Abstracts

1) Study of the formation and the evolution of Coronal Mass Ejection driven shocks and their role in particle acceleration

S. Perri, G. Zimbardo, G. Prete

One of the outstanding scientific questions in space physics, is how charged particles are accelerated up to supra-thermal energies. Candidates for particle acceleration are the shocks driven by eruptive phenomena in the solar corona as the coronal mass ejections (CMEs). Thanks to the joint combination between in-situ (as the MAG, SWA, EPD) and remote sensing (EUI, METIS) instruments on board Solar Orbiter and to its vicinity to the Sun, we will have the opportunity to study, with unprecedent precision, the onset of CMEs and the properties of the induced shocks propagating in the interplanetary medium. Thus, parameters as the sonic Mach number and the compression ratio (both when shocks form in the corona and propagate in the interplanetary space) will give a quantitative enstimation of the shocks evolution and their capability to accelerate particles. Being close to the source of acceleration, it will be possible to separate the energetic particle "seed" population without any mixing due to effects of propagation in the heliosphere.

2) Acceleration and propagation of solar energetic particles

Monica Laurenza

In situ observations from the Energetic Particle Detector (EPD) onboard Solar Orbiter (SolO) can be exploited to assess the poorly known energetic particle radiation environment in the inner Heliosphere, as well as to investigate the phenomena involved in the acceleration and propagation of solar energetic particles (SEPs), that were difficult to resolve from prior observations. Synergies with SolO remote sensing observations will be vital to perform a thorough characterization of the SEP associated solar sources (flares and CMEs). Moreover, by combining EPD and Solar Wind Analyser data it will be possible to characterize and investigate the transition between thermal and supra-thermal particles of the solar wind.

3) Near-Sun study of the pitch-angle scattering of He+ pick-ions with the SWA Solar orbiter instrument

G. Zimbardo and S. Perri

A detailed understanding of suprathermal particles pitch-angle scattering is strongly needed both for shock acceleration models and for SEPs propagation. Helium neutrals of interstellar origin can propagate against the solar wind and into the heliosphere and then be ionized either by electron-impact or by photoionization, forming the so-called pick-up ions. Helium pick-up ions He+ are also observed close to the Sun at less than 0.3 AU. Preferred place for this study is the helium gravitational focusing cone between 0.1 and 0.3 AU (Gershman et al. 2014). Solar Orbiter gives the chance to study He+ pitch-angle distribution close to injection, as well as the pitch-angle scattering process. This is an ideal target for Solar Orbiter SWA suite, which is able to obtain the 3D velocity distribution of alpha particles. The analysis will be completed by the MAG magnetic field data which will determine the level of magnetic turbulence in resonance with He+, therefore allowing to check the theories of pitch-angle scattering.