Acceleration and transport of solar energetic particles in the inner heliosphere

A new era of spacecraft probing the inner heliosphere make now possible the study of the spatial distribution of solar energetic particle (SEP) events closer to the Sun. Recent missions, such as Solar Orbiter, along with the constellations of spacecraft near 1 au facilitate the study of the radial dependence of SEP parameters, such as the peak intensity and spectrum. In this work, we use the solar energetic electrons (SEE) measured by the MESSENGER mission from 2011 to 2015 to derive statistical results about the radial dependence of some SEE parameters, which are compared with the results from Solar Orbiter near its first nominal perihelion in March 2022.  The main conclusions are: (1) There is a wide variability in the radial dependence of the electron peak intensities, but on average and within uncertainties, the radial dependence can be expressed as R^-3, being R the heliocentric distance to the Sun. (2) Between near 0.3 au and 1 au, the energy spectrum of the near-relativistic electrons becomes softer.

We also analyse the relations between the solar activity and the SEE peak intensities measured by MESSENGER, STEREO and ACE spacecraft during 2010-2015. We investigate the 3D early kinematic profile of the CME and associated wave and determine their main morphological (size) and dynamic (propagation and expansion speeds, acceleration) properties and study their relationship with the particle (electron and proton) energies and timing measured in situ. A summary of the results, implications for the Space Weather research, and comparison with previous works is presented.