Categorizing MHD Discontinuities in the Inner Heliosphere by Utilizing the PSP Mission. Issue 3 (26th February 2022)

• Record Type: Journal Article
• Authors: Liu, Y. Y.; Fu, H. S.; Cao, J. B.; Yu, Y.; Liu, C. M.; Wang, Z.; Guo, Z. Z.; He, R. J.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-26
• Subjects: Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2021JA029983
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: The interplanetary discontinuities (IDs) have been widely observed in astrophysical and space plasmas, while their characteristics and evolutions within 0.3 AU are still unclear due to the limitation of spacecraft orbits in previous missions. Here, we report three ID events, including a rotational discontinuity (RD), a tangential discontinuity (TD), and a suspected contact discontinuity (CD), detected by the Parker Solar Probe in a previously unexplored region of the heliosphere as close to the Sun as 0.13 AU. By the combination of the minimum variance analysis technique, the Walén relation and the continuity condition of the electric field, the ID orientations, propagations, and thicknesses are determined, showing a smaller typical ID thickness on the order of 100 km therein. Automated event selection using a magnetic field change threshold criterion is conducted with the PSP field data on Orbits 4 and 5. In total, 3, 948 IDs are collected, yielding a ratio of RD : TD : ED : ND = 73 : 4 : 22 : 1 % $\text{RD}:\text{TD}:\text{ED}:\text{ND}=73:4:22:1\text{\%}$ . The IDs within 0.4 AU account for 87% of the total IDs, resulting in sharp ID occurrence rate decrease with heliocentric distance, from ∼140 days −1 for RDs and ∼8 days −1 for TDs at 0.13 AU to about 1 day −1 for both RDs and TDs at r > 0.6 AU. Within 0.3 AU, the RDs with tiny propagation angles, i.e., the angles between the magnetic fields and the RD normals, predominate in all kinds of IDs. We further analyze the jump conditions of these IDs statistically, and find that the changes in magnetic fields and particle parameters are theoretically consistent. Plain Language Summary: The interplanetary discontinuities are spatial structures characterized by abrupt changes in the vector magnetic field and/or the plasma properties, and have been widely observed in astrophysical and space plasmas. The magnetohydrodynamics theory predicts the existence of four classes of discontinuities in the magnetized plasmas, i.e., the shocks and rotational/tangential/contact discontinuities (RDs/TDs/CDs). Previous studies of the characteristics/evolutions of the interplanetary discontinuities cover the heliocentric distances from 0.3 AU to 19 AU limited by satellites' orbits, while their characteristics/evolutions within 0.3 AU are still unclear. In this study, we report three discontinuity events by utilizing the Parker Solar Probe (PSP) measurements in a previously unexplored region of the heliosphere as close to the Sun as 0.13 AU. By a comprehensive analysis method, the discontinuity types, orientations, propagations, and thicknesses are determined. By using the magnetic field jumps as the selection criterion, we scour the 8‐month PSP field data via an automated algorithm and establish an event list which contains 3, 948 discontinuity events. We find that the interplanetary discontinuities are more abundant at smaller heliocentric distances, and the RD predominate, accounting for 73% of the discontinuities in space. These results are useful for further statistical investigation of the characteristics/evolutions of the near‐Sun IDs. Key Points: Three rotational/tangential/contact discontinuities as close to the Sun as 0.13 AU are investigated The discontinuity motions/thicknesses are determined by combining the Walén relation and the continuity condition of the electric field The ID occurrence rate decreases more dramatically with heliocentric distance within 0.3 AU