SummaryThe relationship of radio bursts of spectral type III to solar flares is investigated by comparing simultaneous optical and radio observations. Over 300 flares are examined, 85 per cent. of which are microflares (class 1-). About 20 per cent. of the flares are associated with type III events, while more than 60 per cent. of the bursts recorded occur during the lifetime of a flare. These bursts tend to occur near the beginning of the flare or even to precede it slightly.The degree of association varies markedly over a period of days. Flares occurring in certain activity regions show a high degree of correlation with bursts, while those occurring in other regions show little or no correlation. The probability of a burst accompanying a flare is greater for larger flares. It is essentially the same for flares on the easteru limb as for flares in the centre of the disk, implying a wide cone of escape for type III radiation. There is an apparent deficit for flares on the westeru hemisphere. The occurrence of a surge with a flare appears to increase somewhat the likelihood of an associated radio event.

By using a combination of X-ray (HXIS), Hc~ (Haleakala), white-light corona (Solwind), and zodiacal light (Helios) images on 21-22 May, 1980 we demonstrate, and try to explain, the co-existence of a coronal mass ejection with a stationary post-flare coronal arch. The mass ejection was seen, both by S olwind and Helios, in prolongation of the path of a powerful spray, whereas the active region filament did not erupt. A tentative comparison is made with other occurrences of stationary, or quasi-stationary post-flare coronal arches.

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