Shock waves in the solar corona and their radio emission

Abstract

In the solar corona shock waves can be generated by coronal mass ejections and/or solar flares. They manifest themselves in solar type II radio bursts. A sample of 25 such radio bursts is investigated concerning their spectral features. Assuming that the type II burst radiation is generated in the vicinity of the transition region of coronal shock waves as indicated by plasma wave measurements at interplanetary shock waves the instantaneous bandwidth reflects the density jump of the shock. Comparing the observational results with the evaluation of the Rankine-Hugoniot relations of MHD shock waves solar type II bursts should be regarded as being generated by weak supercritical, quasi-parallel fast magnetosonic shock waves in the solar corona. As well-known from Earth's bow shock, quasi-parallel collisionless shocks are associated by strong magnetic field turbulence, e.g., in form of short large amplitude magnetic field structures (SLAMS). Assuming that these features also appear at quasi-parallel shock waves in the solar corona, electrons can be accelerated at such shock waves due to drift acceleration within SLAMS up to suprathermal energies. These electrons are able to excite Langmuir waves which can convert into radio waves observed as solar type II bursts.