Categorizing MHD Discontinuities in the Inner Heliosphere by Utilizing the PSP Mission

Abstract

AbstractThe 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 . 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.