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Macro Magnetic Holes Caused by Ripples in Heliospheric Current Sheet from Coordinated Imaging and Parker Solar Probe Observations

Macro magnetic holes (MMHs), which are significant magnetic field decreases in the solar wind lasting tens of minutes, were found during the first four orbits of the Parker Solar Probe (PSP). We performed a detailed analysis of the 2020 January 30 event and found the possible cause of the MMH using coordinated remote sensing observations from STEREO A and PSP in situ measurements. The results indicate that an MMH represents a brief encounter with the rippled heliospheric current sheet (HCS). Out of the data from the first four orbits of PSP, we identified 17 MMHs and carried out a statistical analysis. Basic characteristics of MMHs include (1) MMHs usually last tens of minutes; (2) the magnetic field strength inside the events is much lower than that in the ambient solar wind; (3) enhanced plasma density, radial velocity, and plasma β are usually found inside the MMHs; and (4) the radial magnetic field has the same polarity before and after an MMH. Based on potential field-source surface and magnetohydrodynamics models, for each of the events we roughly estimate the radial size and the lower limit of the vertical size (i.e., the separation distance between PSP and the HCS), which are 2 R ⊙ and 10 R ⊙ on average, respectively. These results suggest that MMHs are a frequent phenomenon that may shed light on the dynamics of the HCS and the origins and evolutions of the solar wind structures in the heliosphere.