Shock Associated Radio Emission in the Solar Atmosphere

Thejappa Golla

Abstract

Solar and interplanetary type II bursts are distinguished from other radio burst activity by their long durations ranging from minutes to days, and by their characteristic slow drift from high to low frequencies. These radio emissions are attributed to collisionless shocks propagating radially outward in the solar atmosphere. Three steps are involved in type II emission process: (1) electron acceleration by collisionless shocks, (2) excitation of Langmuir waves  by the accelerated electrons, and (3) conversion of Langmuir waves into escaping radiation at $f_{pe}$ and $2f_{pe}$,where $f_{pe}$ is the electron plasma frequency. There remain many questions about the detailed physics of these steps. We address these issues by analyzing the ULYSSES URAP observations of type II radio burst activity and {\it in-situ} shock associated Langmuir and ion-acoustic-like wave activity, and ISEE-3 observations of shock associated energetic electrons and ions. Based on these analyses, and other type II studies using WIND and ISEE-3 spacecraft, we will examine the interaction between the radially propagating shock and enhanced density or magnetic field gradients associated with either a coronal mass ejection (CME), a corotating interaction region, or a propagating shock as the frequent cause for the production of type II radio emission. We provide quantitative estimates for these processes. We also investigate the linear coupling of Langmuir waves with electromagnetic radiation at $f_{pe}$ due to shock associated density gradients as one of the possible emission mechanisms for $f_{pe}$ emission.
 

    Authors: R. J. MacDowall

  Organization: University of Maryland
     Telephone: 301-286-3390
           Fax: 301-286-1681
        e-mail: golla@urap.gsfc.nasa.gov
       Address: Department of Astronomy
   University of Maryland
   College Park MD 20742