Lanterna Rally

Author: Carolina Salas Matamoros

Publisher:

Published: 2016

Total Pages: 163

ISBN-13:

The solar corona is a highly dynamical medium: instabilities of the magnetic field, which structure the plasma, lead to the acceleration and heating ofcharged particles and to the ejection of large structures into the heliosphere, the Coronal Mass Ejections (CMEs). These ejected magnetic structures can interact with the Earth's magnetic field and thereby affect the plasma environment and the high atmosphere of the Earth. Studying the origin and propagation of CMEs is of interest for both astrophysics in general and space weather applications. The understanding of the basic processes is indeed a pre-requisite for developing prediction methods of potentially geo-effective disturbances based on observations of the solar corona.The CMEs are observed and studied primarily through coronographic images. The basic limitation of the coronagraph is that it shows the corona only in the plane of the sky, and blocks by necessity the view on the solar disk. But the geoeffectiveness of a CME depends crucially on the proximity to the Sun-Earth line and the measurements of the propagation speed, onset and early evolution of CMEs in the low corona are not accessible to coronographic observations. This thesis presents the study of CMEs in three different stages: (1) a case study of the CME evolution in the low corona and of its role in particle acceleration, (2) the relationship between the polarisation of the type IV radio emission associated with Earth-directed CMEs in the corona and the orientation of the magnetic field observed as the CMEs arrive at the Earth, and (3) the estimation of the travel times of CMEs to the Earth. Radio imaging with the Nancay Radioheliograph (NRH) suggest that radio images at metric wavelengths track the early evolution of CMEs well before they become visible in the corona. The examination of the CME evolution in the low corona developed in this work was illustrated through the study of the eruptive event on 26 April 2008, which offered a unique opportunity to investigate the physical link between a single well-identified CME, electron acceleration as traced by radio emission, and the production of solar energetic particles (SEPs) observed in space. We conduct a detailed analysis combining radio observations (NRH and Decameter Array, Wind/WAVES spectrograph) with remote-sensing observations of the corona in extreme ultraviolet (EUV) and white light as well as in-situ measurements of energetic particles near 1AU (SoHO and STEREO spacecraft). By combining images taken from multiple vantage points we were able to derive the time-dependent evolution of the 3D pressure front developing around the erupting CME. Finally, we identified, from the radio and SEP observations, three different particle acceleration regions associated to the evolution of the same CME, separated in longitude by about 140$^\circ$. The observations for this event showed that it is misleading to interpret multi-spacecraft SEP measurements in terms of one acceleration region in the corona.