The interplanetary magnetic structure that guides solar relativistic particles

• Autores: Masson, S.; Démoulin, P.; Dasso, S.; Klein, K.-L.
• Año de publicación: 2012
• Idioma: inglés
• Tipo de recurso: artículo
• Fuente: Astron. Astrophys. 2012;538
• Materia: methods: data analysis; solar-terrestrial relations; Sun: heliosphere; Activity cycles; Arrival time; Energetic particle measurement; Energetic particles; Fast solar winds; High-energy particles; In-situ measurement; Interplanetary coronal mass ejections; Interplanetary magnetic fields; Methods:data analysis; Neutron monitors; Parker spiral; Path length; Pitch-angle scattering; Plasma parameter; Radio bursts; Relativistic particles; Relativistic solar particles; Solar activity; Solar-terrestrial relations; Transient structure; Velocity dispersion; Electron beams; Magnetic bubbles; Magnetic fields; Magnetic structure; Magnetoplasma; Relativity; Solar energy; Solar radiation; Solar system; Solar wind; Interplanetary spacecraft
• Institución: Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales

Context. Relating in-situ measurements of relativistic solar particles to their parent activity in the corona requires understanding the magnetic structures that guide them from their acceleration site to the Earth. Relativistic particle events are observed at times of high solar activity, when transient magnetic structures such as interplanetary coronal mass ejections (ICMEs) often shape the interplanetary magnetic field (IMF). They may introduce interplanetary paths that are longer than nominal, and magnetic connections rooted far from the nominal Parker spiral. Aims. We present a detailed study of the IMF configurations during ten relativistic solar particle events of the 23rd activity cycle to elucidate the actual IMF configuration that guides the particles to the Earth, where they are measured by neutron monitors. Methods. We used magnetic field (MAG) and plasma parameter measurements (SWEPAM) from the ACE spacecraft and determined the interplanetary path lengths of energetic particles through a modified version of the velocity dispersion analysis based on energetic particle measurements with SoHO/ERNE. Results. We find that the majority (7/10) of the events is detected in the vicinity of an ICME. Their interplanetary path lengths are found to be longer (1.5-2.6 AU) than those of the two events propagating in the slow solar wind (1.3 AU). The longest apparent path length is found in an event within the fast solar wind, probably caused by enhanced pitch angle scattering. The derived path lengths imply that the first energetic and relativistic protons are released at the Sun at the same time as electron beam emitting type III radio bursts. Conclusions. The timing of the first high-energy particle arrival on Earth is mainly determined by the type of IMF in which the particles propagate. Initial arrival times are as expected from Parker's model in the slow solar wind, and significantly longer in or near transient structures such as ICMEs. © 2012 ESO.
Fil:Dasso, S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.