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Single-spacecraft Identification of Flux Tubes and Current Sheets in the Solar Wind

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Authors:

F. Pecora, A. Greco, Q. Hu, S. Servidio, A. Chasapis, W. H. Matthaeus

In this work we present a novel technique, based on two consolidated models, for describing and visualising the local topology of the magnetic field solar wind using single-spacecraft data. The Grad-Shafranov (GS) reconstruction method provides a two-dimensional map of the magnetic field surrounding the spacecraft trajectory, while the Partial Variance of Increments (PVI) technique is able to identify coherent magnetic structures, such as current sheets. We applied this combined technique to one month of magnetic field data measured by Wind satellite at 1 AU. In this stream we selected the flux rope events, that are structures with cylindrical symmetry and a relatively strong magnetic field along the symmetry axis. These flux tubes are quite large structures (a fraction of AU) and have a complex inner structure and they interact each other while moving in the Solar Wind.

On the left a sketch of interacting flux tubes with the path of a spacecraft passing through them. On the right reconstructed flux ropes for Wind January 2016 in the local frame (x,y), with the z-axis representing the cylindrical axis of the flux rope. Magnetic potential contour lines with filled colour plots of the current density J[A/m2] in the z-direction. The dashed lines at y = 0 are the projection of the spacecraft path on the flux rope cross section. The yellow stars and the green circles represent the start and the end time of current sheets, respectively. The x-axis of the figures represent the observation period, that can be transformed into spatial dimensions (see the ruler inside the plots) applying Taylor hypothesis.

These inner and outer interactions can possibly generate sites of magnetic reconnection where strong current sheets appear. What we observed from the reconstruction is that a quasi-two-dimensional turbulence emerges as a sea of nested magnetic islands with current sheets located mostly at their boundaries. The method shows great promise for visualising and analysing single-spacecraft data from missions such as Parker Solar Probe and Solar Orbiter, as well as 1 AU SpaceWeather monitors such as ACE, Wind, and IMAP.

Publication: Pecora F., Greco A., Hu Q., Servidio S., Chasapis A. G., Matthaeus W. H., 2019, ApJL, 881, L11. doi:10.3847/2041-8213/ab32d9
https://iopscience.iop.org/article/10.3847/2041-8213/ab32d9