Behavior of energetic particles in magnetic switchbacks observed by ISOIS in early PSP orbits

Abstract:

The effect of interplanetary magnetic-field fluctuations on the propagation of energetic particle is not well understood. Observations at 1 au and initial Parker Solar Probe orbits have confirmed that measured energetic particle fluxes are statistically associated with “rough” magnetic fields, as measured by the Partial Variance of Increments (PVI) method. This has been interpreted as association due to trapping within magnetic flux tubes, or near their boundaries. 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. An additional noteworthy observation by Parker Solar Probe in early orbits is the appearance of sporadic large reversals in the magnetic field direction relative to the regional dominant polarity, a phenomenon called “switchback.” Other studies have observed that the sense of propagation of Alfvenic wave packets, as well as the direction of electron strahl, reverse direction along with the magnetic field in switchbacks. Here we explore whether the energetic protons, which reside at much higher energies than the thermal population, follow the magnetic field lines when these polarity reversals occur. Initial results using data from the ISOIS EPI-Lo instrument indicate that the energetic protons typically do not reverse sign in magnetic switchbacks. Possible reasons for this disparity will be discussed.