This paper reviews the relation of solar radio bursts of spectral type IV to the ejection of relativistic and sub-relativistic solar particles; the relation of bursts of types II and IV to the ejection of solar plasma; and radar evidence for quiet solar streaming. Ejection of relativistic and sub-relativistic particles by flares is virtually always accompanied by type-IV radio bursts. The minimum Sun-Earth travel time for these particles is about 20 min. Ejection of plasma from flares accompanied by bursts of types II and IV is considered in terms of subsequent geomagnetic effects. Type IV bursts are highly associated with geomagnetic storms and type II bursts have a small but significant association. The Sun-Earth travel time for the storm plasma is generally 36–48 hr. Type II Bursts may possibly be identified with passage through the corona of a large amplitude shock wave, which then propagates outwards through the interplanetary plasma, causing a geomagnetic sudden commencement when it reaches the earth. The presence of type IV radiation may be indicative of the amount of material transported behind the shock front. Radar observations of the solar corona indicate that at a height of approximately 350,000 km above the photosphere there is a net outward flow of matter at a velocity of about 16 km/sec. This velocity is consistent with Parker's hydrodynamic theory, for coronal temperatures of the order of 106 °K.

This paper describes the characteristics of the radio burst generated by the Class 3 solar flare of 1961 September 28, 2202 U.T. The relation of the radio burst to accompanying X-ray and high-energy proton emission is then briefly examined in terms of existing theories of electromagnetic emission and particle acceleration in the solar atmosphere.

This paper discusses the occurrence and intensity of solar radio bursts at four frequencies in the band 100 to 600 Mc/s. The observations cover 4010 hours during a 12-month period at sunspot maximum; the results refer essentially to bursts of intensity great than 10−1 mks unit and duration greater than 0.3 second; and the statistical information has been interpreted in terms of the spectral characteristics of the bursts. The experimental data were taken at Fort Davis, Texas, and the analysis shows that at 125 Mc/s burst radiation was recorded for 560 hours, of which 380 hours were of low intensity. At 200 Mc/s the burst radiation covered 350 hours, of which 240 hours were of low intensity. For these two frequencies the bursts occurred mainly in the form of noise storms (spectral type I). At 425 and 550 Mc/s the total times of the solar bursts were much less, being respectively 21 and 23 hours; for the most part, however, this radiation was of high intensity and appeared in the form of continuum radiation (spectral type IV) over a wide frequency range.

Current theories of the origin of solar radio bursts suggest that fast drift (Type III) bursts may be generated by the emission of solar particles with velocities approaching those of cosmic rays. An examination of cosmic ray intensity and solar radio data over the two-year period 1956 October–1958 September shows, however, no correlation between fast drift bursts and cosmic ray increases on the earth. Solar flares, with which fast drift bursts are associated, also appear to be unrelated to cosmic ray increases. On the other hand there have been a number of cases of increases in low energy cosmic ray particles, recorded by equipment in satellites and balloons, which were probably related to outbursts of solar continuum (Type IV) radiation. Forbush type decreases in cosmic ray intensity, and accompanying magnetic storms, are regularly preceded by slow drift (Type II) radio bursts.

Slow drift (Type II) radio bursts from the sun are believed to be caused by a primary disturbance moving outward through the solar atmosphere with a velocity of about 1000 km/sec. Analysis of the 2 years, 1956 October 1 through 1958 September 30, over the sunspot maximum shows that 45 per cent of these bursts are associated with the subsequent occurrence of terrestrial auroræ and magnetic storms. The mean delay between the radio bursts and the terrestrial disturbances is 33 hr, which is in good accord with the velocity for the disturbing source as deduced from the radio data. Investigation of the properties of the individual slow drift bursts and their association with other solar radio and optical phenomena reveals no completely conclusive criteria to explain why only 45 per cent of the bursts are geomagnetically important. The geomagnetic effects are enhanced, however, if the bursts occur near the equinoxes and if they are accompanied by a flare o'f importance 2 or 3, or by continuum (Type IV) radiation.