Formation and Properties of Tangential Discontinuities in Three-dimensional Compressive MHD Turbulence

Tangential discontinuities (TDs) are observed to be ubiquitous in solar wind turbulence. In this study, we investigate the formation and properties of TDs in drivencompressive magnetohydrodynamic (MHD) turbulence with an imposed uniform guide field. By detecting sharp interfaces of magnetic pressure and thermal pressure, with total pressure balanced across them, TDs are identified in the simulated turbulence and are seen to separate distinct plasma regions and magnetic field regions, behaving as the walls of the different flux tubes. Across an identified TD, the temperature, with an enhancement at it, experiences the large jumps, while the jumps of the density are not typical. Its 3D structure and temporal evolution point out that mutual approaching, squeezing, and separating of flux tubes with different turbulent plasma results in the formation and collapse of the identified TD, with its lifetime about 4.5 hours. Through isolating each of the formed TDs from the background in the spatial dimensions, and also tracking each of them through time, from their formation to their collapse, it is found that the TDs display a multiscale nature, with most of them appearing 2D geometry. Their characteristic length can be as large as 2 × 10^3 Mm, their characteristic width comes to an averaged value of about 200 Mm, and their volume has a maximum value of about 10^7 Mm^3. For most of the TDs, the energy dissipative rate is about 10^7 J s^-1. The number of the TDs reduces fast with increasing their characteristic length, characteristic width, and volume. As the energy dissipative rate raises, the number of the TDs first increases, and then decreases rapidly. The lifetimes of the TDs extend from about 0.9 hours to about 11.8 hours, with fewer TDs surviving longer lifetime. Their lifetimes are thus far smaller that the time that the solar wind takes from the Sun to 1 AU, which indicates that TDs observed by in situ satellites at 1 AU are more likely to be generated by local turbulence.