Solar Radio Emissions at 4-metres Wave-length During 1947-50 Inclusive and Their Relation to Solar Activity*

Abstract

Bursts at 4·1 metres wave-length of solar radio etrusswn of duration exceeding ¼ minute and intensity greater than |$2\times{10}^{-21}\,\text{watt}\,\text{m}^{-2}\,\text{(c/s)}^{-1}$| are analysed with respect to solar flares in order to determine (1) time differences between flares and radio bursts and (2) the distribution on the solar disk of flares with associated radio bursts. There is a tendency for the onsets of the bursts to lag behind the onsets of the flares; the records of radio intensity, with rapid and spasmodic fluctuations in amplitude, make it difficult to determine onset precisely, but the median lag of bursts behind the flares is about a minute or two. The median lag of the maxima of the bursts behind the flares is also about a minute. It is pointed out, however, that both for onsets and maxima the dispersion of the distribution of time differences between flares and bursts is such that a very appreciable proportion of the radio bursts precede the flares. The analysis of time differences is extended to ionospheric phenomena associated with flares. The distributions all show considerable dispersion, and it appears that there are secondary controlling factors both in the solar phenomena and in the ionosphere with varying influence on any individual occurrence. The analysis of the occurrence of radio bursts with respect to solar longitude from central meridian helps to confirm the previous tentative conclusion that there is a greater chance of radio bursts in association with flares on the eastem half of the visible solar disk than for flares on the westem half. The asymmetry occurs in the observations for each year and the statistical significance becomes increasingly evident.