Rapid fluctuations in the position, size, and brightness of intense solar metre-wave radio sources

Abstract

A comparison of quiescent type I solar radio sources with concurrent intense impulsive type III, V, and type II sources shows that whereas the type I sources are usually small and stable the type III, V, and II sources are usually large and unstable. We conclude that the large size and variability of the type III, V, and II radio sources cannot be attributed to instrumental error or ionospheric refraction but must instead reflect the size and variability of the coronal structures on which they arise.

Evidence for Super-Alfvénic Oscillations in Solar Type III Radio Burst Sources

“…Temporal variation in the location of burst sources have been reported by earlier authors (Duncan 1985;Kontar et al 2017). Figure 8 (left panel) shows the observed locations of the burst sources at 118.8 MHz, close to the centre of the observation band.…”

“…This has lead to the suggestions that the sources of type III emissions must themselves comprise multiple sites of emission (e.g. Mercier 1975;Pick et al 1980;Duncan 1985). The large intrinsic sizes of sources of burst emission from this work provide further evidence for this possibility.…”

“…The origin of many of the observed properties of type III burst sources have been a matter of active debate. While some groups argued that the observed source properties are primarily driven by strongly divergent coronal B, variability of supra-thermal electron beams and other physical conditions at the burst site (Sheridan et al 1972;Pick et al 1980;Duncan 1985), others argued for the dominance of wave propagation effects -namely ducting, scattering and refraction (Steinberg et al 1971;Robinson 1983;Bastian 1994;Arzner & Magun 1999;Wu et al 2002). It is widely believed that the second-scale QPOs observed in type III burst intensity must arise due to a cause intrinsic to the source of emission, rather than radio wave propagation effects through the turbulent corona.…”