New Insights into the Nature of Solar Wind Discontinuities through the MADD Technique

Abstract Magnetohydrodynamics (MHD) discontinuities are widespread intermittent structures in space and astrophysical plasmas, whose jump conditions are ruled by the well-known Rankine–Hugoniot relations. Despite the long-term research on the solar wind discontinuity, its nature has still been poorly understood and intensely debated, due to the huge discrepancy between the discontinuity type distribution revealed by the single-spacecraft minimum variance analysis (MVA) and multispacecraft timing/triangulation techniques. This paper, utilizing the newly proposed maximum aligned directional derivative (MADD) technique, which estimates the normal of a discontinuity as the direction of the maximum spatial gradient of the magnetic field, conducts a statistical study of 94,648 discontinuities detected by the Magnetospheric Multiscale (MMS) spacecraft in the near-Earth solar winds (known as interplanetary discontinuities (IDs)) during 2017 October 9–2025 May 9. The geometric features, type distribution, and evolution with the solar activity and solar wind speed of those IDs are unveiled. The ID normal directions derived from MADD are then compared to timing and MVA results. This comparison demonstrates the deficiency of MVA in identifying IDs and explains how it occurs. This work thus establishes a true statistical picture of the solar wind discontinuities and could refresh our knowledge of the heliospheric turbulent environment.