;J. Perez;S. Bourouaine;T. Bowen;K. Klein;M. Moncuquet;J. Kasper;S. Bale
帕克太阳探测器(PSP)的第四个轨道达到了日心距离，低至27.9Rs，使得太阳风湍流和加速机制能够比以前更接近太阳的地方进行现场研究。在PSP第四次太阳相遇的入站和出站部分，湍流特性被发现有很大的不同，这可能是由于出站期间靠近日球层电流片(HCS)。在HCS附近，在流光带风中，湍流具有较低的振幅，较高的磁可压缩性，较陡峭的磁场谱(谱指数接近-5/3而不是-3/2)，较低的Alfvenity，以及在低得多的频率下的“1/f”突变。这些也是1au的慢风的特征，表明近太阳流光带风是典型的慢太阳风。性质上的转变发生在距离HCS约4度的预计角距离处，这意味着在这些距离处流光带风的全宽度约为8度。虽然PSP测量的大部分Alfvenic湍流能量通量与太阳风加速的反射驱动湍流模式所需的能量通量一致，但流光带的能量通量明显低于模式预测，这表明需要额外的机制来解释流光带太阳风的加速。
The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances down to 27.9 Rs, allowing solar wind turbulence and acceleration mechanisms to be studied in situ closer to the Sun than previously possible. The turbulence properties were found to be significantly different in the inbound and outbound portions of PSP's fourth solar encounter, likely due to the proximity to the heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the streamer belt wind, the turbulence was found to have lower amplitudes, higher magnetic compressibility, a steeper magnetic field spectrum (with spectral index close to -5/3 rather than -3/2), a lower Alfvenicity, and a "1/f" break at much lower frequencies. These are also features of slow wind at 1 au, suggesting the near-Sun streamer belt wind to be the prototypical slow solar wind. The transition in properties occurs at a predicted angular distance of ~4 degrees from the HCS, suggesting ~8 degrees as the full-width of the streamer belt wind at these distances. While the majority of the Alfvenic turbulence energy fluxes measured by PSP are consistent with those required for reflection-driven turbulence models of solar wind acceleration, the fluxes in the streamer belt are significantly lower than the model predictions, suggesting that additional mechanisms are necessary to explain the acceleration of the streamer belt solar wind.