Flapping of Multifold Heliospheric Current Sheet Observed by Parker Solar Probe

Abstract The heliospheric current sheet (HCS) represents the most expansive current sheet within the heliosphere. However, there has been a lack of specific analysis regarding the potential folding and flapping of the HCS. The Parker Solar Probe (PSP) offers a unique opportunity to investigate this phenomenon because it can traverse the HCS multiple times during its perihelion encounters with the Sun. During the perihelion of Encounter 7, PSP successively crossed the HCS five times. Utilizing the minimum variance analysis method and discontinuity type analysis on the in situ measurements, we observed that the HCS exhibits a multifolded structure at small scales, coupled with an upward and downward flapping motion. The flapping velocities are estimated to range from several to hundreds of kilometers per second. By employing a two-step ballistic backmapping of the magnetic field in conjunction with observations from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory, we deduced that the flapping motion may be instigated by a solar flare eruption at the source region. Furthermore, we confirmed that the multiple folds are not merely localized manifestations of the Kelvin–Helmholtz instability. Our research indicates that the HCS is, in reality, a dynamic 3D structure characterized by a complex small-scale morphology and its movements are intricately linked to the activities in the source region, revealing a level of complexity that surpasses previous understandings.