Solar Physics

, 293:41 | Cite as

Spectropolarimetric Observations of Solar Noise Storms at Low Frequencies

  • V. Mugundhan
  • R. Ramesh
  • C. Kathiravan
  • G. V. S. Gireesh
  • Aathira Hegde


A new high-resolution radio spectropolarimeter instrument operating in the frequency range of 15 – 85 MHz has recently been commissioned at the Radio Astronomy Field Station of the Indian Institute of Astrophysics at Gauribidanur, 100 km north of Bangalore, India. We describe the design and construction of this instrument. We present observations of a solar radio noise storm associated with Active Region (AR) 12567 in the frequency range of \({\approx}\,15\,\mbox{--}\,85~\mbox{MHz}\) during 18 and 19 July 2016, observed using this instrument in the meridian-transit mode. This is the first report that we are aware of in which both the burst and continuum properties are derived simultaneously. Spectral indices and degree of polarization of both the continuum radiation and bursts are estimated. It is found that
  1. i)

    Type I storm bursts have a spectral index of \({\approx}\,{+}3.5\),

  2. ii)

    the spectral index of the background continuum is \({\approx}\,{+}2.9\),

  3. iii)

    the transition frequency between Type I and Type III storms occurs at \({\approx}\,55~\mbox{MHz}\),

  4. iv)

    Type III bursts have an average spectral index of \({\approx}\,{-}2.7\),

  5. v)

    the spectral index of the Type III continuum is \({\approx}\,{-}1.6\), and

  6. vi)

    the degree of circular polarization of all Type I (Type III) bursts is \({\approx}\,90\%\) (\(30\%\)).

The results obtained here indicate that the continuum emission is due to bursts occurring in rapid succession. We find that the derived parameters for Type I bursts are consistent with suprathermal electron acceleration theory and those of Type III favor fundamental plasma emission.


Corona, radio emission Polarization, radio Radio bursts, meter-wavelengths and longer (m, dkm, hm, km) Radio bursts, Type I Radio bursts, Type III Instrumentation and Data Management 



It is a pleasure to thank the workshop staff in the Gauribidanur Observatory for assistance in the building of the array, and the observers there for effectively carrying out the observations reported in this work. We thank the referee for their comments that helped us to present the results in a better manner. V. Mugundhan would like to thank the CASPER consortium for providing open-source signal-processing libraries, M. Rajesh for providing the dual-frequency images with the GRAPH, K. Hariharan for fruitful discussions, and Anshu Kumari for thoroughly proofreading the manuscript. The portion of work carried out by A. Hegde was during her time as an Indian Academy of Sciences Summer Intern.

Disclosure of Potential Conflicts of interest

We declare that there are no conflicts of interest for the work presented here.


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Copyright information

© Springer Science+Business Media B.V., part of Springer Nature 2018

Authors and Affiliations

  • V. Mugundhan
    • 1
  • R. Ramesh
    • 1
  • C. Kathiravan
    • 1
  • G. V. S. Gireesh
    • 1
  • Aathira Hegde
    • 2
  1. 1.Indian Institute of AstrophysicsBangaloreIndia
  2. 2.Indian Institute of Space TechnologyThiruvananthapuramIndia

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