Detecting in-situ directional discontinuities in the solar wind at Mercury's Orbit

The analysis of directional discontinuities (DDs) in the solar wind provides insights for understanding its embedded structures, such as flux ropes and switchbacks (SBs).

We aim to investigate the occurrence and nature of DDs observed by BepiColombo (BC) close to Mercury’s orbit and to establish links between magnetic field measurements and plasma parameters. Specifically, we assess the potential of DDs as indicators of SBs and other solar wind structures.

We use the attitude gradient to detect discontinuities combined with minimum variance analysis to characterize their boundaries.

During the selected period between 5 and 16 October 2021, a total of 1136 DDs were identified, with 960 meeting the eigenvalue ratio criterion for classification. The majority (83%) were rotational discontinuities (RDs) or either discontinuities (EDs). Low compressibility (CB < 0.03) conditions yielded a higher proportion of RDs and EDs (94%). PICAM observations revealed significant ion energy enhancements and particle deflections correlated with magnetic field reversals, particularly during SBs structures with low compressibility.

The results confirm the suitability of attitude gradient-based methods for DD detection and the potential of CB and z as proxies for identifying quasi-Alfvénic structures. The combined analysis of magnetic and plasma data highlights the role of DDs as markers of SBs, advancing our understanding of their nature and prevalence in the solar wind at 0.34 AU.