Statistics of Energetic Particles in the first Parker Solar Probe Orbit: Correlations and Association with Magnetic Structures
Résumé
Observations at 1 au have confirmed that measured energetic particle fluxes are statistically associated with "rough" magnetic fields, as measured by the Partial Variance of Increments (PVI) method [1]. This has been interpreted as association due to trapping within magnetic flux tubes, or near their boundaries[2,3]. However it has so far remained unclear if this is a transport effect, with particles energized at a distant location, perhaps by shocks or reconnection, or, on the other hand, if the particles might experience local energization, or re-acceleration. Parker Solar Probe (PSP), even in its first orbit, offers a unique opportunity to examine this phenomenon closer to the corona. There, if due to transport, the effect may be recorded closer to the sources, or earlier in the acceleration process. If the effect is due to local acceleration, the parameters in which it is observed will likely be much different than at 1 au. As a first step, we analyze the separate correlation properties of the magnetic signal recorded by the MAG instrument, and the energetic particles recorded by the ISOIS instruments. We find that FGM observations show a power-law distribution of waiting times in the magnetic-field PVI, while an analysis of ISOIS counts also shows power laws, indicating a correlated (non-Poisson) distribution. Preliminary analysis of low energy ISOIS data suggests results consistent with the Tessein et al studies [2,3], while results of higher energy count distributions conditioned on PVI are less clear. A more complete understanding of these statistical distributions will provide valuable insights into the origin and propagation of solar energetic particles, a picture that should become clear with future PSP orbits. Research partially supported by a subcontract to NASA NNN06AA01C. [1] A. Greco, W. H. Matthaeus, S. Perri, K. T. Osman, S. Servidio, M. Wan and P. Dmitruk, Space Sci Rev., 214, 1 (2018) [2] J. A. Tessein, D. Ruffolo, W. H. Matthaeus et al., ApJ, 812, 68 (2015), https://doi.org/10.1088/0004-637X/812/1/68 [3] J. A. Tessein, D. Ruffolo, W. H. Matthaeus, and M. Wan. Geophys. Res. Lett., 43:3620, (2016).