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.

We perform a statistical investigation of the geometric features of interplanetary discontinuities (IDs) in the near-Earth solar wind and magnetosheath, by utilizing 14 months of Magnetospheric Multiscale mission data. 117,669 IDs are collected, including 108,049 events in the solar wind and 6399 events in the magnetosheath, with the remnant in the magnetosphere or near the bow shock/magnetopause. We find the following: (1) the ID occurrence rate is 17.0 events hr−1 in the solar wind and 5.5 events hr−1 in the magnetosheath, (2) the field rotation angles during ID crossings in the magnetosheath exhibit a two-exponential distribution with a breakpoint at 50°, which is not observed for IDs in the solar wind, (3) the magnetosheath IDs with small field rotation angles tend to be clustered, (4) by classifying the IDs into rotational discontinuities (RDs), tangential discontinuities (TDs), either TDs or RDs (EDs), and neither TDs nor RDs (NDs), we estimate RD:TD:ED:ND = 68%:5%:20%:7% in the solar wind, and RD:TD:ED:ND = 15%:44%:18%:23% in the magnetosheath, (5) the occurrence rates of RDs and TDs are, respectively 7.95 and 0.58 events hr−1 in the solar wind, and 0.57 and 1.60 events hr−1 in the magnetosheath, (6) RDs are more likely to propagate antisunward in the plasma rest frame, especially in the magnetosheath, and (7) the average thicknesses of the RDs and TDs are estimated, respectively, as 10.4 and 8.1 proton gyroradii (r p ) in the solar wind, and 17.4 and 5.0 r p in the magnetosheath. This work can improve our understanding of IDs’ interaction with the terrestrial bow shock.

Using data from the Cluster mission and the First-Order Taylor Expansion method, we investigate the spiral magnetic nulls nested in the diffusion region of turbulent reconnection in the magnetotail. We particularly focus on the relation between the magnetic null topologies and currents, which can be decomposed into a component perpendicular to spine (j ⊥) and a component parallel to spine (j ∥). We find that (1) the currents surrounding the spiral nulls are mainly contributed by j ∥; (2) the null with large (j ⊥) and small spine-fan angle (θ), which are predicted by traditional linear theory, does not exist in the turbulent diffusion region; (3) the background current j b plays an important role in determining the direction of the currents around spiral nulls and consequently the orientation of the magnetic null structures; and (4) the spiral nulls with strong current (large magnitude j ) tend to degenerate into 2D configurations, whereas the nulls with weak currents retain the 3D features. Since the spiral magnetic nulls are crucial for the energy dissipation during the turbulent reconnection process, all of these results can provide important information for better understanding 3D turbulent reconnection.