Browsing by Author "Räsänen, Juska"

Coronal mass ejections (CMEs) are large-scale eruptions of plasma entrained in a magnetic field. They occur in the solar corona, and from there they propagate into interplanetary space along with the solar wind. If a CME travels faster than the surrounding solar wind, a shock wave forms. Shocks driven by CMEs can act as powerful accelerators of charged particles. When charged particles like electrons are accelerated, they emit electromagnetic radiation, especially in the form of radio waves. Much of the radio emission from CMEs comes in the form of solar radio bursts. Traditionally solar radio bursts are classified into five types, called type I–V bursts, based on their characteristics and appearance in a dynamic spectrum. Of these five types of bursts, especially type II radio bursts are believed to be signatures of shock waves in the corona and interplanetary space. There are, however, also radio bursts associated with CMEs and shocks that do not fit the description of any of the five standard types of radio bursts. In this thesis three moving radio bursts associated with a CME that erupted on May 22, 2013 are identified and studied in detail. The characteristics of the bursts do not match those of the usual five types of solar radio bursts. The aim of the work is to ascertain the emission mechanism that causes the observed radio bursts, as well as locate the sites of electron acceleration that are the sources of the emission. The kinematics and the spectral features of the emission are studied in order to find answers to these questions. Analysis of the spectral features of the moving bursts showed that the bursts were emitted via plasma emission. Analysis of the kinematics revealed that the moving radio bursts originated unusually high up in the corona from the northern flank of the CME. The CME studied in this work was preceded by another one which erupted some hours earlier, and the disturbed coronal environment likely caused the radio emission to be emitted from an unusual height. It was found that the bursts likely originated from electrons accelerated at the shock driven by the CME.