Radio emissions from solar active regions

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45 Scopus citations


Solar active region coronae are known for strong magnetic fields permeating tenuous plasma, which makes them an ideal astronomical laboratory for magnetohydrodynamics research. It is, however, relatively less known that this physical condition also permits a very efficient radiation mechanism, gyro-resonant emission, produced by hot electrons gyrating in the coronal magnetic field. As a resonant mechanism, gyro-emission produces high enough opacity to fully reveal the coronal temperature, and is concentrated at a few harmonics of the local gyrofrequency to serve as an excellent indicator of the magnetic field. In addition, the polarization of the ubiquitous free-free emission and a phenomenon of depolarization due to mode coupling extend the magnetic field diagnostic to a wide range of coronal heights. The ability to measure the coronal temperature and magnetic field without the complications that arise in other radiative inversion problems is a particular advantage for the active region radio emissions available only at these wavelengths. This article reviews the efforts to understand these radiative processes, and use them as diagnostic tools to address a number of critical issues involved with active regions.

Original languageEnglish (US)
Pages (from-to)73-102
Number of pages30
JournalSpace Science Reviews
Issue number1-4
StatePublished - Dec 2007

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Solar magnetic fields
  • Solar radio emission
  • Sun: solar corona


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