Observation of quasi-periodic solar radio bursts associated with propagating fast-mode waves⋆
1 Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, CV4 7AL, UK
2 Astronomical Observatory at Pulkovo of the Russian Academy of Sciences, 196140 St Petersburg, Russia
3 School of Space Research, Kyung Hee University, 446-701 Yongin, Gyeonggi, Korea
4 Space Research Institute (IKI) of Russian Academy of Sciences, Profsoyuznaya St. 84/32, 117997 Moscow, Russia
5 State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Zhongguancun Nanertiao 1, Haidian District, 100190 Beijing, PR China
6 International Space Science Institute, Zhongguancun Nanertiao 1, Haidian District, 100190 Beijing, PR China
7 Air Force Research Laboratories, Space Vehicles Directorate, Albuquerque, NM 87117, USA
Received: 9 March 2016
Accepted: 5 August 2016
Aims. Radio emission observations from the Learmonth and Bruny Island radio spectrographs are analysed to determine the nature of a train of discrete, periodic radio “sparks” (finite-bandwidth, short-duration isolated radio features) which precede a type II burst. We analyse extreme ultraviolet (EUV) imaging from SDO/AIA at multiple wavelengths and identify a series of quasi-periodic rapidly-propagating enhancements, which we interpret as a fast wave train, and link these to the detected radio features.
Methods. The speeds and positions of the periodic rapidly propagating fast waves and the coronal mass ejection (CME) were recorded using running-difference images and time-distance analysis. From the frequency of the radio sparks the local electron density at the emission location was estimated for each. Using an empirical model for the scaling of density in the corona, the calculated electron density was used to obtain the height above the surface at which the emission occurs, and the propagation velocity of the emission location.
Results. The period of the radio sparks, δtr = 1.78 ± 0.04 min, matches the period of the fast wave train observed at 171 Å, δtEUV = 1.7 ± 0.2 min. The inferred speed of the emission location of the radio sparks, 630 km s-1, is comparable to the measured speed of the CME leading edge, 500 km s-1, and the speeds derived from the drifting of the type II lanes. The calculated height of the radio emission (obtained from the density) matches the observed location of the CME leading edge. From the above evidence we propose that the radio sparks are caused by the quasi-periodic fast waves, and the emission is generated as they catch up and interact with the leading edge of the CME.
Key words: Sun: corona / Sun: oscillations / Sun: radio radiation / Sun: coronal mass ejections (CMEs) / methods: observational
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© ESO, 2016