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Shock Signatures of the Successive Type-II Solar Radio Bursts at Meter Wavelength

V. Vasanth

TL;DR

The paper investigates the origin of successive type-II solar radio bursts observed on 31 July 2012 by analyzing a single CME-driven shock interacting with coronal streamer structures. It combines high-cadence radio spectra from BIRS with EUV/white-light imaging from STEREO and LASCO and applies multiple coronal density models to map radio frequencies to heights and speeds. The results show that the first type-II burst originates at the CME shock front, while the second results from a shock– streamer interaction along the CME flank, both driven by the same CME and exhibiting distinct drift rates corresponding to different coronal regions. This work highlights the role of streamer interactions in generating secondary type-II components and provides a practical framework for diagnosing coronal densities and magnetic fields from radio observations.

Abstract

The successive type-II solar radio bursts observed on 31 July 2012 by the Bruny Island Radio Spectrometer (BIRS) in the frequency range between 62 - 6 MHz is reported and analyzed. The first type-II radio burst shows clear fundamental and harmonic band structures, while only one band is observed for the second type-II radio burst and is considered as the harmonic band. The first type-II radio burst is observed in the frequency range of 57 - 27 MHz between 00:03 - 00:09 UT at the harmonic band. The second type-II burst is observed between 00:18 - 00:27 UT in the frequency range of 43 - 17 MHz. The type-II radio bursts are associated with a C6 class flare located at the south-eastern limb (S24E87) and a CME observed from STEREO and LASCO observations. The EUVI signatures of the CME is observed in the ST-B EUVI FOV between 23:56 (on 30 July 2012) to 00:06 UT (on 31 July 2012), and are observed in the ST-B COR1 FOV between 00:10 - 00:35 UT moving within an average speed of 725 + or - 101 km/s. The CME is observed in the LASCO C2 FOV after 00:12 UT as a partial halo CME moving with an average speed of 486 km/s. The height-time plot shows that the first type-II radio burst was formed by the CME-shock along the shock front and the second type-II radio burst along the shock-dip structure, probably the dip structure results from the shock transiting across the high dense streamer structure. The successive type-II bursts are most likely produced by the single CME shock and their interactions with the streamer structures. The first type-II radio burst by the CME shock and the second type-II radio burst by the CME shock-streamer interactions.

Shock Signatures of the Successive Type-II Solar Radio Bursts at Meter Wavelength

TL;DR

The paper investigates the origin of successive type-II solar radio bursts observed on 31 July 2012 by analyzing a single CME-driven shock interacting with coronal streamer structures. It combines high-cadence radio spectra from BIRS with EUV/white-light imaging from STEREO and LASCO and applies multiple coronal density models to map radio frequencies to heights and speeds. The results show that the first type-II burst originates at the CME shock front, while the second results from a shock– streamer interaction along the CME flank, both driven by the same CME and exhibiting distinct drift rates corresponding to different coronal regions. This work highlights the role of streamer interactions in generating secondary type-II components and provides a practical framework for diagnosing coronal densities and magnetic fields from radio observations.

Abstract

The successive type-II solar radio bursts observed on 31 July 2012 by the Bruny Island Radio Spectrometer (BIRS) in the frequency range between 62 - 6 MHz is reported and analyzed. The first type-II radio burst shows clear fundamental and harmonic band structures, while only one band is observed for the second type-II radio burst and is considered as the harmonic band. The first type-II radio burst is observed in the frequency range of 57 - 27 MHz between 00:03 - 00:09 UT at the harmonic band. The second type-II burst is observed between 00:18 - 00:27 UT in the frequency range of 43 - 17 MHz. The type-II radio bursts are associated with a C6 class flare located at the south-eastern limb (S24E87) and a CME observed from STEREO and LASCO observations. The EUVI signatures of the CME is observed in the ST-B EUVI FOV between 23:56 (on 30 July 2012) to 00:06 UT (on 31 July 2012), and are observed in the ST-B COR1 FOV between 00:10 - 00:35 UT moving within an average speed of 725 + or - 101 km/s. The CME is observed in the LASCO C2 FOV after 00:12 UT as a partial halo CME moving with an average speed of 486 km/s. The height-time plot shows that the first type-II radio burst was formed by the CME-shock along the shock front and the second type-II radio burst along the shock-dip structure, probably the dip structure results from the shock transiting across the high dense streamer structure. The successive type-II bursts are most likely produced by the single CME shock and their interactions with the streamer structures. The first type-II radio burst by the CME shock and the second type-II radio burst by the CME shock-streamer interactions.
Paper Structure (7 sections, 3 equations, 6 figures, 1 table)

This paper contains 7 sections, 3 equations, 6 figures, 1 table.

Table of Contents

  1. Introduction
  2. Overview of the Event
  3. Radio Observations
  4. EUV-White light eruptive structures
  5. Results
  6. Discussion
  7. Conclusions

Figures (6)

  • Figure 1: (a) The radio dynamic spectrum of the successive type-II radio bursts recorded by the BIRS (62 $\--$ 6 MHz) on 31 July 2012 between 00:00 UT $\--$ 00:30 UT, (b) GOES X-ray profile at 0.5 $\--$ 4 and 1 $\--$ 8 Å.
  • Figure 2: (a) Relative location of the twin spacecraft (STEREO) and the Earth, (b) - (c) sequence of the ST-B EUVI running difference images showing the eruptive structure at 195 Å, (d) the CME and streamer structure observed in the LASCO C2 difference image, (e) - (h) the temporal and structural evolution of CME observed by the ST-B COR1 running difference images. The red arrow at (b) - (h) indicates the CME structure, the white arrow at (d) shows the brightness enhancement observed partially along the CME front and at (f) indicates the dip structure.
  • Figure 3: (a) The PFSS magnetic field lines shown over the (a) LASCO-EIT image and (b) LASCO C2 image. The major part of the CME passes through the streamer structure.
  • Figure 4: Temporal evolution of the electron density profile as a function of the distance obtained from the ST-B COR1 $P_B$ data at 00:25 UT.
  • Figure 5: The heights of shock and flux rope measured using the Pythea (GCS and Ellipsoidal models)
  • ...and 1 more figures