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Radio emission observations from the Learmonth and Bruny Island radiospectrographs are analysed to determine the nature of a train of discrete,periodic radio \lq sparks\rq (finite-bandwidth, short-duration isolated radiofeatures) which precede a type II burst. We analyse extreme ultraviolet (EUV)imaging from SDO/AIA at multiple wavelengths and identify a series ofquasi-periodic rapidly-propagating enhancements, which we interpret as a fastwave train, and link these to the detected radio features. The speeds andpositions of the periodic rapidly propagating fast waves and the coronal massejection (CME) were recorded using running-difference images and time-distanceanalysis. From the frequency of the radio sparks the local electron density atthe emission location was estimated for each. Using an empirical model for thescaling of density in the corona, the calculated electron density was used toobtain the height above the surface at which the emission occurs, and thepropagation velocity of the emission location. The period of the radio sparks,$\delta t_\mathrm{r}$=1.78$\pm$0.04 min, matches the period of the fast wavetrain observed at 171 $\AA$, $\delta t_\mathrm{EUV}$=1.7 $\pm$ 0.2 min. Theinferred 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 calculatedheight of the radio emission (obtained from the density) matches the observedlocation of the CME leading edge. From the above evidence we propose that theradio sparks are caused by the quasi-periodic fast waves, and the emission isgenerated as they catch up and interact with the leading edge of the CME.

Observation of quasi-periodic solar radio bursts associated with propagating fast-mode waves