Type III Solar Radio Bursts Perturbed by Coronal Shocks

Bo Li
School of Physics, University of Sydney

Iver Cairns
School of Physics, University of Sydney

Peter Robinson
School of Physics, University of Sydney

     Full text: Not available
     Last modified: July 26, 2011

Abstract
Type III solar radio bursts are observed to undergo sudden flux modifications - e.g., cutoffs, reductions, and intensifications - when type III electron beams traverse shocks in the upper corona or solar wind. The effects on type III bursts of coronal shocks are studied using large-scale kinetic simulations. The simulations incorporate the spatially localized increases in plasma density ne(r) and temperatures of electrons Te(r) and ions Ti(r) downstream of a shock. The density jump across a shock naturally results in a frequency gap in the dynamic spectrum of a type III burst, and sudden changes in the profiles of radio flux, frequency drift rate, and duration. The presence of plateaus in ne(r) or localized enhancements in Te(r) or/and Ti(r) also lead to the formation of intense, slowly-drifting structures in the spectrum. These predicted effects are caused by fundamental changes in the quasilinear and nonlinear processes producing the type III bursts, in response to the density and temperature variations. The simulations suggest that coronal type IIIs may provide new tools to probe localized structures in ne(r), or Te(r), or Ti(r), and be able to differentiate the structures in these plasma parameters. Furthermore, the intense and slowly-drifting fine structures resemble those of stria and type IIIb bursts, thus suggesting that some of these bursts may be produced by the effects of multiple coronal shocks located at different heights. The simulations also indicate that type III bursts may provide a useful tool to identify weak shocks in the corona and possibly in the solar wind, when these shocks produce weak or no type II solar radio bursts.