Flapping of Multifold Heliospheric Current Sheet Observed by Parker Solar Probe

Observations of magnetotail current sheets on many planets, including Earth, Mercury, Venus, and Mars, show widely-existed flapping motion. As the most extensive current sheet in the heliosphere, however, there is no detailed conclusion about whether and how the heliospheric current sheet (HCS) flaps. Parker Solar Probe traversed HCS for five times serially near the perihelion of encounter 7. Based on MVA method and discontinuity type analysis, we find that HCS is multifold on a small scale, and at the same time, flapping upward and downward. The flapping speed is on the order of tens to hundreds km/s. Assuming that the velocity of solar wind is uniform over the same sphere, we construct a three-dimensional image of HCS, which illustrates what the flapping multifold HCS looks like. Our study shows that the heliospheric current sheet is neither flat nor static. Instead, multi-folding and flapping exist at the same time, and it's more complex than commonly thought. The dynamics at the source region of the multifold HCS in the solar atmosphere is also investigated, and its relation with the dynamics in the interplanetary space is discussed as well. This will lead us a deeper understanding of the 3D structure and motion of HCS.