Evolution of Coronal and Interplanetary Shock Waves Inferred from a Radio Burst
Studying the evolution of the source of a radio burst, which is recognized as a shock wave, is important for understanding its generation mechanism and predicting its hazards. Estimating the kinematics of radio-burst sources using electron-density models is not easy. In this article, the kinematics of the Type-II radio-burst source is estimated without using electron-density models by studying the density variation along the leading surface of the coronal mass ejections (CMEs) (hereafter ejecta) during Type-II radio-burst emission. This technique is valid for analyzing the Type-II radio-burst spectrum in metric and DH ranges, from which we can infer ejecta propagation from the corona into interplanetary space. It is found that the Type-II radio burst can be described by the Sedov–Taylor blast-wave equation by matching the calculated theoretical frequencies with that observed by the RAD1 and RAD2 receivers. The theoretical model showed a good fit with the observed spectra of Type-II radio bursts of different Type-II events. The analysis was consistent with the previous work regarding the conditions of the Sedov–Taylor equation and statistical studies of the density variation on the surface area of an interplanetary CME. The kinematics of a Type-II radio-burst source and the temporal variation of its energy are estimated during the Type-II radio-burst emission. The results of the two cases studied show that the energy of ejecta degraded by \(\approx 14\% \) of its initial energy at the beginning of metric Type-II radio emission on 16 March 2016, while the energy of ejecta degraded by \(\approx 86\%\) and \(\approx 20 \% \) for DH Type-II radio burst as recorded by RAD1 and RAD2 on 7 November 2004, respectively. The analysis shows that the radial speed of the blast wave is lower than its transversal speed along the surface of ejecta and extends to a small fraction of R⊙ from its source point on the ejecta. The magnetic-field strength of the ejecta and the ambient medium are estimated during the Type-II radio-burst emission. This study emphasizes that the emission of a blast wave from the reconnection sites within the ejecta is one of the processes that degrades the energy of ejecta during their propagation.
KeywordsType II radio burst: source and dynamic spectrum CMEs
I am grateful to Ayman Mahrous, Helwan University in Egypt, Bojan Vršnak, Hvar Observatory in Croatia, and Alexander Nindos, University of Ioannina in Greece for their guidance and support. Thanks to the staff of the Learmonth solar radio spectrograph for their data and the NASA Staff of Wind/WAVES for their data.
- Cook, N.B.: 2010, Analytical proof of the Taylor equation including Taylor’s constant \(S\gamma\) which previously required numerical integration, with applications. http://vixra.org/pdf/1003.0259v1.pdf.
- Cowling, T.G.: 1953, The Solar System, vol. 1: The Sun. University of Chicago Press, Chicago, 533. Google Scholar
- Emslie, A.G., Kucharek, H., Dennis, B.R., Gopalswamy, N., Holman, G.D., Share, G.H., Vourlidas, A., Forbes, T.G., Gallagher, P.T., Mason, G.M., Metcalf, T.R., Mewaldt, R.A., Murphy, R.J., Schwartz, R.A., Zurbuchen, T.H.: 2004, Energy partition in two solar flare/CME events. J. Geophys. Res., Space Phys. 109(A10). Google Scholar
- Gopalswamy, N.: 2006, Coronal mass ejections and type II radio bursts. In: Gopalswamy, N., Mewaldt, R., Torsti, J. (eds.) Solar Eruptions and Energetic Particles, Geophys. Monograph. Ser.165, AGU, Washington, 207. Google Scholar
- Nelson, G.J., Melrose, D.B.: 1985, Type II bursts. In: MacLean, D.J., Labrum, N.R. (eds.) Solar Radiophysics: Studies of Emission from the Sun at Meter Wavelengths, Cambridge University Press, Cambridge, 333. Google Scholar
- Sedov, L.I.: 1946, Propagation of strong shock waves. J. Appl. Math. Mech.10(564), 241. Google Scholar
- White, S.M.: 2007, Solar radio bursts and space weather. Asian J. Phys.16, 189. Google Scholar