Spatial distribution of solar energetic particles in the inner heliosphereinfluence of solar origin and interplanetary context

Abstract

In this thesis work we present a thorough study of the spatial, both longitudinal and radial, distribution of solar energetic particles in the inner heliosphere. We pay special attention to the influence of the solar origin and of the interplanetary context. For this purpose, we perform a detailed analysis of the widespread solar energetic particle (SEP) event on 2013 August 19, which particle spread was measured by several spacecraft radially and longitudinally distributed in the heliosphere, and of the coronal mass ejection (CME) associated to the particle event. We also carry out a statistical study of the electron events measured by the MESSENGER mission (near 0.3 au from the Sun) from February 2010 to May 2015, including the SEP event in August 2013. Some of these events were also observed by STEREO (near 1 au) and near-Earth missions, when in close nominal magnetic connection with MESSENGER. Similarly, we include a sample of events measured by Solar Orbiter around its first perihelion in the nominal phase of the mission, near 0.32 au, when Solar Orbiter was in close nominal magnetic connection with near 1 au spacecraft. The main findings of the thesis work are as follows: the correlations of the electron peak intensities with the solar source parameters, such as the flare intensity or the CME-driven shock speed, based on near 0.3 au particle measurements are stronger than those found in previous studies using near 1 au data. The main source of the acceleration of particles in gradual, wide, and large events is most likely the CME-driven shock. There is a wide variability in the radial dependence of the electron peak intensities between near 0.3 au and 1 au, with a high influence of the interplanetary context, as shown in the August 2013 event. However the mean ∝ R -3 dependence found in previous studies, being R the radial distance to the Sun, is confirmed. The mean spectral index δ found with MESSENGER data is much harder than in previous studies using near 1 au measurements. The systematic softening of the spectral indices of the energetic electrons between near 0.3 au and near 1 au locations is likely related to interplanetary scattering affecting the particle propagation, as found in the study of the August 2013 SEP event.